Hot photons and open-circuit voltage in molecular absorbers

Abstract

Hot carrier solar cells have attracted interest for many years. Although no working exemplars exist today, the challenges to overcome have become clearer and a substantial research effort has been underway with a focus on inorganic semiconductors, including quantum wells. In this paper we propose a novel strategy to potentially exploit hot photons, based on organic absorbers. Our approach, when combined with photon management structures similar to photonic fluorescent collectors (FCs), can potentially enhance the efficiency of complete photovoltaic devices. We present a characterisation method of FCs by evaluating the chemical potential and temperature of the emitted fluorescence photon flux. We report on observation of temperatures of the emitted photon flux well above the ambient temperature, indicating the presence of hot photons. We propose a theoretical background to describe how excess thermal energy carried by hot photons can be exploited to increase the chemical potential of the photon flux which is closely related to the open-circuit voltage of the solar cell.

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