engleski

Photoinduced charge transfer in a conjugated polymer/MoS2 bulk heterojunction

Bulk heterojunction solar cells consisting of a conjugated polymer blended with an electron acceptor material, such as C60, provide the potential for versatile, low-cost photovoltaics. If the two materials are well dispersed within each other, photogenerated excitons on the polymer, with a typical diffusion radius of 10-20 nm, can efficiently reach an interface to the electron acceptor moiety, where they dissociate. We assess the possibility of using micron-size, few-layer MoS2 flakes as an innovative electron acceptor material. Compared to C60, their absorption spectrum is better adapted to the sun spectrum, so they can contribute also to the photogeneration of excitons, not only their dissociation. They also provide higher exciton and charge mobilities, and HOMO and LUMO levels favorable for charge transfer. We study the exciton photogeneration, migration and dissociation on both moieties of a P3HT: MoS2 blend in the time domain using femtosecond pump-probe spectroscopy with 50 fs resolution. We photoexcite the samples at 3.1 eV, well above the HOMO-LUMO gap of both materials and probe the photoexcitation dynamics with a broad band probe pulse covering a spectral range of 450 – 750 nm. We will present a comprehensive scheme of the photoexcitation dynamics in this blend system. In particular, the optical signature of a charge carrier on MoS2 has not been observed previously and is of vital importance for further spectroscopic study of MoS2 itself. By studying different blend ratios we can rapidly assess the best mixture for actual solar cells without the need for statistical evaluation of other processing parameters in the solar cell fabrication.

solar cells; P3HT: MoS2 blend; femtosecond pump-probe spectroscopy; photoexcitation dynamics

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