Doped/Undoped A1-A2 Typed Copolymers as ETLs for Highly Efficient Organic Solar Cells

摘要

The electron transport layer (ETL) is a critical component in achieving highdevice performance and stability in organic solar cells. Conjugatedpolyelectrolytes (CPEs) have become an attractive alternative due tofilm-forming properties and ease of preparation. However, p-type CPEsgenerally exhibit poor charge mobility and conductivity, incorporation ofelectron-withdrawing units forming alternated D-A conjugated backbone canmake up for these deficiencies. Herein, the ratio of electron withdrawingmoieties are further increased and two poly(A1-alt-A2) typed PIIDNDI-Br andPDPPNDI-Br based on the combination of naphthalene diimide (NDI) withisoindigo (IID) or diketopyrrolopyrrole (DPP) via direct arylationpolycondensation are synthesized. These CPEs possess excellent alcoholsolubility, a suitable lowest unocuppied molecular orbital energy level, andwork function tunability. Surprisingly, the incorporation of IID and DPP unitsgenerate distinct self-doping behaviors, which are confirmed by UV–visabsorption and ESR spectra. However, no matter doped or undoped, bothCPEs present better charge-transporting properties and conductivity whenutilized as ETLs. The PIIDNDI-Br and PDPPNDI-Br display good universalcompatibility with the blend of PM6:Y6 and PM6:L8-BO, and PCEs of 18.32and 18.36 are obtained, respectively, which also present excellent storagestability. In short, the combination of two different acceptors demonstrates anefficient strategy to design highly efficient ETLs for high performancephotovoltaic devices.