The perovskite fever & unusual carrier physics

Xiaoyang Zhu, Columbia University

The remarkable discoveries of highly efficient solar cells from lead halide perovskites have led to feverish research activities on this class of hybrid organic-inorganic semiconductors. In this lecture, we will discuss unique physical properties of these materials that give rise to their exceptional solar cell performance. We focus on the polaronic nature of charge carriers that are likely reasons for the exceptionally long carrier lifetimes, exceptionally low recombination or trapping probability, and efficient suppression of electron-phonon scattering. The latter results in energetic electrons with excess energy <E*> ~ 0.25 eV above the conduction band minimum and lifetime as long as 100 ps, which is more than three-orders of magnitude longer than that in conventional semiconductors. The persistence of high-energy electrons permits their harvesting and may lead to the realization of solar cells with efficiency exceeding the Shockley-Queisser limit. The same physical properties responsible for highly efficient solar cells are also ideal for the reverse process of light emission. We show room temperature lasing from single crystal lead halide perovskite nanowires with the lowest lasing thresholds and highest quality factors reported to date for semiconductor nanowire lasers. Kinetic analysis based on time-resolved fluorescence reveals little charge carrier trapping in these single crystal nanowires and gives estimated lasing quantum yields approaching 100%, which represents orders of magnitude improvements over other nanowire lasers from conventional semiconductors.