Insights on the Thermal Stability of the Sb₂Se₃ Quasi-1D Photovoltaic Technology

This work explores the thermal stability of antimony-based photovoltaic (PV) technologies investigating the effect of low-temperature (50-350 degrees C) postdeposition annealings (PDAs) on bare Sb2Se3 absorbers and complete SLG/Mo/Sb2Se3/CdS/i-ZnO/ITO devices (5.7% power conversion efficiency with no anti-reflecting coating or metallic grid). A comprehensive structural analysis by means of X-ray diffraction and Raman spectroscopy, coupled with optoelectronic characterization, reveals clear evidences of a degradation process dominated by selenium diffusion. The degradation process is observed to start at low PDA temperatures as a shrinkage of the Sb2Se3 unit cell. Further increasing the PDA temperature above 200 degrees C leads to the formation of Sb oxides and Se secondary phases in bare absorbers, and of CdS1-xSex in complete devices at the Sb2Se3 front interface which completely degrade the heterojunction and kill device performance. Furthermore, a clear correlation is found between PV performance decrease and Sb2Se3 layer lattice shrinkage with the increasing PDA temperature (T > 50 degrees C). This is the first time that thermal instability is reported for the Sb2Se3 compound at temperatures commonly used during PV module fabrication processes such as emitter/transparent conducting oxide deposition or encapsulation.