Organohalide-perovskite solar cells have emerged as a leading next-generation photovoltaic technology. However, despite surging efficiencies, many questions remain unanswered regarding the mechanisms of operation. Here we report a detailed study of the electro-optics of efficient CH 3 NH 3 PbI 3 -perovskite-only planar devices. We report the dielectric constants over a large frequency range. Importantly, we found the real part of the static dielectric constant to be ∼70, from which we estimate the exciton-binding energy to be of order 2 meV, which strongly indicates a non-excitonic mechanism. Also, Jonscher's Law behaviour was consistent with the perovskite having ionic character. Accurate knowledge of the cell's optical constants allowed improved modelling and design, and using this information we fabricated an optimized device with an efficiency of 16.5%. The optimized devices have ∼100% spectrally flat internal quantum efficiencies and minimal bimolecular recombination. These findings establish systematic design rules to achieve silicon-like efficiencies in simple perovskite solar cells.

An optical-frequency dielectric constant of 4.6 leads to improved charge generation efficiency in an organic semiconductor homojunction photovoltaic device.

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The effect of varying the emitter concentration on the structural properties of an archetypal phosphorescent blend consisting of 4,4'-bis(N-carbazolyl)biphenyl and tris(2-phenylpyridyl)iridium(III) has been investigated using nonequilibrium molecular dynamics (MD) simulations that mimic the process of vacuum deposition. By comparison with reflectometry measurements,w es howt hat the simulations provideanaccurate model of the average density of such films. The emitter molecules were found not to be evenly distributed throughout film, but rather they can form networks that providec harge and/or energy migration pathways, even at emitter concentrations as lowas% 5weight percent. At slightly higher concentrations,percolated networks form that span the entire system. While such networks would give improved charge transport, they could also lead to more non-radiative pathwaysf or the emissive state and ar esultant loss of efficiency.