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:PC71BM 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.