Multiple exciton generation in tin-lead halide perovskite nanocrystals for photocurrent quantum efficiency enhancement

Multiple exciton generation (MEG), the generation of multiple electron-hole pairs from a single high-energy photon, can enhance the photoconversion efficiency in several technologies including photovoltaics, photon detection and solar-fuel production(1-6). However, low efficiency, high photon-energy threshold and fast Auger recombination impede its practical application(1,7). Here we achieve enhanced MEG with an efficiency of up to 87% and photon-energy threshold of two times the bandgap in highly stable, weakly confined formamidinium tin-lead iodide perovskite nanocrystals (FAPb(1-x)Sn(x)I(3) NCs; x <= 0.11). Importantly, an MEG-driven increment in the internal photocurrent quantum efficiency exceeding 100% with a low threshold is observed in such NC-sensitized photoconductors under ultraviolet-light illumination. The MEG enhancement mechanism is found to be mediated by the slower cooling and reduced trapping of hot carriers above the MEG threshold after the partial substitution of Pb by Sn. Our findings corroborate the potential importance of narrow-bandgap perovskite NCs for the development of optoelectronics that could benefit from MEG.

Automated summary

The study demonstrates enhanced multiple exciton generation in formamidinium tin-lead iodide perovskite nanocrystals, achieving high photoconversion efficiency and reducing photon-energy threshold. By observing internal photocurrent quantum efficiency exceeding 100% and a lower threshold in such materials, the mechanism of MEG enhancement is found to be mediated by slower cooling and reduced trapping of hot carriers above the MEG threshold.