Abstract
Multiple exciton generation (MEG) or carrier multiplication, a process that spawns two or more electron–hole pairs from an absorbed high-energy photon (larger than two times bandgap energy Eg), is a promising way to augment the photocurrent and overcome the Shockley–Queisser limit. Conventional semiconductor nanocrystals, the forerunners, face severe challenges from fast hot-carrier cooling. Perovskite nanocrystals possess an intrinsic phonon bottleneck that prolongs slow hot-carrier cooling, transcending these limitations. Herein, we demonstrate enhanced MEG with 2.25Eg threshold and 75% slope efficiency in intermediate-confined colloidal formamidinium lead iodide nanocrystals, surpassing those in strongly confined lead sulfide or lead selenide incumbents. Efficient MEG occurs via inverse Auger process within 90 fs, afforded by the slow cooling of energetic hot carriers. These nanocrystals circumvent the conundrum over enhanced Coulombic coupling and reduced density of states in strongly confined nanocrystals. These insights may lead to the realization of next generation of solar cells and efficient optoelectronic devices.
Highlights
Multiple exciton generation (MEG) or carrier multiplication, a process that spawns two or more electron–hole pairs from an absorbed high-energy photon, is a promising way to augment the photocurrent and overcome the Shockley–Queisser limit
We report that intermediate-confined formamidinium lead iodide (FAPbI3) NCs, possessing an intrinsic phonon bottleneck, transcend the above challenges as an emerging class of NCs for enhanced MEG
Cubic-shaped colloidal FAPbI3 NCs prepared through hot-injection synthesis were size-segregated (7.5–13 nm edge length) using different centrifugation speeds and ligands
Summary
Multiple exciton generation (MEG) or carrier multiplication, a process that spawns two or more electron–hole pairs from an absorbed high-energy photon (larger than two times bandgap energy Eg), is a promising way to augment the photocurrent and overcome the Shockley–Queisser limit. Efficient MEG occurs via inverse Auger process within 90 fs, afforded by the slow cooling of energetic hot carriers These nanocrystals circumvent the conundrum over enhanced Coulombic coupling and reduced density of states in strongly confined nanocrystals. Semiconductor nanostructures, especially strongly confined nanocrystals (NCs)[6,7,8,9,10,11,12,13,14,15], were projected to exhibit enhanced MEG due to relaxed momentum conservation[16], enhanced Coulomb coupling[17] and prolonged hot carrier cooling arising from the predicted phonon bottleneck effect under strong quantum confinement[18]. These insights may lead to the realization of a generation of solar cells and efficient lightharvesting devices
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