WO2002041363A9

WO2002041363A9 - System and methods for laser assisted deposition

Info

Publication number: WO2002041363A9
Application number: PCT/US2001/043586
Authority: WO
Inventors: Norman F Dessel
Original assignee: Solarflex Technologies Inc; Norman F Dessel
Priority date: 2000-11-16
Filing date: 2001-11-16
Publication date: 2003-11-20
Also published as: AU2002233930A1; WO2002041363A2; WO2002041363A3

Abstract

Systems and methods for laser assisted deposition use an energy source such as a laser to simultaneously deposit and anneal a thin film of semiconductor or metal material on a substrate. The uniform heating of the deposited material while the layer is being sputtered obviates a subsequent annealing stage. The laser can be pulsed or continuous wave. The substrate can be plastic such as tedlar, mylar, teflon, or tefzel. The systems and methods for laser assisted deposition can be used to manufacture solar cells, such as a cadmium telluride (CdTe) solar cell having a cadmium sulfide (CdS) window layer. Both the techniques of sputtering and sublimation can be used to grow the layer.

Description

SYSTEMS AND METHODS FOR LASER ASSISTED DEPOSITION

Related Applications

[01] This application claims the benefit of United States Provisional Application Serial No. 60/249,367, filed November 16, 2000, and United States Provisional Application Serial No. 60/254,760, filed December 12, 2000, and this application is a continuation-in-part of United States Patent Application Serial No. 09/892,131 filed June 25, 2001.

Field of the Invention [02] The present invention relates generally to the deposition of thin films and, more particularly relates to methods and systems for laser assisted deposition.

Background of the Invention

[03] The fabrication of solar cells presents unique manufacturability challenges to the solar energy industry. Chief among them is the difficulty often encountered in depositing the semiconductor layers that form a cell's pn-junction onto a substrate material capable of withstanding high processing temperatures. In the past, this challenge has prevented the manufacture of solar cells on flexible materials such as plastic because many plastics break down or become damaged during high temperature deposition and annealing.

[04] Known deposition systems for creating thin films include evaporation, chemical vapor deposition and sublimation. Deposition is a physical vapor deposition process in which a target material is bombarded by high-energy ions, causing the target material to eject atoms or molecules that are then deposited in a thin layer on the substrate. Deposition is relied on heavily in the solar cell industry for at least two reasons: First, deposition permits the deposition of complex alloys, such as CdTe, CdS, and other compound semiconductors. Second, deposition is ideal for depositing controlled, uniform films onto substrates having large surface area, such as the substrates used to produce solar cells and panels. Sublimation is an alternative technique for depositing a solid state material onto a surface that is also widely used to manufacture solar cells. [05] In semiconductor wafer manufacturing, annealing has traditionally been performed as a follow-on step subsequent to ion implantation or other process step known to damage the crystal lattice. In contrast, thin film manufacturing uses annealing primarily to improve crystalinity of the amorphous deposited layer. In both cases, annealing usually takes place at a temperature of about 500°C. Most plastics break down when exposed to such high heat. As a result, thin film solar cell construction has required a heat tolerant substrate material such as glass. Unfortunately, glass solar cells have limited applications due to their cost and bulkiness. Thus, a manufacturing process and apparatus capable of depositing thin film layers onto a flexible and low-cost plastic or polymeric substrate is desirable.

Summary of the Invention [06] The present invention addresses the drawbacks of prior art thin film deposition techniques noted above and provides systems and methods for laser assisted deposition of thin films.

[07] The systems and methods for laser assisted deposition use a thin film deposition technique that combines thin film deposition and annealing into one processing stage. In one embodiment, the target material for deposition is mounted to a negatively charged cathode in a magnetron or similar processing apparatus having a plasma within a chamber and sputter-depositing the target material onto a substrate to build a thin film layer thereon. In one embodiment the substrate material is a plastic or polymeric material such as tedlar, mylar, tefzel, or teflon. [08] The processing apparatus can be modified to contain an energy source. In one implementation of the invention, the energy source is a laser. The energy source could be any homogenized beam energy source producing electromagnetic energy of any wavelength sufficient to anneal the thin film layer without overheating or damaging the substrate. The energy source can be a pulsed source of very short duration so as to prevent the beam from damaging the substrate. Alternatively, the energy source can be a continuous wave source that is scanned back and forth across the film surface in order to evenly heat the target material as it gets deposited onto the substrate. In both cases, the majority of the energy from the source is ideally absorbed by the film before being passed on to the substrate.

