Atomic-layer-deposited TiO2 and SnO2 coupled with CdS as double buffer layers for HTL-free Sb2S3 thin-film solar cells

• Atomic layer deposition of SnO 2 and TiO 2 buffer layers . • Structural and morphological study of Sb 2 S 3 deposited on double buffer layers. • Fabrication of superstrate architecture Sb 2 S 3 solar cell devices. • Improvement in efficiency from ∼3.0% to ∼4.23% using double buffer layers. The application of double buffer layers has been proven to be a beneficial approach for the enhancement of the power conversion efficiency (PCE) of antimony sulfide (Sb 2 S 3 ) thin-film solar cells (TFSCs). Recently, solution-processed SnO 2 /CdS, TiO 2 /CdS, ZnMgO/CdS, and ZnSnO/CdS electron transport layers (ETLs) have been investigated as double buffer layers for Sb 2 S 3 TFSCs. Herein, atomic-layer-deposited (ALD) SnO 2 and TiO 2 ETLs were applied as a double buffer layer with CdS for Sb 2 S 3 TFSCs. The Sb 2 S 3 absorber was deposited using a facile hydrothermal method. The TFSC devices were fabricated based on FTO/SnO 2 /CdS/Sb 2 S 3 /Au or FTO/TiO 2 /CdS/Sb 2 S 3 /Au structure without hole transport layers (HTLs). Experimental analysis revealed the reduction of the surface roughness of ETLs and decreased unfavorable (hk0) orientation of the Sb 2 S 3 absorber after utilizing double buffer layers. Initially, incomplete nucleation of Sb 2 S 3 was observed on SnO 2 and TiO 2 ETLs, which resulted in the formation of a shunting path. Conversely, complete nucleation of Sb 2 S 3 was observed on CdS and double buffer layers. The highest PCEs of 3.98% and 4.23% were obtained for SnO 2 /CdS and TiO 2 /CdS double-buffer-layer-based cells with improvements exceeding 1% compared with the reference CdS buffer layer. Additionally, improvements in open-circuit voltage ( V OC ) of the order of ∼25 mV and ∼45 mV were respectively observed for SnO 2 /CdS ( V OC = 0.676 V) and TiO 2 /CdS ( V OC = 0.696 V) double-buffer-layer-based devices compared with the reference CdS buffer layer ( V OC = 0.648 V). The enhanced device properties are mainly attributed to the improved charge carrier collection and formation of suitable band offset at the absorber and ETLs interfaces.