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⁺μc-Si:H window layers on top of 1 Ωcm n-type c-Si. Microcrystalline layers were obtained using moderate PECVD deposition conditions and showed appreciable crystalline volume fraction (~22%), and good window properties. Solar cells made with such window layers have the following structure: Ag/ITO/p⁺ μc-Si:H/buffer/n-c-Si/Al. The presence of a thin (~2 nm) intrinsic a-Si buffer layer deposited at low temperature was found to be essential to achieve high V_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⁺ μc-Si:H layer which explains the higher V_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