[09] In one embodiment of the invention, the systems and methods for laser assisted deposition are used to manufacture a solar cell, for example a cadmium telluride solar cell having cadmium telluride (CdTe) as the absorption layer and cadmium sulfide (CdS) as^ e^indow layer. Other layers utilizing laser assisted deposition, such as current collection layers, may be necessary to complete the solar cell. [10] The systems and methods for laser assisted deposition may incorporate a radio frequency system, a magnetron, or any other similar apparatus designed for depositing thin films.

Brief Description of the Drawings

[11] The details of the present invention, both as to its structure and operation, may be gleaned in part by study of the accompanying drawings, in which like reference numerals refer to like parts, and in which:

[12] Figure 1 is a diagram of a typical system using a parallel plate DC magnetron used to sputter-deposit thin films.

[13] Figure 2 is an enlarged view of a process chamber used in a typical parallel plate DC magnetron showing the details of particle interaction. [14] Figure 3 is a flow diagram of the basic steps involved in thin film deposition.

[15] Figure 4 is a diagram of a parallel plate DC magnetron as modified to include an energy source according to one embodiment of the systems and methods for laser assisted deposition.

[16] Figure 5 is a flow diagram of one embodiment of the systems and methods for laser assisted deposition which employs sputtering.

[17] Figure 6 is a diagram of a sublimation chamber modified to include an energy source according to one embodiment of the systems and methods for laser assisted deposition. Detailed Description of the Invention

[18] The systems and methods for laser assisted deposition overcome the aforementioned manufacturability problem by providing an energy source with a deposition apparatus that simultaneously deposits and anneals a target material onto a substrate. In one embodiment, the deposition systems and methods employ a simple parallel plate DC diode deposition apparatus. In other embodiments, the deposition apparatus may be a magnetron, an RF system, a sublimation chamber, or any other apparatus designed for manufacturing thin films. [19] Figure 1 is a diagram of a typical system using a parallel plate DC magnetron 100 used to sputter-deposit thin films. Cathode 105 is equipped with magnets 140 and is held at a negative potential with respect to anode 110 by DC power supply 112. Target material 135 is mounted to cathode 105 and substrate material 170 lays atop anode 110. Pressure controller 145 is attached to sputter chamber 180 via pressure control line 190. Gas inlet 115 is connected to gas supply 120 via gas supply line 125. Gas flow controller 130 also connects to gas supply line 125. Pressure controller 145 is also coupled to roughing pump 150 and turbo pump 155 via vacuum control lines 160. Finally, a network of vacuum outtake tubes 165 connects turbo pump 155 and roughing pump 150 to process chamber 180. [20] Figure 2 is an expanded view of process chamber 180 showing the details of particle interaction within magnetron system 100. Positively charged gas ions 205 interact with target material 135 in plasma 215. Dislodged particles 210 from target material 135 migrate toward substrate 170 through plasma 215. Target material 135 can be, for instance, a semiconductor material such as cadmium sulfide, or a metal such as copper, both used in the manufacture of solar cells. Excess matter 220 is removed from process chamber 180 through vacuum outtake 165.

[21] Cathode 105 of parallel plate DC magnetron 100 houses magnets 140 configured around and behind target material 135 to capture and restrict electrons 225 near target material 135. The purpose of magnets 140 is to cause electrons 225 from cathode 105 to spin in the magnetic field created by cathode 180 and anode 110. A single electron 225 can liberate as many as thirty new electrons 225 by impacting and ionizing inert gas atoms 205. Thus, in the dark space near the face of target material 135, spinning electrons 225 ionize the flood of inert gas atoms 205. Ionized inert gas atoms 205, now positively charged, accelerate to collide with the surface of target .material 135. The result is a higher overall deposition rate of magnetron 100 due to a greater number of positively charged ions 205 bombarding target material 135. [22] Other embodiments of process chamber 180 include a simple parallel plate DC diode deposition apparatus having no magnets 140. As just described, magnets 140 are preferable to the extent that they improve the deposition rate. Process chamber 180, so modified to include magnets 140, is commonly called a magnetron. However, process chamber 180 may be further modified such that the electric field between cathode 105 and anode 110 is an RF (radio frequency) field. In this RF embodiment, the deposition apparatus uses RF energy to create the plasma instead of the DC field described above. [23] The basic steps to deposition are depicted in Figure 3. In step 305, positively charged ions of inert gas 205 are generated in plasma 215 in high vacuum chamber 180 and accelerated toward target material 135 at a negative potential. Argon is often the inert gas of choice due to its relative abundance in earth's atmosphere. In step 310, positively charged ions 205 gain momentum and accelerate toward target material 135. Upon physical impact with target material 135 in step 315, particles from target material 135 are physically dislodged. In step 320, the dislodged particles migrate toward the surface of substrate 170. In step 325, the sputtered particles condense and form a thin film on substrate 170 with essentially the same material composition as target material 135. In step 330, excess material 320 is removed from the chamber by vacuum outtake 165. Finally, a typical thin film device manufacturing method also usually comprises a subsequent annealing phase 335 wherein the deposited layer is annealed at high temperature in order to eliminate film irregularity or repair any damage caused to the layer during deposition.

