Green-light wavelength-selective organic solar cells for agrivoltaics: dependence of wavelength on photosynthetic rate

Abstract

There is a growing demand for the development of novel solar power systems that can simultaneously solve the problems associated with both energy generation and food supply in agriculture. Green-light wavelength-selective organic solar cells (OSCs), whose transmitted blue and red light can be utilized to promote plant growth were recently reported by our group. However, the influence of wavelength variation on the photosynthetic rate in green-light wavelength-selective OSCs remains unclear. In this study, we report on the design and synthesis of new electron-accepting π-conjugated molecules containing cyclopentene-annelated thiophene with a spiro-substituted 2,7-bis(2-ethylhexyl)fluorene (FT) unit (TT-FT-ID) as a green-light wavelength-selective nonfullerene acceptor along with a reference compound TT-T-ID. Photophysical measurements indicate that the introduction of the FT unit leads to an absorption band with a small full width at half maximum in films, leading to the ability to fine-tune the absorption length. Concerning the optimization of the conditions for the fabrication of the active layers, which are composed of a green-light wavelength-selective donor polymer of poly(3-hexylthiophene) (P3HT) and the new acceptors, Bayesian optimization based on Gaussian process regression was applied to minimize the experimental batches. The green-light wavelength-selective factor (S_G) and the PCEs in the green-light region (PCE-GR) of the P3HT:TT-FT-ID-based device were determined to be 0.52 and 8.6%, respectively, which are higher values than those of the P3HT:TT-T-ID blend film. The P3HT:TT-FT-ID blend film increased the photosynthetic rate of green pepper compared to that of the P3HT:TT-T-ID blend film. These results indicate that the fine-tuning of the absorbance required for crop growth is an important issue in developing green-light wavelength-selective OSCs for agrivoltaics.