An optimum design of a a-Si//poly-Si tandem solar cell

摘要

A systematic investigation of a high efficiency a-Si//poly-Sifour-terminal structure tandem solar cell has been made using boththeoretical and experimental approaches. It has been shown from optimumdesign theory, used on a realistically attainable best efficiency, thatthe best combination of a tandem solar cell is a-Si/poly-Si siliconmaterials with respect to high achievable efficiency. In the opticaldesign rule, priority of the photon utilization is put on the poly-Sibottom cell. Employing high conductivity with wide optical band gap ptype μc-SiC as a window material and n type μc-Si as back ohmiccontact with BSF treatment, a conversion efficiency of 17.2% has beenobtained for the poly-Si cell. An optimum design of the a-Si top cellhas been experimentally made on a p μc-SiC/p a-SiC/i a-Siμc-Si/ITO structure, and an efficiency of 7.25% has been obtainedwith a 100 nm thick i-layer top cell. The best efficiency of a p-i-nsingle-junction solar cell with this structure is 12.3% so far with a500 nm i-layer thickness device using an Ag back electrode. With a 100nm thick ultra thin top cell, a total conversion efficiency of ana-Si//poly-Si four-terminal tandem solar cell as high as 21.0% has beenachieved