[24] The systems and methods thus far described are suitable for thin film deposition in semiconductor device fabrication situations of all types, including building metallization layers in silicon wafer processing and deposition of the thin film layers comprising a solar cell. In the manufacture of thin film solar cells in particular, annealing step 335 can serve the special purpose of crystallizing an amorphous deposited layer. Deposited layers are often amorphous; hence, the subsequent annealing of such a layer acts to improve the electrical and physical properties of the film by decreasing the number of defects and grain boundaries as the layer progresses toward polycrystal.

[25] Annealing is a thermal treatment usually accomplished in furnaces following layer deposition, or multi-layer deposition. Annealing furnaces typically expose devices to high heat for very long duration. Where the device is a thin film solar cell built on a plastic substrate, both high heat and long duration can cause permanent damage to the substrate. Rapid thermal annealing is an example of a technique that has been developed by process engineers to minimize the exposure of a device to extreme annealing temperatures. However, the high target temperatures reached in a rapid anneal can cause damage to plastic even though the exposure is limited in time. [26] The systems and methods for laser assisted deposition permit the deposition of thin films on plastic substrates by merging the deposition and annealing together in one step. Combined deposition and annealing eliminates the subsequent anneal stage 335 of the thin film process of figure 3. Process chamber 180 is able to simultaneously deposit and anneal the thin film because the system for laser assisted deposition includes an energy source for uniformly heating the target material while it is deposited as further illustrated below. [27] Figure 4 is a diagram of the process chamber of figure 2 as modified to include energy source 410 according to one implementation of the systems and methods for laser assisted deposition. In one embodiment, energy source 410 is designed to emit energy through a port 420 provided in cathode 105 and aimed at substrate 170. However, energy source 410 could be provided at any suitable position within process chamber 180. Also, the vacuum conditions created in process chamber 180 are designed to have negligible effect on the output of energy source 410.

[28] Energy source 410 may be, for instance, any of a number of tunable lasers or masers. Also, the particular type of source selected may be modulated in both beam energy density and beam center frequency. The energy density used is varied in time in synchronization with the particular layer thickness. The high level of control of the energy density is best achieved with a cw (continuous wave) laser with long temporal coherence length. It is often necessary to deposit only a very small total energy per square centimeter of deposition layer. Additionally, the cw beam intensity also may be slowly modulated as cell layer depth increases, using only an amount of intensity that will result in the desired temperature in the selected layer. Control over beam intensity prevents destroying the layer, which could occur if the temperature were to rise too quickly.

[29] Energy source 410 may also be a pulse laser. However, pulse lasers are much more difficult to control in energy delivery to substrate 170 since their energy is delivered in a pulse that has poor temporal coherence by comparison with cw beams. The peaked pulse of the pulse laser output makes it far less desirable as a controlled power source.

[30] In one implementation, energy source 410 is a modified solid state laser such as a Yttrium-Aluminum-Garnet (YAG) laser. In other implementations, energy source 410 is a continuous wave laser. However, the system and method for laser assisted deposition contemplates any of the many types of lasers available including those lasers categorized by the physical state of the active medium employed (i.e., gas, liquid, and solid-state), as well as those lasers categorized by their wavelength (i.e., infrared, visible, and ultraviolet). Energy source 410 is chiefly responsible for ensuring that the deposited layer is adequately annealed at the same time as it gets deposited. In effect, annealing takes place in a layer-by-layer fashion while the thin film is sputtered onto substrate 170.

