Photon recycling in lead iodide perovskite solar cells

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Reference L.M. Pazos-Outón, M. Szumilo, R. Lamboll, J.M. Richter, M. Crespo-Quesada, M. Abdi-Jalebi, H.J. Beeson, H.J. Snaith, B. Ehrler, R.H. Friend and F. Deschler, Photon recycling in lead iodide perovskite solar cells, Science 351, 6280: 1430-1433 (2016)
Group Hybrid Solar Cells

Lead-halide perovskites have emerged as high-performance photovoltaic materials. We mapped the propagation of photogenerated luminescence and charges from a local photoexcitation spot in thin films of lead tri-iodide perovskites. We observed light emission at distances of ≥50 micrometers and found that the peak of the internal photon spectrum red-shifts from 765 to ≥800 nanometers. We used a lateral-contact solar cell with selective electron- and hole-collecting contacts and observed that charge extraction for photoexcitation >50 micrometers away from the contacts arose from repeated recycling between photons and electron-hole pairs. Thus, energy transport is not limited by diffusive charge transport but can occur over long distances through multiple absorption-diffusion-emission events. This process creates high excitation densities within the perovskite layer and allows high open-circuit voltages.