Solar Photovoltaic Technologies

Transcription

1 Solar Photovoltaic Technologies Lecture-33 Prof. C.S. Solanki Energy Systems Engineering IIT Bombay

2 Contents Brief summary of the previous lecture Various Thin film solar cell technologies a-si CdTe, CIGS Thin film crystalline Si Choice of material for thin film solar cell 8/1/2008 IIT Bombay, C.S. Solanki Solar Photovoltaic Technologies L33-2

3 Thin-film technologies Amorphous Si a-si:h a-si tandem cells (a-sic, a-sige) (6% market share) II-VI, ternary compound CdTe C(I,Ga)Se 2 (1% market share) Crystalline Si C/nc- Si Poly-Si Multicrystalline-Si Mono-Si Under development 8/1/2008 IIT Bombay, C.S. Solanki Solar Photovoltaic Technologies L33-3

4 IQE Lecture-33 Thin-film technologies Amorphous Si a-si:h a-si tandem cells (a-sic, a-sige) (6% market share) II-VI, ternary compound CdTe C(I,Ga)Se 2 (1% market share) Crystalline Si C/nc- Si Poly-Si Multicrystalline-Si Mono-Si Under development Tandem Material Device structure cells band direct Defects gap band introduces profiling gap the mid gap states short life time double tunable junction, band gap, triple 1.3 junction to 2.0 ev p-i-n/n-i-p structure deposition techniques: thin PECVD,VHF-PECVD, i layers are advantageous HWCVD Light good induced light trapping degradation is required 8/1/2008 IIT Bombay, C.S. Solanki Solar Photovoltaic Technologies L33-4

5 Thin-film technologies Amorphous Si a-si:h a-si tandem cells (a-sic, a-sige) (6% market share) II-VI, ternary compound CdTe C(I,Ga)Se 2 (1% market share) direct band gap 1.45eV(CdTe), 1.1eV(CIGS) heterojunction with n-cds Solar cells are stable and technology is relatively cost effective material availability Toxicity of Cd Crystalline Si C/nc- Si Poly-Si Multicrystalline-Si Mono-Si Under development 8/1/2008 IIT Bombay, C.S. Solanki Solar Photovoltaic Technologies L33-5

6 Thin-film technologies Amorphous Si a-si:h a-si tandem cells (a-sic, a-sige) (6% market share) II-VI, ternary compound CdTe CdS C(I,Ga)Se 2 (1% market share) Crystalline Si C/nc- Si Poly-Si Mono-Si C/Mono-Si (HIT)* Under development non-toxicity abundant raw material experience from microelectronics industry Stability 8/1/2008 IIT Bombay, C.S. Solanki Solar Photovoltaic Technologies L33-6

7 Thin film solar cells: Choice of material andidates for thin-film solar cells: Crystalline Si(c-Si), amorphous Si (a-si), Cadmium teluride (CdTe), Copperindium-gallium-arsenide (CIGS), Gallium-arsenide ( GaAs) GaAs efficiencies above 30%, But very expensive, mainly suited for space application, As is toxic CdTe Cd is toxic, covering large surface area with toxic material is not desirable CIGS Availability of In, 0.08 ppm, cost can go high in case of increased demand a-si low-cost, but low stable efficiency C-Si abundant raw-material ( ppm) high efficiency, stable efficiency, thin-film technology provides potential to reduce the cost of wafer based cells, very attractive option to explore 8/1/2008 IIT Bombay, C.S. Solanki Solar Photovoltaic Technologies L33-7

8 Thin-film technologies: Case for Si Calculated AM1.5 efficiencies (dashed line) and AM0 efficiencies (solid line), comparing achieved cell efficiencies (laboratory-best, confirmed) for various technologies C-Si is near the maximum of this curve Studies shows that if cell are made with thin-film crystalline Si such that they trap enough light, cell efficiencies greater than 20% can be obtained even in just few micron thick layer 8/1/2008 IIT Bombay, C.S. Solanki Solar Photovoltaic Technologies L33-8

9 Techniques for Si usage reduction Reduction of Si-usage Si-ribbons (no kerf loss) EFG-ribbons String ribbons RGS-ribbons Advanced techniques for thin wafers Laser cutting Electrochemical cutting Thickness < 100 m < 80 m 300 m 50 m Thin-film crystalline Si solar cells / High-temperature Thin-film crystalline Si solar cells / Low-temperature m 1 2 m 8/1/2008 IIT Bombay, C.S. Solanki Solar Photovoltaic Technologies L33-9

10 Reduction of Si-usage / pro s con s Reduction of Si-usage Pro s Con s Si-ribbons (no kerf loss) EFG-ribbons (RWE Solar) String ribbons RGS-ribbons Advanced techniques for thin wafers Laser cutting Electrochemical cutting Thin-film crystalline Si solar cells / Hightemperature High quality High quality High throughput: 6000 cm 2 /min High-quality wafers Solar cell process for thin wafers proven in lab (ISE > 19%) High growth rates: 1 5 m/min Throughput: 100 cm 2 /min Throughput: 100 cm 2 /min High defect density: cm -2 No processes available No high-throughput equipment, need for hightemperature substrates 1 2 m Proven: Lab: 13-14% (Kaneka) Production: 9-10% Low growth rates: 1 m/h Sensitivity of p-i-n structure Thin-film crystalline Si solar cells / Lowtemperature 8/1/2008 IIT Bombay, C.S. Solanki Solar Photovoltaic Technologies L33-10

11 Crystalline Si films: challenges & potentials Potentials Cost-effectiveness Material quality and efficiency Challenges Light trapping Surface passivation Grain boundary passivation Supporting substrate SiO 2 C Metallurgical grade Si chlorosilanes CVD V oc V oc. I sc. FF P kt q in J ln( J L o 1) Semiconductor grade Si melting J ob qn N 2 i A D L n p SbL 1 ( S n b / Dn L / D n n tanh( Wb / Ln ) )tanh( W / L n n ) Cz-Si Wafering Block casting Wafering ribbon Thin-film Si Thin-film solar cells smaller volume of recombination tolerance to lower quality material 8/1/2008 IIT Bombay, C.S. Solanki Solar Photovoltaic Technologies L33-11

12 Contents Motivation Different thin-film solar cell technologies Why crystalline Si films? Classification based on grain size Thin-film solar cell structures Deposition techniques low temperature High temperature approaches Mono-crystalline Si thin films Other concepts 8/1/2008 IIT Bombay, C.S. Solanki Solar Photovoltaic Technologies L33-12

13 Classification of different approaches A large number of different technologies are under parallel development A classification can be made based on different criteria: According to T max during layer formation According to grain size According to cell structure The R&D on the high-temperature routes is mainly driven by considerations from classical bulk Si cells Proven high efficiency and stability The R&D on the low-temperature routes is mainly driven by considerations from a-si:h solar cells low thermal budget processing 8/1/2008 IIT Bombay, C.S. Solanki Solar Photovoltaic Technologies L33-13