Abstract
A long-lived hot carrier population is critical in order to develop working hot carrier photovoltaic devices with efficiencies exceeding the Shockley–Queisser limit. Here, we report photoluminescence from hot-carriers with unexpectedly long lifetime (a few ns) in formamidinium tin triiodide. An unusual large blue shift of the time-integrated photoluminescence with increasing excitation power (150 meV at 24 K and 75 meV at 293 K) is displayed. On the basis of the analysis of energy-resolved and time-resolved photoluminescence, we posit that these phenomena are associated with slow hot carrier relaxation and state-filling of band edge states. These observations are both important for our understanding of lead-free hybrid perovskites and for an eventual future development of efficient lead-free perovskite photovoltaics.
Highlights
A long-lived hot carrier population is critical in order to develop working hot carrier photovoltaic devices with efficiencies exceeding the Shockley–Queisser limit
Films of FASnI3 were prepared on indium tin oxide (ITO) covered glass substrates by spin coating
The first is the radiative excitonic recombination. This possibility is readily exempted at room temperature, because excitonic features are not observed in the absorption spectrum, suggesting a very small exciton binding energy for this material[35]
Summary
A long-lived hot carrier population is critical in order to develop working hot carrier photovoltaic devices with efficiencies exceeding the Shockley–Queisser limit. Due to their narrower optical band gap (1.3 eV for MASnI3 and 1.32 eV for CsSnI3)[17,18], and broader solar spectrum absorption, the tin perovskites are potentially better candidates for high performance photovoltaic devices These effective light harvesting materials have been recently employed in single junction solar cells with reported power conversion efficiencies larger than 8%19 and 9% in our group[20]. It is known that when a semiconductor is excited with photons of energy higher than the band gap, hot carriers are generated and their excess energy is dissipated via phonon emission till they thermalize to the bottom of the band This is a major loss channel in photovoltaics, and is partially responsible for the Shockley–Queisser efficiency limit. Insight into the hot carrier relaxation and the charge recombination mechanism in FASnI3 films are obtained by studying the energy-resolved and time-resolved PL (TRPL)
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