Channeling Exciton Migration into Electron Transfer in Formamidinium Lead Bromide Perovskite Nanocrystal/Fullerene Composites

Abstract

Hydrophobic-capped nanocrystals of formamidinium lead bromide (FAPbBr3) perovskite (PNC) show bright and stable fluorescence in the solution and thin film states. When compared with isolated PNCs in a solution, close-packed PNCs in a thin film show extended fluorescence lifetime (ca 4.2 µs), which is due to hopping or migration of photogenerated excitons among PNCs. Both fluorescence quantum efficiency and lifetime decrease in a PNC thin film doped with C60, which is attributed to channeling of exciton migration into electron transfer to fullerenes. On the other hand, quenching of fluorescence intensity of a PNC solution isn't accompanied by any change in fluorescence lifetime, indicating static electron transfer to C60 adsorbed onto the hydrophobic surface of individual PNCs. Exciton migration among close-packed PNCs and electron transfer to C60 places C60-doped PNC thin films among cost-eff ective antenna systems for solar cells.Metal halide perovskites have emerged into a class of promising materials for top 10 future technologies such as solar cells, which is owing to their distinctive optical and electronic properties and cost-effective production. Recent reports show solar photon to electricity conversion efficiency of perovskite solar cells exceeds 20%, keeping the upper limit open to further research, which, on the other hand, hits the roof for silicon photovoltaics. 1 The commendable optical and electronic properties of perovskites make them also useful for several other optical and electronic devices such as light-emitting diodes, lasers, photodetectors, sensors and memory devices. 2 Besides the straightforward preparation and applications of perovskite films, very recently, hybrid PNCs have become popular with great research interest and technological relevance. 3 PNCs exhibit intense fluorescence due to quantum confinement effect which is easily tuned by band-gap engineering and chemical composition 4 and show great promise when compared with perovskite films. 5 Addressing fundamental photophysical properties of PNCs in combination with other materials calls for exploration, and is expected to further the applications of PNCs in LEDs and solar cells. Photoinduced electron transfer (PET) is the fundamental process in natural and artificial photosynthesis. 6 Recently, electron transfer studies in perovskite-based electron donoracceptor systems receive great momentum, which is owing to their potential application in solar cell technology. For example, Grätzel et al. revealed ultrafast electron transfer from photoexcited perovskite to mesoporous titanium dioxide, leading to efficient charge separation. 7 In a subsequent report, Sunderström et al. pinpointed the time scale and mechanism of electron transfer from perovskite to an organic acceptor molecule. 8 PNCs have been explored in electron transfer to classical acceptors such as benzoquinone, 9 phenothiazine 9 and perylene. 10 Recent studies by Huang et al. and Sargent et al. show improved stability and photocurrent response for solar cells based ...

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“…Following this report, several studies done by various groups suggest that hybrid perovskites in nanocrystal form are suitable for most of the above‐mentioned applications . In this context, very recently, we have demonstrated the excellent energy migration properties of these materials . We have also illustrated the use of PNCs for memory device applications and as sensors for the detection of explosives .…”

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