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  Kedem, N.; Brenner, T.M.; Kulbak, M.; Schaefer, N.; Levcenko, S.; Levine, I.; Abou-Ras, D.; Hodes, G.; Cahen, D.: Light-Induced Increase of Electron Diffusion Length in a p-n Junction Type CH₃NH₃PbBr₃ Perovskite Solar Cell. The Journal of Physical Chemistry Letters 6 (2015), p. 2469-2476

10.1021/acs.jpclett.5b00889
Open Access Version

Abstract:
High band gap, high open-circuit voltage solar cells with methylammonium lead tribromide (MAPbBr3) perovskite absorbers are of interest for spectral splitting and photoelectrochemical applications, because of their good performance and ease of processing. The physical origin of high performance in these and similar perovskite-based devices remains only partially understood. Using cross-sectional electron-beaminduced current (EBIC) measurements, we find an increase in carrier diffusion length in MAPbBr3(Cl)-based solar cells upon low intensity (a few percent of 1 sun intensity) blue laser illumination. Comparing dark and illuminated conditions, the minority carrier (electron) diffusion length increases about 3.5 times from Ln = 100 ± 50 nm to 360 ± 22 nm. The EBIC cross section profile indicates a p−n structure between the n-FTO/TiO2 and p-perovskite, rather than the p−i−n structure, reported for the iodide derivative. On the basis of the variation in space-charge region width with varying bias, measured by EBIC and capacitance−voltage measurements, we estimate the net-doping concentration in MAPbBr3(Cl) to be 3−6 × 1017 cm−3.