Sensing of the charge transfer process in ZnO/MAPbI₃ heterojunctions of perovskite solar cells (PSCs) by surface-enhanced Raman scattering

In perovskite solar cells (PSCs), the charge transfer (CT) process at the electron transport layer/photosensitive layer heterojunction has a significant effect on the power conversion efficiency. However, obtaining nondestructive and microscopic information of the interfacial CT process is still challenging. Here, taking advantage of the surface-enhanced Raman scattering (SERS) effect of ZnO and MAPbI(3), the microscopic ZnO/MAPbI(3) heterojunction is investigated, and two main factors affecting the CT process - energy level alignment and film quality - are discussed. Under different conduction band offset (CBO) values, the ZnO/MAPbI(3) heterojunction exhibited evident CT trend changes, observed with the SERS signal of probe molecules. When the precursor ratio of PbI2/MAI was 1.0, the strongest CT was observed with the CBO at 0.14 eV. This work not only provides new information for PSC fabrication but also suggests a role for SERS in sensing the CT process of solar devices.