Importance of Fine Control of Se Flux for Improving Performances of Sb₂Se₃ Solar Cells Prepared by Vapor Transport Deposition

Sb₂Se₃ possesses a quasi-1D (Q1D) structure, which creates an anisotropic charge transporting behavior in which the carrier transport is very efficient along the Q1D direction, which is beneficial for solar cells as long as the absorber is properly aligned along the preferred orientation. However, Sb₂Se₃ is prone to form donor-like defects, such as V_Se, that are detrimental to the performance. Therefore, both growth of Sb₂Se₃ along the preferred orientations and the suppression of the formation of V_Se are crucial in achieving Sb₂Se₃ solar cells with a high efficiency. Herein, the importance of fine control of the extra supply of Se during the deposition of Sb₂Se₃ in controlling crystallographic orientations and the population of V_Se in the Sb₂Se₃ films is described. This control determines the performance of the resulting solar cells in a superstrate configuration with a CdS buffer. Incorporation of Se during the growth resulted in a larger open-circuit voltage due to the passivation of V_Se. However, an excess supply of Se disrupts the favorable orientation by selenizing the top region of the CdS, and therefore degraded the short-circuit current. Through the optimization of the extra supply of Se vapor, the power conversion efficiency is improved from 3.7% to 5.2%.