Planar Heterojunction Solar Cell Employing a Single-SourcePrecursor Solution-Processed Sb2S3 Thin Filmas the Light Absorber

摘要

We discuss here a solution-processed thin film of antimony trisulphide (Sb2S3; band gap ≈ 1.7 eV; electronic configuration: ns²np⁰) for applications in planar heterojunction (PHJ) solar cells. An alternative solution processing method involving a single-metal organic precursor, viz., metal–butyldithiocarbamic acid complex, is used to grow the thin films of Sb2S3. Because of excess sulphide in the metal complex, the formation of any oxide is nearly retarded. Sb2S3 additionally displays structural anisotropy with a ribbon-like structure along the [001] direction. These ribbon-like structures, if optimally oriented with respect to the electron transport layer (ETL)/glass substrate, can be beneficial for light-harvesting and charge-transport properties. A PHJ solar cell is fabricated comprising Sb2S3 as the light absorber and CdS as an ETL coated on to FTO. With varying film sintering temperature and thickness, the typical ribbon-like structures predominantly with planes hkl: l = 0 stacked horizontally along with respect to CdS/FTO are obtained. The morphology of the films is observed to be a function of the sintering temperature, with higher sintering temperatures yieldingcompact and smooth films with large-sized grains. Maximum photon toelectricity efficiency of 2.38 is obtained for PHJ solar cells comprising480 nm thick films of Sb2S3 sintered at 350°C having a grain size of few micrometers (>5 μm). Thestudy convincingly shows that improper grain orientation, which maylead to nonoptimal alignments of the intrinsic structure with regardto the ETL/glass substrate, is not the sole parameter for determiningphotovoltaics performance. Other solution-processing parameters canstill be suitably chosen to generate films with optimum morphology,leading to high photon to electricity efficiency.