High open-circuit voltage solar cells are important in spectral splitting systems to optimize the use of high-energy photon photons and to drive a variety of electrochemical reactions. Hybrid organic-inorganic lead halide perovskites with the generic structural formula AMX3 (where ‘A’ is a usually an organic monovalent cation, ‘M’ is the divalent metal center and ‘X’ is a halide) have been thoroughly studied in the last few years but still face stability issues. Among the possible solutions replacing the organic moiety by cesium has gained increasing attention [1], [2]. While it has been shown that high-band gap (>2 eV) devices made from CsPbBr3 as an absorber layer can work equally well as, and with better stability than devices based on CH3NH3PbBr3 [3], there are still large gaps in our knowledge regarding how the inorganic halide perovskite photovoltaic devices operate.
In this presentation we discuss what the working mechanisms of CsPbBr3-based devices are, by comparing the Cs with the organic perovskite in terms of how free carriers are separated, the width of the space charge region and the diffusion length as measured by Electron Induced Beam Current (EBIC) under different conditions in the scanning electron microscope.
EBIC uses the electron beam to act as a light source equivalent (electrovoltaic, instead of photovoltaic effect), generating electron-hole pairs in the junction area. If these pairs separate into free carriers, and are collected at the contacts, we measure a current in real time and a current collection efficiency image can be drawn.
References
[1] McMeekin, D. P.; et al., Science (2016), 351, 151–155.
[2] Kulbak, M.; Cahen, D.; Hodes, G., J. Phys. Chem. Lett. (2015), 6, 2452–2456.
[3] Kulbak, M.; Gupta, S.; Kedem, N.; Levine, I.; Bendikov, T.; Hodes, G.; Cahen, D., J. Phys. Chem. Lett. (2016), 7, 167–172.
