Deciphering 2D perovskite's role in perovskite solar cells via intact 3D/2D junctions

To advance perovskite solar cells (PSCs) beyond their present efficiency threshold, it is essential to meld device-centric insights with strategies addressing defect passivation issues. Given that 2-dimensional (2D) perovskite, which is commonly utilized to control defects in light-harvesting layers, is used, understanding 3D/2D junctions is crucial for effective device design, as an electric field can be induced at this junction. In this study, we introduce that understanding with the formation of an intact 3D/2D bilayer using (BA)(2)PbBr4 (BA: butylammonium) with deeper work functions, leading to a certified performance of 25.4% compared to (BA)(2)PbI4. While the optoelectronic and defect-related characteristics did not significantly change in accordance with 2D perovskites, an enhancement in built-in potential was observed in the device, which was attributed to the work function of the 2D perovskites. Additionally, through analysis of the p-p isotype heterojunction, it was observed that the built-in potential formed by (BA)(2)PbI4 exists in the 2D layer, whereas the introduction of (BA)(2)PbBr4 shifted the formation of the built-in potential to the 3D layer. The device with a 3D/(BA)(2)PbBr4 heterojunction maintained 89% of its stabilized efficiency after 770 hours in a long-term operational test under 1-sun conditions. The stability of the device, as well as its efficiency, was improved at 85 degrees, offering valuable strategies for the development of high-performance and reliable PSC junctions.