[31] If energy source 410 is a continuous wave laser light source, the beam emanating from source 410 could be rapidly and continuously scanned back and forth across the film. A stationary continuous beam may cause damage to substrate 170 or to the deposited film if allowed to irradiate an isolated portion of substrate 170 or deposited layer for too long. In whatever implementation of source 410, either continuous wave or pulsed, the energy directed at the thin film surface must be substantially absorbed by the thin film layer itself with as little energy as possible passing to substrate 170. Both the fine tuning of the laser's output and/or a cooling circuit can help to achieve optimal energy absorption and protect substrate 170 in case of excessive exposure. A cooling circuit would contact the reverse side of substrate 170 and provide a temperature differential that can be controlled to keep substrate 170 within the acceptable temperature range.

[32] In one embodiment, port 420 is a clear opening (not shown) in cathode 105 through which a laser beam is able to pass. A window covering port 420 and interfacing with chamber 180 could be used but would have to be frequently cleaned in order to prevent build-up of target material 135 and other matter from obscuring the passage of the beam. In another embodiment, the window is covered with a transparent conductive layer such as indium-tin-oxide (ITO) and charged to a negative potential for repelling particles from target material 135. This repulsion would help control or eliminate the potential build-up of matter on the window and would ease the burden of having to clean the window as frequently.

[33] The systems and methods of laser assisted deposition are easily understood from the process flow diagram of figure 5. In step 505, positively charged ions of inert gas 205 are generated in plasma 215 in high vacuum chamber 180 and accelerated toward target material 135 held at a negative potential. As before, argon gas is frequently chosen for inert gas 205 because it is abundant and inexpensive. In step 510, positively charged ions 205 gain momentum and accelerate toward target material 135. Upon physical impact with target material 135 in step 515, atoms from target material 135 are physically dislodged and upon arriving at the growing thin film layer, are uniformly heated by energy source 410.

[34] Step 520 represents a significant departure from the conventional systems and methods of deposition. Whereas deposition and annealing were two distinct steps in the method and systems of figures 1-3, the systems and methods of laser assisted deposition combine deposition and annealing into one step to produce a thin film layer that is simultaneously annealed while being deposited onto the substrate. The controlled heating of the deposited material in this step anneals the sputtered material at the same time it is being deposited onto substrate 170. Control of the temperature at this stage is critical. The laser light source must generate energy just adequate to ensure that the target material is annealed but without causing harm to the substrate. [35] In step 525, the sputtered atoms condense and form a thin film on substrate 170 with essentially the same material composition as target material 135. Finally, in step 530, excess material 220 is removed from chamber 180 by vacuum pump 165. [36] In addition to controlling the output of energy source 410, the temperature at which laser assisted deposition is carried out must be kept sufficiently low to avoid damaging the plastic or polymer substrate 170. In one embodiment, the systems and methods for laser assisted deposition are carried out at room temperature. In another embodiment, the systems and methods for laser assisted deposition are carried out at or below the temperature above which the thin film of material crystallizes, so long as this temperature does not melt or damage substrate 170. In another embodiment, the systems and methods for laser assisted deposition are carried out below the critical temperature of substrate 170. The critical temperature of substrate 170 is the temperature at which substrate 170 begins to sustain permanent damage. [37] The systems and methods for laser assisted deposition also allow each layer of a cell to be annealed separately as it is produced, rather than annealing an entire stack of layers simultaneously. This advantage means that less energy is used to anneal a single layer; hence, the substrate temperature rise as well as the temperature rise of the underlying layers is minimized. Individual layer annealing also reduces problems that arise due to differences in thermal expansion coefficients of the various layers because the temperature rise of the underlying layers is kept to a minimum. In another embodiment, simultaneous deposition and anneal permits annealing of a portion of the thickness of a layer at a time, further reducing the amount of heat to which the substrate is exposed. [38] A principle purpose of the systems and methods for laser assisted deposition is to optimize the sheet resistance of the deposited layer. Since sheet resistance causes electrical losses in the cell, deposited thin films should have a sheet resistance as low as possible. One way to reduce sheet resistance involves increasing the thickness of the film. The disadvantage to thicker films, at least in the context of solar cells, is reduced flexibility; and in some instances, a thicker cell may undesirably alter the cell's optical absorption properties. Laser assisted deposition is a superior method of improving sheet resistance, which uses a laser beam to control annealing energy without causing the substrate to overheat. All else being equal, the simultaneous annealing disclosed as part of the systems and methods for laser assisted deposition generates films of very low sheet resistance without increasing the thickness of the film. The result is a film of superior crystalline structure having, in addition to a low sheet resistance, a finer structure and larger grain size without high temperature processing.

