Photoinduced Slowdown of Charge Carrier Transport and Phonon Emission in Conjugated Polymers

Abstract

In a real bulk heterojunction polymer solar cell, once the photoactive polymer layer undergoes photoexcitation, the formed electron–hole pair (or exciton) diffuses to the fabricated heterojunction to be dissociated, and then the resultant charge carriers move toward the cathode and anode. During the negative polaron transport, the external light field excites the polaron and makes it transport slowly where the excitation selects three localized phonon modes with even parity and higher frequency, not only greatly deepening the local distortion along alternating bonds but also leading to blue shift in the infrared phonon spectrum. It is furthermore discovered that the slowdown of the charged polaron’s velocity is contributed by the occurrence of the phonon modes and the blue shift of the phonon spectrum. Controlling the phonon modes and the frequency blue shift of the phonon spectrum in a composite conjugated polymer solar cell presents an opportunity for modifying the properties of polymer solar cells.