Affiliation: | 1. Department of Chemistry, City University of Hong Kong Kowloon, Hong Kong, 999077 China;2. Institute of Clean Energy, City University of Hong Kong Kowloon, Hong Kong, 999077 China Department of Material Science & Engineering, City University of Hong Kong Kowloon, Hong Kong 999077, China;3. Department of Physics, Chemistry and Biology (IFM), Linköping University, Linköping, 58183 Sweden;4. Department of Materials Science & Engineering, University of Washington, Seattle, Washington, 98195 United States;5. State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an, 710049 P. R. China;6. Department of Chemistry, City University of Hong Kong Kowloon, Hong Kong, 999077 China Institute of Clean Energy, City University of Hong Kong Kowloon, Hong Kong, 999077 China |
Abstract: | Organic photovoltaics (OPV) are one of the most effective ways to harvest renewable solar energy, with the power conversion efficiency (PCE) of the devices soaring above 19 % when processed with halogenated solvents. The superior photocurrent of OPV over other emerging photovoltaics offers more opportunities to further improve the efficiency. Tailoring the absorption band of photoactive materials is an effective way to further enhance OPV photocurrent. However, the field has mostly been focusing on improving the near-infrared region photo-response, with the absorption shoulders in short-wavelength region (SWR) usually being neglected. Herein, by developing a series of non-fullerene acceptors (NFAs) with varied side-group conjugations, we observe an enhanced SWR absorption band with increased side-group conjugation length. The underpinning factors of how molecular structures and geometries improve SWR absorption are clearly elucidated through theoretical modelling and crystallography. Moreover, a clear relationship between the enhanced SWR absorption and reduced singlet-triplet energy gap is established, both of which are favorable for the OPV performance and can be tailored by rational structure design of NFAs. Finally, the rationally designed NFA, BO-TTBr, affords a decent PCE of 18.5 % when processed with a non-halogenated green solvent. |