[39] The systems and methods for laser assisted deposition can be used to create thin film solar cells on a flexible or plastic substrate such as disclosed in pending U.S. Patent Application Serial No. 09/892,131 and said Application is fully incorporated by reference herein as though included in its entirety. Sputter depositing a thin film of the compound semiconductor CdTe has proven difficult; therefore, the systems and methods for laser assisted deposition contemplate the use of sublimation techniques to grow a CdTe absorption layer. Sublimation can be used, however, to grow any layers of a cell, including metallization layers, as an alternative or companion process to sputtering. [40] Figure 6 is a diagram of a typical sublimation chamber 600 modified to include an energy source according to one embodiment of the system and method for laser assisted deposition. Sublimation chamber 600 comprises crucible 610, sublimation material 620, energy source 630, and vacuum outtake 660. Sublimation material 620 can be, for instance, solid state CdTe for use in depositing a CdTe thin film onto substrate 170, according to one embodiment. Sublimation can also be carried out using pure cadmium and pure telluride rather than depositing compound CdTe. Sublimation in this manner could require two crucibles 610 to separately store the cadmium and the telluride. [41] Sublimation includes converting a substance directly from a solid to a gas. Solid material 620 is thus converted to a gas 670 in chamber 600 wherein appropriate vacuum pumps are attached to chamber 600.

[42] Energy source 630 simultaneously anneals gas particles 670 concurrent with their deposition onto substrate 170. As before, energy source 610 can be a maser or laser or any other source regardless of categorization by active medium or wavelength. Continuous wave, rasterized, or pulsed energy is likewise acceptable. [43] Temperature control can be accomplished using a cooling circuit that would maintain a temperature differential at substrate 170 in order to prevent damage to substrate 170. Cooling is also critical during sublimation to ensure that the deposited layer of gas particles 670 are annealed without causing harm to substrate 170. [44] One or more metallization layers using the systems and methods for laser assisted deposition may also be necessary to provide current collection for the cells. Metallization layers as well as semiconductor layers may be deposited using sublimation. Proof-of-principle lab results have yielded solar cells built on high temperature flexible substrates such as mylar, tedlar, teflon, and tefzel using the techniques described herein. By flexible is meant a sheet of finished cells that can be rolled to a minimum inside radius of about four inches such that when unrolled, the cells will not suffer degradation or damage. Also, the selection of a very heat tolerant substrate will produce a cell with higher efficiency because it is possible to raise annealing temperature to higher levels. [45] The description and drawings contained herein represent the presently preferred embodiment of the invention and are, as such, a representative of the subject matter which is broadly contemplated by the present invention. The scope of the present invention fully encompasses other embodiments that may become obvious to those skilled in the art, and the scope of the present invention is accordingly limited by nothing other than the appended claims.

Claims

WHAT IS CLAIMED IS

1. A system for depositing a thin film comprising: a chamber having a cathode and an anode for generating an electric field therebetween; a gas intake for injecting an inert gas into the chamber; a target material affixed to the cathode and exposed to the inert gas whereby positively charged inert gas particles dislodge particles from the target material; an energy source for generating energy inside the chamber; and a substrate affixed to the anode on which substrate the dislodged particles from the target material are deposited to form the thin film and on which the energy from the energy source simultaneously anneals the thin film without damaging the substrate.

2. The system of claim 1, wherein the cathode contains magnets.

3. The system of claim 1, wherein the electric field is an RF (radio frequency) field.

4. The system of claim 1, wherein the electric field is a DC (direct current) field.

5. The system of claim 1, wherein the energy source is a laser.

6. The system of claim 5, wherein the laser is a pulsed laser.

7. The system of claim 6, wherein the pulsed laser is activated for a duration short enough to avoid damaging the substrate.

8. The system of claim 5, wherein the laser is a continuous wave laser.

9. The system of claim 8, wherein the continuous wave laser is scanned back and forth over an upper surface of the thin film to avoid damaging the substrate.

