Nickle oxide based carrier-selective contact silicon solar cells: Role of forming gas annealing on the device performance
Mrutyunjay Nayak, Sourav Mandal, Ashutosh Pandey, Vamsi Krishna Komarala
Center for Energy Studies, Indian Institute of Technology Delhi, New Delhi, India

Carrier selective contact based silicon heterojunction solar cells are fabricated using Nickle Oxide (NiOx) as a hole selective layer and Lithium Fluoride (LiF) as an electron selective layer. The carrier-selective layers and metal contacts are deposited by thermal evaporation, and the ITO layer by magnetron sputtering system. As-prepared Ag/ITO/NiOx/n-Si/LiF/Al device structure has shown the power conversion efficiency of ~10.23% from 1.2 cm × 1.2 cm device area. Performance of the device is enhanced to ~12% after annealing in the forming gas ambient (FGA: 5% H2 + 95 % N2) at 100 °C for 60 sec. An enhancement in the minority carrier lifetime, open circuit voltage (VOC), and carrier collection efficiency is observed after the FGA annealing. The enhancement is due to an improvement in the NiOx/n-Si interface passivation and reduction in band-offset for minority charge carriers after the better crystallization of NiOx. Whereas; the FGA annealing at 300 °C for 60 sec has led the VOC enhancement from 567 to 600 mV, but, the overall device performance is reduced to ~11.11% due to reduction in the carrier collection efficiency at longer wavelength region (adverse effect from the n-Si/LiF junction). Further optimization of NiOx thin film for reducing tunneling resistance, FGA annealing temperature and time, and effective silicon surface passivation by additional dielectric layers are considered for enhancing the device performance. 

Area: Sub-Area 4.4: Passivated Contacts, Carrier Selective Contacts and Hetero-Junction Structures