Back Contact Interfacial Modification in Highly-Efficient All-Inorganic Planar n-i-p Sb₂Se₃ Solar Cells

Sb₂Se₃ is an emerging and promising light-absorbing material with superior photovoltaic properties. However, the specific one-dimensional structure of Sb₂Se₃ limits the doping density, preventing a high built-in potential. Moreover, in the superstrate devices the back contact is often non-ohmic. In this work, we have successfully applied tungsten oxide (WO_3-) as a hole-transport layer in superstrate n-i-p Sb₂Se₃ solar cells. It is found that an interfacial dipole is formed at Sb₂Se₃/WO_3- interface via Sb-W bonds, which reduces the barrier for hole extraction. Meantime, gap states are present at a suitable energy level to serve as intermediate states for hole-transport from the Sb₂Se₃ absorber to the metal anode. In addition, the introduction of WO_3- can suppress carrier recombination at the back interface, enhance the built-in potential, and improve the spectral response in the long-wavelength region. Consequently, the superstrate devices with the incorporated WO_3- layer achieve a champion efficiency of 7.10% due to the enhancement of all device parameters. Furthermore, the all-inorganic devices with WO_3- hole-transport layer exhibit excellent air stability and thermal stability.