Controlled thickness of a chemical-bath-deposited CdS buffer layer for a SnS thin film solar cell with more than 3% efficiency

Abstract

Tin monosulfide (SnS) is considered a promising earth-abundant absorber material for thin film solar cells (TFSCs) with a theoretical power conversion efficiency (PCE) as high as 30%. However, the maximum PCE reported thus far is just 4.36%. This inferior device performance is attributed to low values of open-circuit voltage. In addition to the dense and pinhole-free surface morphology of the phase-pure p-type SnS thin film absorber, a controlled growth of the n-type buffer layer is a prerequisite for enhanced device performance. In this study, we explore the manner in which the thickness of a chemical-bath-deposited n-type CdS buffer layer influences the performance of SnS/CdS TFSCs. The thickness of the buffer layer was adjusted by varying the deposition time from 15 to 25 min, which resulted in thicknesses of 30–80 nm. Initially, the performance parameters of the TFSCs improved with the buffer layer thickness, but later deteriorated with thicker CdS layers. The highest PCE achieved was 3.05% at an optimized CdS buffer layer thickness of approximately 42 nm. This performance was accompanied by a significant decrease in reverse saturation current and shunt conductance, as evidenced by the current density–voltage characteristics under dark conditions.