Efficient green light-emitting diodes based on quasi-two-dimensional composition and phase engineered perovskite with surface passivation

The remarkable performance of hybrid perovskite photovoltaics is attributed to their long carrier lifetimes and high photoluminescence (PL) efficiencies. High-quality films are associated with slower PL decays, and it has been claimed that grain boundaries have a negligible impact on performance. We used confocal fluorescence microscopy correlated with scanning electron microscopy to spatially resolve the PL decay dynamics from films of nonstoichiometric organic-inorganic perovskites, CH3NH3PbI3(Cl). The PL intensities and lifetimes varied between different grains in the same film, even for films that exhibited long bulk lifetimes. The grain boundaries were dimmer and exhibited faster nonradiative decay. Energy-dispersive x-ray spectroscopy showed a positive correlation between chlorine concentration and regions of brighter PL, whereas PL imaging revealed that chemical treatment with pyridine could activate previously dark grains. Copyright © 2015, American Association for the Advancement of Science.

Organic-inorganic metal halide perovskites have recently emerged as a top contender to be used as an absorber material in highly efficient, low-cost photovoltaic devices. Solution-processed semiconductors tend to have a high density of defect states and exhibit a large degree of electronic disorder. Perovskites appear to go against this trend, and despite relatively little knowledge of the impact of electronic defects, certified solar-to-electrical power conversion efficiencies of up to 17.9% have been achieved. Here, through treatment of the crystal surfaces with the Lewis bases thiophene and pyridine, we demonstrate significantly reduced nonradiative electron-hole recombination within the CH(3)NH(3)PbI(3-x)Cl(x) perovskite, achieving photoluminescence lifetimes which are enhanced by nearly an order of magnitude, up to 2 μs. We propose that this is due to the electronic passivation of under-coordinated Pb atoms within the crystal. Through this method of Lewis base passivation, we achieve power conversion efficiencies for solution-processed planar heterojunction solar cells enhanced from 13% for the untreated solar cells to 15.3% and 16.5% for the thiophene and pyridine-treated solar cells, respectively.