Understanding electron-phonon interaction in solution-processed photovoltaic materials

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Chinese explanation / 中文解读

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Original abstract

The modulation of charge carrier dynamics by lattice motion is an inherent characteristic of photovoltaic materials. Increasing research interest in understanding and controlling this complex interaction has continuously grown for the past few years with the aim of further improving solar cells’ device performance. This review analyses recent studies on solution-processed organic polymers, hybrid perovskites, and quantum dots to elucidate the direct consequences of lattice dynamics on material photophysics. Current literature increasingly indicates the need to alleviate electron-phonon interactions (EPI) since such mitigation can extend the hot carrier cooling times and reduce non-radiative recombination. It can likewise suppress polaron formation that would otherwise increase effective mass and decrease mobility, and can stabilize the molecular structures that could limit bandgap renormalization. However, many investigations to date have employed phenomenological models that treat phonons as collective molecular motions, which often leads to speculative interpretations of ambiguous data. To accurately quantify EPI effects, it is essential to examine specific lattice modes using coherent ultrafast transient techniques. For instance, in ternary organic polymer solar cells, short-lived vibronic coherence has been shown to promote charge separation, whereas in single-crystal hybrid perovskites, picosecond quantum beating extends carrier lifetimes. In CdSe quantum dots, vibronic coherences between core excitons and ligand vibrations regulate the rates and yields of competing photophysical processes. We therefore highlight the necessity of advanced ultrafast spectroscopy techniques as crucial tools for directly probing this phenomenon to enable deeper insights and ascertain the precise conditions and time scales at which EPI loses its beneficial role.

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