Increasing Photoinduced Interfacial Charge Separation Lifetime through Control of the Twist Angle in the Donor Region of Carbazole-Based Dyes

Abstract

Molecular-based optoelectronic devices and photocatalytic systems often rely on the photogeneration of charge-separated states. Increasing the longevity of charge-separated states allows for access to higher-functioning devices and systems by extending the length of time before subsequent events are required to occur. In dye-sensitized solar cells (DSC), back electron transfer (BET) from a reduced metal oxide to an oxidized dye is an unproductive electron transfer pathway that determines the charge-separated state lifetime. This study seeks to limit BET by lowering the electronic coupling of the donor and acceptor in the charge-separated excited state through the use of sterics. A series of three dyes with a varying number of methyl groups (0–2) on the donor were studied using nanosecond transient absorption spectroscopy (nsTAS) to compare rates of BET. Novel dye CC10 (1 Me), designed with one methyl group in the donor region connected to the acceptor, was found to lower back electron transfer rates by 22× compared to the control dye, CC12 (0 Me), with no methyl groups.