Abstract
Hot-carrier solar cells can overcome the Shockley-Queisser limit by harvesting excess energy from hot carriers. Inorganic semiconductor nanocrystals are considered prime candidates. However, hot-carrier harvesting is compromised by competitive relaxation pathways (for example, intraband Auger process and defects) that overwhelm their phonon bottlenecks. Here we show colloidal halide perovskite nanocrystals transcend these limitations and exhibit around two orders slower hot-carrier cooling times and around four times larger hot-carrier temperatures than their bulk-film counterparts. Under low pump excitation, hot-carrier cooling mediated by a phonon bottleneck is surprisingly slower in smaller nanocrystals (contrasting with conventional nanocrystals). At high pump fluence, Auger heating dominates hot-carrier cooling, which is slower in larger nanocrystals (hitherto unobserved in conventional nanocrystals). Importantly, we demonstrate efficient room temperature hot-electrons extraction (up to ∼83%) by an energy-selective electron acceptor layer within 1 ps from surface-treated perovskite NCs thin films. These insights enable fresh approaches for extremely thin absorber and concentrator-type hot-carrier solar cells.
Highlights
Hot-carrier solar cells can overcome the Shockley–Queisser limit by harvesting excess energy from hot carriers
The highenergy tails of the PB peak originate from the rapid distribution of initial non-equilibrium carriers into a Fermi-Dirac distribution via elastic scatterings that can be characterized by a carrier temperature Tc
Hot-carrier cooling in NCs is mediated by the phonon bottleneck effect, which is surprisingly slower in smaller NCs
Summary
Hot-carrier solar cells can overcome the Shockley–Queisser limit by harvesting excess energy from hot carriers. We demonstrate efficient room temperature hot-electrons extraction (up to B83%) by an energy-selective electron acceptor layer within 1 ps from surface-treated perovskite NCs thin films These insights enable fresh approaches for extremely thin absorber and concentrator-type hot-carrier solar cells. Our results revealed that the weakly confined MAPbBr3 NCs (Supplementary Fig. 4 and Supplementary Note 1) are very promising hot-carrier absorber materials as they possess much higher hot-carrier temperatures and longer cooling times (as compared with typical perovskite bulk films under comparable photoexcitation conditions). This is attributed to their intrinsic phonon bottleneck and Auger-heating effects at low and high carrier densities, respectively. The hot carriers can be efficiently extracted from MAPbBr3 NC thin films at room temperature by using a molecular semiconductor as an energy selective contact
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