All‐Vacuum‐Processed Full‐Inorganic Sb ₂ S ₃ Indoor Photovoltaics Based on Magnetron Sputtered TiO ₂ Electron Transport Layers

ABSTRACT The indoor photovoltaic (IPV) technology is an advanced energy harvesting solution to power electronics for the sustainable Internet of Things. Sb 2 S 3 is a highly promising environmentally friendly absorber for IPVs in view of its ideal bandgap of ∼1.75 eV. However, the current high‐performance Sb 2 S 3 solar cells typically involve the use of CdS and Spiro‐OMeTAD charge transport layers, which cause severe toxicity and stability concerns. In this work, we developed all‐vacuum‐processed full‐inorganic Sb 2 S 3 solar cells based on magnetron sputtered TiO 2 electron transport layers. Through comprehensive characterization of structural, morphological, spectroscopic and optoelectronic properties, it is revealed that magnetron sputtered TiO 2 ‐based devices outperform those of solution‐processed counterparts, mainly due to (1) the increase in the oxygen vacancy density of TiO 2 that promotes the subsequent growth of preferential [hkl, l≠0] orientation of close‐spaced sublimation processed Sb 2 S 3 absorber, and (2) the optimization of energy band at the TiO 2 /Sb 2 S 3 heterojunction that reduces charge recombination losses. The as‐obtained Sb 2 S 3 devices deliver a power conversion efficiency of 5.72% under one‐sun illumination, which is the highest reported thus far for all‐vacuum‐processed Sb 2 S 3 solar cells. Furthermore, this device demonstrates a remarkable 14.28% indoor efficiency under 1000 lux WLED. This study provides a feasible all‐vacuum fabrication technology for industrializing Sb 2 S 3 IPVs.