报告题目：Acceptor Concentration dependent Exciton Dynamics of narrow band-gap
报告人：Prof. Chan Im
Department of Chemistry, Konkuk University, Seoul, Korea
To achieve intrinsically light-weighted flexible photovoltaic devices, a bulk-heterojunction type active layer with a narrow bandgap polymer is still one of the most important candidates. Therefore, detailed information about the electron transfer efficiency from a photo-excited species on an electron donating polymer to an electron acceptor is an important factor because this is one of the most fundamental quantitative measures to understand the solar power conversion efficiency in particular at the initial stage followed by a primary exciton formation. To obtain this information on an accurate level, wide range acceptor concentration dependent transient absorption spectroscopy with femtosecond laser pulse excitation was performed by using a representative narrow bandgap polymer, commonly known as PTB7. Investigated acceptor concentration range was covered from 0.01 wt% up to 10 wt% in addition to a 0 wt% pristine polymer sample and a sample with a conventional acceptor concentration of 60 wt% being important for high efficiency. From that kinetic data, almost two orders of magnitude faster acceptor induced electron transfer rate constant in addition to the native primary exciton life time of about 100 picoseconds could be extracted. Those data were used to verify the kinetic model and compared with device properties.