Menke S Matthew, Cheminal Alexandre, Conaghan Patrick, Ran Niva A, Greehnam Neil C, Bazan Guillermo C, Nguyen Thuc-Quyen, Rao Akshay, Friend Richard H
Department of Physics, Cavendish Laboratory, University of Cambridge, 19 JJ Thompson Avenue, Cambridge, CB3 0HE, UK.
Center for Polymers and Organic Solids, University of California, Santa Barbara, Santa Barbara, CA, 93106, USA.
Nat Commun. 2018 Jan 18;9(1):277. doi: 10.1038/s41467-017-02457-5.
Donor-acceptor organic solar cells often show low open-circuit voltages (V ) relative to their optical energy gap (E ) that limit power conversion efficiencies to ~12%. This energy loss is partly attributed to the offset between E and that of intermolecular charge transfer (CT) states at the donor-acceptor interface. Here we study charge generation occurring in PIPCP:PCBM, a system with a very low driving energy for initial charge separation (E -E ~ 50 meV) and a high internal quantum efficiency (η ~ 80%). We track the strength of the electric field generated between the separating electron-hole pair by following the transient electroabsorption optical response, and find that while localised CT states are formed rapidly (<100 fs) after photoexcitation, free charges are not generated until 5 ps after photogeneration. In PIPCP:PCBM, electronic disorder is low (Urbach energy <27 meV) and we consider that free charge separation is able to outcompete trap-assisted non-radiative recombination of the CT state.
供体-受体有机太阳能电池相对于其光学能隙（E）通常表现出较低的开路电压（V），这将功率转换效率限制在约12%。这种能量损失部分归因于E与供体-受体界面处分子间电荷转移（CT）态的能隙之间的偏移。在此，我们研究了在PIPCP:PCBM中发生的电荷产生过程，该体系具有极低的初始电荷分离驱动能量（E - E ~ 50 meV）和较高的内量子效率（η ~ 80%）。我们通过跟踪瞬态电吸收光学响应来追踪分离的电子-空穴对之间产生的电场强度，发现虽然在光激发后迅速（<100 fs）形成了局域化的CT态，但直到光生5 ps后才产生自由电荷。在PIPCP:PCBM中，电子无序度较低（乌尔巴赫能量<27 meV），我们认为自由电荷分离能够胜过CT态的陷阱辅助非辐射复合。
