Double anchor indolo[3,2-b]indole-derived metal-free dyes with extra electron donors as efficient sensitizers for dye-sensitized solar cells

Abstract

Two new di-acceptors metal-free organic dyes based on indolo[3,2-b]indole donor backbone with extra electron donors were designed, synthesized, and applied for dye-sensitized solar cells (DSSCs). In this study, the effect of the additional donors was investigated by the replacement of the typical N-alkyl side chain using methoxyphenyl (dye 1) and hexyloxyphenyl (dye 2) as secondary donor groups. Molecular dyes-based di-anchoring models enhanced the significant interaction between sensitizing dyes and the TiO₂ surface as well as yielded better light-harvesting efficiency, compared to the familiar core indolo-indole donor. Under global standard condition 1.5 AM, dye 2-based cells show an enhanced overall conversion efficiency of 7.86% while that of the standard commercial N719-based cells is 8.08%. Therefore, the double anchor indolo[3,2-b]indole with additional donors is a promising candidate for efficient DSSCs.