Order enables efficient electron-hole separation at an organic heterojunction with a small energy loss.

ABSTRACT: Donor-acceptor organic solar cells often show low open-circuit voltages (V OC) relative to their optical energy gap (E g) that limit power conversion efficiencies to ~12%. This energy loss is partly attributed to the offset between E g and that of intermolecular charge transfer (CT) states at the donor-acceptor interface. Here we study charge generation occurring in PIPCP:PC61BM, a system with a very low driving energy for initial charge separation (E g-E CT?~?50?meV) and a high internal quantum efficiency (? IQE?~?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:PC61BM, 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.

SUBMITTER: Menke SM 

PROVIDER: S-EPMC5773693 | biostudies-other | 2018 Jan

REPOSITORIES: biostudies-other