Slow cooling and highly efficient extraction of hot carriers in colloidal perovskite nanocrystals

• Published in: Nature communications Vol. 8; no. 1; p. 14350
• Main Authors: Li, Mingjie, Bhaumik, Saikat, Goh, Teck Wee, Kumar, Muduli Subas, Yantara, Natalia, Grätzel, Michael, Mhaisalkar, Subodh, Mathews, Nripan, Sum, Tze Chien
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 08-02-2017; Nature Publishing Group; Nature Portfolio
• Subjects: 140/125; 140/146; 639/301/299/946; 639/925/357/404; Humanities and Social Sciences; multidisciplinary; Nanocrystals; Science; Science (multidisciplinary)
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/ncomms14350

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.
Harvesting excess energy from above-band gap photons could lead to solar cells which exceed conventional efficiency limits. Li
et al
., study hot carrier cooling in hybrid perovskite materials with reduced dimensionality using transient absorption spectroscopy and demonstrate efficient hot-electron extraction in such systems.