10. The system of claim 1, wherein the inert gas is argon (Ar).

11. The system of claim 1 , further comprising a pump for creating and maintaining vacuum conditions in the chamber.

12. The system of claim 1, further comprising a vacuum outtake for removing excess matter from the chamber.

13. The system of claim 1, further comprising a cooling circuit for controlling the temperature of the substrate.

14. The system of claim 1, wherein the substrate is plastic.

15. The system of claim 14, wherein the plastic substrate is one of the group consisting of tedlar, tefzel, mylar, and teflon.

16. The system of claim 1 , wherein the target material is a semiconductor.

17. The system of claim 16, wherein the semiconductor target material is one of the group consisting of cadmium telluride (CdTe) and cadmium sulfide (CdS).

18. The system of claim 1 , wherein the target material is a metal.

19. The system of claim 18, wherein the metal target material is one of the group consisting of indium-tin-oxide (ITO), copper (Cu), and silver (Ag).

20. A system for depositing a thin film comprising: a chamber; a crucible housed within the chamber for storing a sublimation material; an energy source for generating energy inside the chamber; and a substrate mounted in the chamber, on which substrate gas particles from the sublimation material are deposited to form the thin film and on which the energy from the energy source simultaneously anneals the thin film without damaging the substrate.

21. The system of claim 20, wherein the energy source is a laser.

22. The system of claim 21 , wherein the laser is a pulsed laser.

23. The system of claim 22, wherein the pulsed laser is activated for a duration short enough to avoid damaging the substrate.

24. The system of claim 21 , wherein the laser is a continuous wave laser.

25. The system of claim 20, further comprising a pump for creating and maintaining vacuum conditions in the chamber.

26. The system of claim 20, further comprising a vacuum outtake for removing excess matter from the chamber.

27. The system of claim 20, further comprising a cooling circuit for controlling the temperature of the substrate.

28. The system of claim 20, wherein the substrate is plastic.

29. The system of claim 20, wherein the sublimation material is a semiconductor.

30. The system of claim 29, wherein the semiconductor material is cadmium telluride (CdTe).

31. A method of depositing a thin film comprising: sputtering a thin film of material onto a substrate; and simultaneously directing energy from an energy source at the thin film for annealing of the thin film.

32. The method of claim 31 , wherein the substrate is a polymer or plastic.

33. The method of claim 31 , wherein the energy source is a laser.

34. The method of claim 33, wherein the laser is a pulsed laser.

35. The method of claim 33, wherein the laser is a continuous wave laser.

36. The method of claim 31 , wherein energy from the energy source is directed at the thin film and is at a temperature below the critical temperature of the substrate to avoid damaging the substrate.

37. The method of claim 31 , wherein the thin film of material is a semiconductor.

38. The method of claim 37, wherein the semiconductor is one of the group consisting of cadmium telluride (CdTe) and cadmium sulfide (CdS).

39. The method of claim 31 , wherein the thin film of material is a metal.

40. The method of claim 39, wherein the metallization layer is one of the group consisting of Indium-Tin-Oxide (ITO), Copper (Cu), and Silver (Ag).

41. The method of claim 31 , wherein the steps of sputtering the thin film and directing an energy source both occur in a process chamber having a cathode and an anode for creating an electric field therebetween.

42. The method of claim 41, wherein the electric field is an RF (radio frequency) field.

43. The method of claim 41 , wherein the electric field is a DC (direct current) field.

44. A method of depositing a thin film comprising: sublimating a thin film of material onto a substrate; and simultaneously directing energy from an energy source at the thin film for annealing of the thin film.

45. The method of claim 44, wherein the substrate is a polymer or plastic.

46. The method of claim 44, wherein the energy source is a laser.

47. The method of claim 46, wherein the laser is a pulsed laser.

48. The method of claim 46, wherein the laser is a continuous wave laser.

49. The method of claim 44, wherein energy from the energy source is directed at the thin film and is at a temperature below the critical temperature of the substrate to avoid damaging the substrate.

50. The method of claim 44, wherein the thin film of material is a semiconductor.

51. The method of claim 50, wherein the semiconductor is cadmium telluride (CdTe).

52. The method of claim 44, wherein the thin film of material is a metal.

53. The method of claim 52, wherein the metal is one of the group consisting of Indium-Tin-Oxide (ITO), Copper (Cu), and Silver (Ag).

54. A method of manufacturing solar cells comprising the steps of: depositing a semiconductor layer onto a substrate; simultaneously annealing the semiconductor layer as the layer is deposited on the substrate by directing energy from an energy source onto the semiconductor layer; and depositing a current-collecting metallization layer onto the semiconductor layer or substrate.

