Reactive Ion Etching Activating TiO2 Substrate for Planar Heterojunction Sb2S3 Solar Cells with 6.06% Efficiency

Antimony sulfide is a promising photovoltaic material for the top subcell of Si‐based tandem solar cells due to its suitable bandgap, high absorption coefficient, low cost, and environmentally friendly properties. However, the electron transport layer (ETL) of antimony sulfide solar cells is generally based on CdS, while narrow‐bandgap CdS ( E g = 2.4 eV) absorbs part of the short‐wavelength light causing spectral loss. Unfortunately, Sb 2 S 3 films could not be deposited uniformly on TiO 2 substrate by the hydrothermal method. For the first time, reactive ion etching (RIE) treatment to TiO 2 surface is developed to activate it for later Sb 2 S 3 deposition. Based on this strategy, the obtained Sb 2 S 3 film is almost the same as that deposited on CdS, smooth, dense, and uniform. The optimal device efficiency can reach 6.06%, a top value among TiO 2 /Sb 2 S 3 devices with a new record of short‐circuit current density (≈19.4 mA cm −2 ). The high efficiency on RIE‐treated TiO 2 ETL is attributed to the high transparency of TiO 2 and the high‐quality Sb 2 S 3 thin film with suppressed recombination in the Sb 2 S 3 bulk film and TiO 2 /Sb 2 S 3 interface. This work proposes a simple and efficient strategy for deposition of high‐quality Sb 2 S 3 thin films on inert substrates.