a-Si/poly-Si two- and four-terminal tandem type solar cells

The theoretical and experimental design of a-Si/poly-Si tandem-type solar cells has been performed, and it is shown that the theoretical limit of their conversion efficiency is 25% under AM1.5, 100 mW/cm² solar radiation. A series of experimental trials to find the optimum design parameters has been made on a-Si/poly-Si solar cells of both two- and four-terminal structures. Microcrystalline SiC/poly-Si heterojunctions prepared using electron cyclotron resonance (ECR) plasma chemical vapor deposition (CVD) as well as c-Si p-n junctions formed by the conventional thermal diffusion process have been fabricated, i.e., ITO/n-i-p a-Si n⁺ -p c-Si cells (two-terminal), ITO/p-i-n a-Si/p⁺ -n poly-Si cells (two terminal), and glass/ITO/p-i-n a-Si/ITO/ITO/p⁺-n poly-Si four-terminal cells. The best cell performance achieved was 16.8% on the four-terminal device. Technical data on both cell structures are discussed