A New Alcohol‐Soluble Polymer PFN‐ID as Cathode Interlayer to Optimize Performance of Conventional Polymer Solar Cells by Increasing Electron Mobility

A new alcohol‐soluble polymer PFN‐ID is successfully synthesized by combining N , N ‐di(2‐ethylhexyl)‐6,6′‐dibromoisoindigo and an amino‐containing fluorene subunits, and applied to polymer solar cells (PSCs) with PTB7‐Th:PC 71 BM as an active layer. The n‐type backbone of the PFN‐ID improves electron transfer performance and thus optimizes device performance. The PSCs with PFN‐ID as cathode interfacial layers (CILs) have significantly improved compared to the device without the interface layer, especially the optimum power conversion efficiency (PCE) of PSCs reaches up to 9.24%, which is 1.62 times higher than that of devices without CILs. The I–V curves show that the introduction of the n‐type backbone leads to a significant increase in the conductivity of PFN‐ID compared to PFN. The UV photoelectron spectroscopy and Mott–Schottky curves further confirm that PFN‐ID can decrease the work function of Al electrode, and increase its built‐in potential, giving higher open‐circuit voltage. The resulting conventional PSCs using PFN‐ID as cathode interlayer achieve high photovoltaic performance, and the research results can provide a new strategy for the advancement of PSCs.