ZnO Nanorods: An Advanced Cathode Buffer Layer for Inverted Perovskite Solar Cells

Advanced cathode buffer layers (CBLs) with high power conversion efficiency (PCE) and optimized electron collection were developed for inverted perovskite solar cells (PSCs). ZnO nanorods (ZnO-NRs) with 30–40 nm diameter and <1 μm length were prepared via a surfactant-assisted hydrothermal regime and mixed with bathocuproine (BCP) to form (ZnO-NRs/BCP) as a CBL composite, which was used as the base to fabricate planar PSCs (p–i–n) with a device structure of (indium tin oxide /PEDOT:PSS/CH3NH3PbI3–xClx/PC61BM/CBLs/Ag). Compared to a single layer of ZnO-NRs or BCP, the present ZnO-NR/BCP composite has demonstrated a compact, defectless thin film, enhanced long-term stability, and better coverage on the perovskite/PC61BM surface. Also, the interface charge recombination was reduced, and device performance was improved by employing such a composite layer with the ZnO-NR’s assistance. The PCE of a ZnO-NR/BCP-based device was estimated to be 18.13%, which is higher than the values of the single-layer ZnO-NR-based (16.55%) or BCP-based (15.17%) devices. Our work demonstrated the promising application of ZnO-NRs/BCP as a CBL composite with almost no degradation detected for PSCs. This composite can provide interface property stabilization and enhance the performance stability of the PSCs.