Semisynthetic Chlorophyll Derivatives Toward Solar Energy Applications

Plenty of thin‐film solar cell technologies using organic materials have been developed to alleviate energy shortages. As developing devices for solar energy applications, artificial photosynthesis is a trend inspired from natural photosynthesis. Although the sophisticated system that exists in nature is fascinating, the development of photovoltaic devices focusing on the usage of natural chlorophylls has been quite limited, compared with the application of other counterparts such as artificial porphyrins or phthalocyanines. Herein, the development of semisynthetic chlorophyll derivatives as functional materials for solar cells are focused on. (Bacterio)chlorins possessing a carboxylic acid moiety as a binding site to semiconductors are synthesized to improve the efficiencies of dye‐sensitized solar cells, which are now leading to another application: photocatalysts for hydrogen evolution. In contrast, derivatives without a carboxy group can be applied to organic solar cells. As for the application for perovskite solar cells, self‐assembling aggregates of a kind of derivatives are proven to be suitable as hole‐transporting materials. In addition, a new type of solid‐state biosolar cells is proposed, in which chlorophyll derivatives act solely as the photoactive materials. This Report can enlarge the scope of advanced functional materials in the field of solar energy applications.