Significantly Enhancing the Efficiency of a New Light-Harvesting Polymer with Alkylthio naphthyl Substituents Compared to Their Alkoxyl Analogs

Gongyue Huang, Jun Zhang, Nergui Uranbileg, Weichao Chen, Huanxiang Jiang, Hua Tan, Weiguo Zhu, Renqiang Yang

Index: 10.1002/aenm.201702489

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Abstract

Abstract In this work, a new benzo[1,2-b:4,5-b′]dithiophene (BDT) building block containing alkylthio naphthyl as a side chain is designed and synthesized, and the resulting polymer, namely PBDTNS-BDD, shows a lower HOMO energy level than that of its alkoxyl naphthyl counterpart PBDTNO-BDD. An optimized photovoltaic device using PBDTNS-BDD as a donor exhibits power conversion efficiencies (PCE) of 8.70% and 9.28% with the fullerene derivative PC71BM and the fullerene-free small molecule ITIC as acceptors, respectively. Surprisingly, ternary blend devices based on PBDTNS-BDD and two acceptors, namely PC71BM and ITIC, shows a PCE of 11.21%, which is much higher than that of PBDTNO-BDD based ternary devices (7.85%) even under optimized conditions. Ternary blend devices containing a new building block show much better power conversion efficiencies than their corresponding binary counterparts. These new building blocks contain alkylthio naphthyl as a side chain. Blending with two acceptors, PC71BM and ITIC, results in PBDTNS-BDD devices with a power conversion efficiency of 11.21%, which is much higher than that of the PBDTNO-BDD (7.85%) analogue under optimized conditions.