55. The method of claim 54, wherein simultaneously annealing comprises directing the energy from the energy source onto the semiconductor layer for a duration long enough to noticeably increase the grain size of the semiconductor layer.

56. The method of claim 54, wherein the energy source is a laser.

57. The method of claim 54, wherein the substrate is plastic.

58. The method of claim 57, wherein the plastic substrate is one of the group consisting of mylar, tedlar, teflon, and tefzel.

59. A solar cell comprising: a flexible substrate; an n-type window layer deposited at a temperature sufficiently low so as not to damage the substrate; and a p-type absorption layer deposited using sublimation at a temperature sufficiently low so as not to damage the substrate.

60. The solar cell of claim 59, wherein the p-type absorption layer comprises cadmium telluride deposited at a temperature sufficiently low to avoid crystallization of the cadmium telluride.

61. The solar cell of claim 59, wherein the n-type window layer comprises cadmium sulfide sputter deposited at a temperature sufficiently low to avoid crystallization of the cadmium sulfide.

62. A thin film flexible solar cell comprising: a plastic or polymer substrate; a thin film of n-type cadmium sulfide deposited at a temperature sufficiently low so as not to damage the substrate; and a comparatively thicker film of p-type cadmium telluride deposited using sublimation at a temperature sufficiently low so as not to damage the substrate.

63. A thin film flexible solar cell comprising: a flexible substrate; a current collection layer deposited onto the substrate; an n-type semiconductor film that is deposited onto the current collection layer and has an amorphous atomic structure; a p-type semiconductor film having a bandgap energy less than the n-type semiconductor film that is deposited using sublimation onto the n-type semiconductor film and has an amorphous atomic structure; and a metallization layer deposited onto the p-type semiconductor film.

64. The thin film flexible solar cell of claim 61 wherein: the substrate is a transparent polymer or plastic; the n-type semiconductor film is cadmium sulfide deposited at a temperature sufficiently low to avoid melting or damaging the substrate; and the p-type semiconductor film is cadmium telluride deposited at a temperature sufficiently low to avoid melting or damaging the substrate.

65. A thin film flexible solar cell comprising: a flexible substrate; a metallization layer deposited onto the substrate; a p-type semiconductor film that is deposited using sublimation onto the metallization layer and has an amorphous atomic structure; an n-type semiconductor film having a bandgap energy greater than the p-type semiconductor film that is deposited onto the p-type semiconductor layer and has an amorphous atomic structure; and a current collection layer deposited onto the n-type semiconductor film.

66. The thin film flexible solar cell of claim 65 wherein: the substrate is a transparent polymer or plastic; the p-type semiconductor film is cadmium telluride deposited at a temperature sufficiently low to avoid melting or damaging the substrate; and the n-type semiconductor film is cadmium sulfide sputter deposited at a temperature sufficiently low to avoid melting or damaging the substrate.

67. A method for manufacturing a thin film flexible solar cell comprising the following steps: (a) providing a plastic or polymer substrate;

(b) depositing a layer of an n-type semiconductor on the substrate at a temperature sufficiently low to avoid melting or damaging the substrate; and

(c) sublimating a layer of a p-type semiconductor on the n-type semiconductor layer at a temperature sufficiently low to avoid melting or damaging the substrate.

68. The method of claim 67, wherein: after step (a), a transparent conductive oxide layer is deposited on the substrate and a metal bar bus network is deposited on the transparent conductive oxide layer; and after step (c), a metallization layer is deposited on the p-type semiconductor layer.

69. The method of claim 68, wherein the n-type semiconductor is cadmium sulfide and the p-type semiconductor is cadmium telluride.

70. A method for manufacturing a thin film flexible solar cell comprising the following steps:

(a) providing a plastic or polymer substrate;

(b) sublimating a layer of a p-type semiconductor on the substrate at a temperature sufficiently low to avoid melting or damaging the substrate; and (c) depositing a layer of an n-type semiconductor on the p-type semiconductor at a temperature sufficiently low to avoid melting or damaging the substrate.

71. A method as claimed in claim 70, wherein steps (b) and (c) are carried out at a temperature sufficiently low to avoid crystallization of the semiconductors.

72. A method as claimed in claim 70, wherein the p-type semiconductor is cadmium telluride and the n-type semiconductor is cadmium sulfide.