Light-Induced Increase of Electron Diffusion Length
in a p–n Junction Type CH<sub>3</sub>NH<sub>3</sub>PbBr<sub>3</sub> Perovskite Solar Cell
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Abstract
High band gap, high open-circuit
voltage solar cells with methylammonium
lead tribromide (MAPbBr<sub>3</sub>) 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-beam-induced
current (EBIC) measurements, we find an increase in carrier diffusion
length in MAPbBr<sub>3</sub>(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 <i>L</i><sub>n</sub> = 100 ± 50 nm to 360 ± 22 nm. The EBIC cross section profile
indicates a p–n structure between the n-FTO/TiO<sub>2</sub> 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 MAPbBr<sub>3</sub>(Cl) to be 3–6 × 10<sup>17</sup> cm<sup>–3</sup>