Study on the improvement of the open-circuit voltage of NiOx/Si heterojunction solar cell

Abstract

Heterojunction solar cell based on nickel oxide ( NiO x ) as hole selective layer and n-type silicon as an active absorption layer is a promising high-efficiency solar cell. Unfortunately, this type of solar cells suffers from a low open circuit voltage ( V O C ) which limits any significant progress in its performance. Therefore, the main scope of this study is focused on V O C improvement. Discrete traps at the NiO x /Si interface are taken into account in the simulation to describe the real situation. The simulation was performed by SILVACO-Atlas using the interfacial traps NiO x /Si concentrations and hole mobility as tools to obtain agreement with measurement reported by Hsu et al. in [Thin Solid Films. 573 (2014) 159–163]. These parameters were found to be the cause of the low V O C value. V O C and efficiency improvements were achieved by optimizing the NiO x thickness and insertion a hydrogenated amorphous Si (a-Si:H) thin layer with optimal properties (electron affinity, bandgap and thickness)as a buffer layer between NiO x and Si. V O C increased from 423 to 906.16 mV and a good promising efficiency of η = 12.73 % is obtained in comparison to the initial efficiency (4.50%). • NiO x /Si heterojunction solar cell suffers from a low open circuit voltage. • This study focuses on finding the reason of low open circuit voltage. • A good agreement with the measured values was achieved. • An amorphous hydrogenated silicon buffer layer is inserted and optimized.