Photon recycling in lead iodide perovskite 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.
Pazos-Outón, L.M, Szumilo, M, Lamboll, R, Richter, J.M, Crespo-Quesada, M, Abdi-Jalebi, M, … Deschler, F. (2016). Photon recycling in lead iodide perovskite solar cells. Science, 351(6280), 1430–1433. doi:10.1126/science.aaf1168