Alkyl chain engineering on tetraphenylethylene-diketopyrrolopyrrole-based interfacial materials for efficient inverted perovskite solar cells

Abstract A series of tetraphenylethylene-diketopyrrolopyrrole (TPE-DPP) derivatives with different alkyl chains were synthesized and characterized. The effects of alkyl chains on the electronic property of these compounds and the performance of perovskite solar cells (PSCs) were investigated. Cyclic voltammetry results suggest that different alkyl chains have little influence on the molecular energy levels of these TPE-DPP derivatives. AFM (atomic force microscopy) images indicate that among the derivatives studied, TPE-DPP derivative with 2-butyloctyl (TPE-DPPC12) shows the most smooth surface morphology on top of the perovskite layer, ensuring a good charge selective contact. Time-resolved photoluminescence (PL) spectra indicate that the TPE-DPPC12 shows the best electron extraction ability. As a result, the device with TPE-DPPC12 interlayer exhibited an average power conversion efficiency (PCE) of 18.37%, corresponding to an increase of 17% relative to the control device (16.37%). In addition, considering the hydrophobic nature of TPE-DPPC12, the ambient stability of inverted PSCs incorporating the TPE-DPPC12 interlayer is also improved. This study provides an effective design strategy for electron extraction materials to achieve highly-efficient PSCs with improved stability.