Microcrystalline-crystalline silicon heterojunction solar cells using highly conductive thin p-type microcrystalline silicon window layers

Microcrystalline-crystalline silicon heterojunction solar cells were made using thin (20 nm) p/sup +//spl mu/c-Si:H window layers on top of 1 /spl Omega/cm n-type c-Si. Microcrystalline layers were obtained using moderate PECVD deposition conditions and showed appreciable crystalline volume fraction (/spl sim/22%), and good window properties. Solar cells made with such window layers have the following structure: Ag/ITO/p/sup +/ /spl mu/c-Si:H/buffer/n-c-Si/Al. The presence of a thin (/spl sim/2 nm) intrinsic a-Si buffer layer deposited at low temperature was found to be essential to achieve high V/sub oc/ and efficiencies. From simulation studies, the authors found that the wide band gap buffer layer reduces the recombination losses occurring in the low mobility gap p/sup +/ /spl mu/c-Si:H layer which explains the higher V/sub oc/ values. The highest efficiency (12.2%) was obtained on cells with a 2.5 nm buffer layer deposited after an extra atomic hydrogen pretreatment of the n-type c-Si.