Inverted Organic Solar Cells Enabled by a ZnO/Organic Electrolyte Dual-Layer Electron Transport Layer with Improved Efficiency and Stability

ZnO as a cathode interface material has been widely used in inverted organic solar cells (I-OSCs). Unfortunately, the existence of inherent surface defects in ZnO hinders further improvement in the efficiency and lifetime of I-OSCs, which is not conducive to clean production and carbon reduction throughout the entire lifecycle. Surface modification is an effective strategy to improve ZnO films. However, the thickness of the surface modification layer reported is generally around 5 nm, hindering large-area fabrication in industrial applications. Herein, we report two small-molecule electrolytes (SMEs) (PMABr and PMABr-OH) as surface modification layers to modify the ZnO film. This modification effectively passivates the oxygen vacancy defects in the ZnO film and synchronously ameliorates the efficiency and stability of photovoltaic devices. In addition, the surface modification layer can slightly reduce the hydrophilicity of the ZnO film and lower the ultraviolet light intensity. As a result, the I-OSC devices achieved improved efficiency from 15.90 to 17.02% with PMABr-OH-modified ZnO electron transport layers (ETLs). The I-OSC devices with dual-layer ETLs demonstrate better stability than the ZnO reference device. Furthermore, utilizing the ZnO/PMABr-OH dual-layer ETL, thick-film I-OSC devices with thicknesses of surface modification layers ranging from 10 to 35 nm are fabricated, and they present high PCEs of over 16.6%.