Using Photocurrent imaging technique to study the stability mechanism of perovskite solar cell in humid air
Organic-inorganic perovskite (PVSK) solar cells have shown tremendous improvement in the past few years and are comparable to the best commercial solar cell technologies. The instabilities in the materials and devices are due to reactions with water. To date, PVSK solar cell degradation only has been investigated by monitoring the current-voltage (J-V) curves as a function of time under controlled temperature and humidity conditions. However, this method provides very few information about the mechanisms and processes of degradation on a microscopic level. Z. Song et al. use photocurrent imaging technique, laser beam induced current (LBIC), to investigate the spatial and temporal evolution of the quantum efficiency of PVSK solar cells under controlled humidity conditions. A four-stage process in the degradation is discovered. By utilizing LBIC imaging, it reveals a microscopic level understanding of the degradation mechanisms of PVSK solar cells, which gives instructive insight for designing strategies to improve the stability of PVSK solar cells.
▲Figure 1. LBIC EQE image (@ 532 nm) of a typical PVSK solar cell under 50±5% RH exposure.
▲Figure 2. Areal average LBIC EQE (at 532 nm) as a function of time after exposure to humidity.
▲Figure 3. LBIC EQE images for Stage 4.
▲Figure 4. Contour plots under (a) 50% RH and (b) 80% RH during Stage 3. The plots can resolve the speed of propagation of the degradation front and the degradation rate can be derived to 0.36 um s-1 and 1.48 um s-1 under 50% and 80% RH, respectively.
▲Figure 5. (a) LBIC EQE images of a hydrated PVSK device while purging with dry air. (b) Areal average EQE (at 532nm) which reveals the hydration-dehydration cycles.
▲Figure 6. Schematic diagram of the phase equilibria in PbI2-Ch3NH3I-H2O system.
Z. Song, A. Abate, S. C. Watthage, G. K. Liyanage, A. B. Phillips, U. Steiner, M. Graetzel, M. J. Heben Perovskite Solar Cell Stability in Humid Air: Partially Reversible Phase Transitions in the PbI2-CH3NH3I-H2O System. Advanced Energy Materials 2016, 1600846