Vapor‐Transport‐Deposited Orthorhombic‐SnSe Thin Films: A Potential Cost‐Effective Absorber Material for Solar‐Cell Applications
Raju Nandi, Pravin S. Pawar, KrishnaRao Eswar Neerugatti, Jae Yu Cho, Seongheon Kim, Seong Ho Cho, Yun Seog Lee, Jaeyeong Heo
Abstract
The power‐conversion efficiencies of orthorhombic tin selenide (α‐SnSe)‐based thin‐film solar cells (TFSCs) are very low—less than 1% in most cases—due to the poor crystallinity, small grains, and large number of defects. Herein, the highest cell efficiency of 2.51% together with a high short‐circuit current density of 28.07 mA cm −2 for α‐SnSe TFSCs grown via vapor‐transport‐deposition (VTD) is reported. The grain size and surface roughness of the SnSe thin films greatly influence the shunt properties of the device. Significantly large shunt losses are detected in the case of both small and extremely large grains. The shunt losses for SnSe thin film with small grains are associated with high grain‐boundary scattering. The presence of extremely large grains results in high surface roughness of the SnSe thin film, which causes nonuniform deposition of the CdS buffer layer and, consequently, higher shunt losses. The SnSe thin film with moderate‐sized grains and inferior surface roughness exhibits improved shunt properties owing to uniform deposition of the CdS buffer layer and subsequent layers and thereby significant improvement in the device performance. The potential of orthorhombic VTD‐SnSe thin films as an emerging cost‐effective absorber layer for TFSCs is experimentally demonstrated.