Hydroquinone redox mediator enhances the photovoltaic performances of chlorophyll-based bio-inspired solar cells
Shengnan Duan, Chiasa Uragami, Kota Horiuchi, Kazuki Hino, Xiaofeng Wang, Shin‐ichi Sasaki, Hitoshi Tamiaki, Hideki Hashimoto
Abstract
Abstract Chlorophyll (Chl) derivatives have recently been proposed as photoactive materials in next-generation bio-inspired solar cells, because of their natural abundance, environmental friendliness, excellent photoelectric performance, and biodegradability. However, the intrinsic excitation dynamics of Chl derivatives remain unclear. Here, we show sub-nanosecond pump–probe time-resolved absorption spectroscopy of Chl derivatives both in solution and solid film states. We observe the formation of triplet-excited states of Chl derivatives both in deoxygenated solutions and in film samples by adding all-trans-β-carotene as a triplet scavenger. In addition, radical species of the Chl derivatives in solution were identified by adding hydroquinone as a cation radical scavenger and/or anion radical donor. These radical species (either cations or anions) can become carriers in Chl-derivative-based solar cells. Remarkably, the introduction of hydroquinone to the film samples enhanced the carrier lifetimes and the power conversion efficiency of Chl-based solar cells by 20% (from pristine 1.29% to 1.55%). This enhancement is due to a charge recombination process of Chl-A + /Chl-D – , which is based on the natural Z-scheme process of photosynthesis.