Device study and optimisation of CZTS/ZnS based solar cell with CuI hole transport layer for different conduction band offset

Abstract

The copper zinc tin sulphide (CZTS) is a promising candidate for solar cell application. The CZTS/ZnS-based heterojunction provides a high conduction band offset at the junction. The three types of conduction band offset (spike, flat, and cliff) are discussed in the study, and the comparison of cell output variation is also discussed. In this simulation-based study, we have performed optimisation of the device for layer thickness, carrier mobility, defects, front contact transmission profile, and both the series and shunt resistance. A high acceptor type defect density in CZTS increases open-circuit voltage by shifting the Fermi level towards the valance band maximum. The introduction of CuI as a hole transport layer (HTL) offers a low Schottky barrier and delivers high efficiency compared to the same without the CuI layer, while a higher CuI thickness produce a barrier to back reflection. The finally optimised cell gives the highest power conversion efficiency of 15.53% for a spike like conduction band offset of 0.06 eV. This simulation paves a way to fabricate realistic CZTS solar cells based on the present cell model.