Precursor Engineering to Reduce Processing Temperature of ZnO Films for Flexible Organic Solar Cells

Abstract

AbstractSol‐gel‐derived ZnO is one of the most widely used electron‐transport layers in inverted organic solar cells. The sol‐gel ZnO precursor consists of zinc acetate dehydrate (ZAH) and ethanolamine dissolved in 2‐methoxyethanol, where ethanolamine chelates with ZAH, which helps ZAH dissolve in the 2‐methoxyethanol. However, an annealing temperature above 120 °C is required to convert the complexes into ZnO. High temperatures are incompatible with flexible plastic substrates such as polyethylene terephthalate. In this work, we report an amine‐free recipe consisting of ZAH in methanol to prepare ZnO films. The complex formed in the amine‐free precursor solution is methanol‐solvated ZAH, which is simpler than that of the amine‐containing precursor solution. The temperature required for converting the precursor complex into ZnO was reduced to 90 °C for the amine‐free recipe. Low‐temperature‐processed ZnO can function efficiently as an electron‐transport layer in both rigid and flexible inverted nonfullerene solar cells.