Electron extraction layer based on diketopyrrolopyrrole/isoindigo to improve the efficiency of inverted perovskite solar cells

Diketopyrrolopyrrole (DPP) and isoindigo (ISO) moieties have been widely studied in organic optoelectronic materials, while they have been rarely explored as electron transporting materials in perovskite solar cells (PSCs). In this paper, two organic molecules, tetraphenylethylene-diketopyrrolopyrrole (TPE-DPP4) and tetraphenylethylene-isoindigo (TPE-ISO4), were synthesized and successfully used in inverted PSCs. Cyclic voltammetry measurement revealed the matched energy levels of the TPE- based interlayers with perovskite materials. Steady-state photoluminescence (PL) spectra, time-resolved PL decay results and electrochemical impedance spectroscopy (EIS) indicate the enhanced electron extraction and electron-transporting ability after introducing the TPE-DPP4/TPE-ISO4-based interlayer in PSCs. As a result, devices with TPE-DPP4 and TPE-ISO4 interlayers exhibit high power conversion efficiencies (PCEs) of 18.44% and 18.19%, respectively, and notably, the FF values are as high as 80%. The standard device without an interlayer was also measured, showing an inferior PCE of 16.87%. Therefore, TPE-DPP4 and TPE-ISO4 can work as efficient interfacial materials for improving electron transfer, and finally for enhancing the photovoltaic performance in inverted PSCs. As far as we know, this is the first report on the DPP/ISO-based interfacial layer in perovskite solar cells. The results in this work also demonstrate the great potential of DPP or ISO-based n-type materials for application in PSCs.