A simple strategy passivating ZnO electron transport layers for realizing high efficiency in organic solar cells

Abstract

Sol–gel processed ZnO films are widely used as electron transport layers (ETLs) in organic solar cells (OSCs). However, defects caused by COOH, OH, and vacancies of oxygen in ZnO ETLs are harmful for electron extraction and transport processes in OSCs. Here, a simple and effective strategy is reported to passivate free OH via hydrogen bond of HO…NH2. A small molecule of biuret is introduced into ZnO precursor as an additive to form ZnO films. The hydrogen bond of HO…NH2 is confirmed by XPS and FT-IR in this study, which passivates traps originated from free OH. The passivated ZnO ETLs exhibit better morphology and higher electron mobility than pristine ZnO ETLs. In OSCs with fullerene and non-fullerene light absorbers, the cells with biuret-doped ZnO ETLs obtain improved power conversion efficiency (PCE), which prove the generality of biuret doped ZnO ETLs. Eventually, a maximal PCE of 18.19 % is obtained when PM6:L8-BO is selected as light absorber. Furthermore, the contributions of biuret are discussed in this work.