Space-Charging Interfacial Layer by Illumination for Efficient Sb₂S₃ Bulk-Heterojunction Solar Cells with High Open-Circuit Voltage

Solution-processed material systems for effective photovoltaic conversion are the key to low-cost and efficient solar cells. While antimony trisulfide (Sb 2 S 3 ) is a promising photovoltaic absorber, solution-processed quality Sb 2 S 3 -based heterojunction systems for solar cells, particularly with an open-circuit voltage ( V oc ) higher than 0.70 V, are challenging issues. Here, a cadmium sulfide (CdS) interfacial engineering method is developed for the Sb 2 S 3 -based bulk-heterojunction (BHJ) solar cells with an efficiency of 6.14% and a V oc up to 0.76 V that is the highest one among solution-processed Sb 2 S 3 solar cells. The prepared Sb 2 S 3 -based BHJ solar cells feature a Sb 2 S 3 nanoparticle film interdigitated by a titania (TiO 2 ) nanorod array with a nanostructured CdS shell as an interfacial layer on each TiO 2 nanorod core. Upon understanding the interfacial interactions and band alignments in the TiO 2 –CdS–Sb 2 S 3 system, the function of the CdS interfacial layer as a band-bended spatial spacer interacting strongly with both the TiO 2 electron transporter and Sb 2 S 3 absorber for increasing charge collecting efficiency is revealed; moreover, space-charging the band-bended CdS layer by illumination is found and a photogenerated interfacial dipole electric field model is proposed for understanding the high V oc subjected to the presence of the CdS interfacial layer. This work provides a conceptual guide for designing efficient inorganic heterojunction solar cells.