Highly efficient organic solar cells enabled by a porous ZnO/PEIE electron transport layer with enhanced light trapping

In this study, a porous inorganic/organic (ZnO/PEIE, where PEIE is polyethylenimine ethoxylated) (P-ZnO) hybrid material has been developed and adopted in the inverted organic solar cells (OSCs). The P-ZnO serving as the electron transport layer (ETL) not only presents an ameliorative work function, but also forms the cratered surface with increased ohmic contact area, revealing suppressed charge recombination and enhanced charge extraction in devices. Particularly, P-ZnO-based OSCs show improved light trapping in the active layer compared with ZnO-based ones. The universality of P-ZnO serving as ETL for efficient OSCs is verified on three photovoltaic systems of PBDB-T/DTPPSe-2F, PM6/Y6, and PTB7-Th/PC 71 BM. The enhancements of 8% in power conversion efficiency (PCE) can be achieved in the state-of-the-art OSCs based on PBDB-T/DTPPSe-2F, PM6/Y6, and PTB7-Th/PC 71 BM, delivering PCEs of 14.78%, 16.57%, and 9.85%, respectively. Furthermore, a promising PCE of 14.13% under air-processed condition can be achieved for PZnO/PBDB-T/DTPPSe-2F-based OSC, which is among the highest efficiencies reported for air-processed OSCs in the literature. And the P-ZnO/PBDB-T/DTPPSe-2F-based device also presents superior long-term storage stability whether in nitrogen or ambient air-condition without encapsulation, which can maintain over 85% of its initial efficiency. Our results demonstrate the great potential of the porous hybrid PZnO as ETL for constructing high-performance and air-stable OSCs.