Grain Engineering of Sb 2 S 3 Thin Films to Enable Efficient Planar Solar Cells with High Open-Circuit Voltage.

Sb 2 S 3 is a promising environmentally-friendly semiconductor for stable and high efficiency thin film solar cells, but, like many other polycrystalline materials, is limited by non-radiative recombination and carrier scattering by grain boundaries. Herein, we show how the grain boundary density in Sb 2 S 3 films can be significantly reduced from 1068±40 nm µm -2 (largest grain ∼5 µm) to 327±23 nm µm -2 (largest grain >15 µm) by incorporating an appropriate amount of Ce 3+ into the precursor solution for Sb 2 S 3 deposition. Through extensive characterization of the structural, morphological and optoelectronic properties, complemented with computations, we reveal the underlying mechanisms responsible for the increased grain size and improved photovoltaic performance of Sb 2 S 3 solar cells. A critical factor behind the reduction in grain boundary density is the formation of an ultrathin layer of Ce 2 S 3 at the CdS/Sb 2 S 3 interface, which could reduce the interfacial energy and increase the adhesion work between Sb 2 S 3 and the substrate to encourage heterogeneous nucleation of Sb 2 S 3 , as well as increase the rate of grain growth. Through a reduction in non-radiative recombination at grain boundaries and/or the CdS/Sb 2 S 3 heterointerface as well as improved charge-carrier transport properties at the heterojunction, we achieved high performance Sb 2 S 3 solar cells with a power conversion efficiency reaching 7.66%, and an open-circuit voltage (V OC ) of 796 mV. This V OC is the highest reported thus far for Sb 2 S 3 solar cells. This work provides a strategy to simultaneously regulate the nucleation and growth of Sb 2 S 3 absorber films via in-situ chemical environment tuning, which can be more broadly applied to other thin film systems to improve their photovoltaic performance. This article is protected by copyright. All rights reserved.