Simultaneous realization of bulk and interface regulation based on 2,4-diamino-6,7-diisopropylpteridine phosphate for efficient and stable inverted perovskite solar cells

Due to strict restrictions on the solubility and solvent choice, it is challenging to achieve an efficient solution-processed cathode interface material for inverted perovskite solar cells (PSCs). Herein, a simple and facile solution-processed interface strategy is proposed based on 2,4-diamino-6,7-diisopropylpteridine phosphate (DPP) to overcome bulk and interface recombination loss issues in inverted PSCs. The performances of the materials, interfaces, and the devices were systemically investigated. The results show that DPP exists at the fullerene/cathode interface and also diffuses throughout the whole perovskite/fullerene heterojunction, which results in the simultaneous realization of bulk and interface regulation. The interface energy mismatch between the (6,6)-phenyl-C61 butyric acid methyl ester (PCBM) and Ag interface, the defect-assisted recombination energy loss, and the residual stress of the perovskite film are all improved by DPP introduction. The power conversion efficiency (PCE) of the devices with DPP is enhanced by 33.49% compared to that of the control devices without DPP. The highest PCE of 20.17% and a hysteresis index of 1.80% were achieved with DPP, which is superior to that of the devices with a conventional bathocuproine (BCP) cathode interface layer. Owing to the DPP introduction, the thermal stability (85 °C in N2) is greatly enhanced and T80 (the time required for the PCE decay to 80% of its initial value) reaches up to 247 h, while T80 of the control devices is only 14 h. This work provides an extremely simple and unique strategy to simultaneously realize bulk and interface regulation with only one material for the construction of efficient and stable inverted PSCs.