Highly efficient inverted polymer solar cells using aqueous ammonia processed ZnO as an electron selective layer

The authors demonstrate a simple method to deposit solution-processable ZnO thin film by directly dissolving the ZnO powder into aqueous ammonia. ZnO film casting from its aqueous ammonia solution (a-ZnO) is used successfully as an electron selective layer in poly(3-hexylthiophene) and indene-C₆₀ bisadduct (IC₆₀BA) based heterojunction solar cells with improved power conversion efficiency (PCE) compared with that using conventional sol–gel based ZnO (c-ZnO). The improved PCE is mainly attributed to an increase of short-circuit current density owing to the better transmittance of a-ZnO than that of c-ZnO in the absorption range of IC₆₀BA, and efficient electron extraction at cathode. In addition, no additional by-products originated from the organic solvents are introduced as like in sol–gel based ZnO films.