Electronic structure of organic-inorganic perovskites
In the quest for new, cost-effective photovolatic materials, the organic-inorganic perovskite MAPbI3 turned out to be an extremely efficient solar absorber. We analysed in detail the electronic structure of MAPbI3-derived compounds and interfaces, finding a thier relative energy level alignments, possible paths for charge transfer and transport, and strategies to tune the doping level, and hence the charge transfer possibility between different compounds.
M. Caputo,, Sci Rep 9, 15159 (2019).
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The organic-inorganic Methylammonium Lead Iodide (MAPbI3) perovskite immediately caught the attention of the scientific community in the quest for efficient and cost-effective solar energy harvester materials. It combines, in fact, the high efficiency proper of classical semiconductor-based solar cells (Si and CIGS, for instance) - up to 25% - with the low-cost materials and fabrication processes proper of the organic solar cells. To optimise the overall efficiency of a solar cell, however, solar absorbers must be combined with proper electrodes, in order to ensure an efficient separation and transport of the excited charges. Therefore, a detailed knowledge of the energetic level alignment between the organic-inorganic perovskite and its potential electrodes, and understanding how this can be tailored, is mandatory. |
In this paper we tackle exactly this problem, with an accurate joined diffraction-photoemission-computational approach to the relative band alignment among the canonical MAPbI3 perovskite, the Cl-containing perovskite (MAPbCl3), their lead halide precursors (PbI2 and PbCl2 respectively), together with a mixed MAPbI3 - MAPbCl3 perovskite phase.
Diffractograms showed immediately that the mixed phase is actually composed by crystals of the two pure MAPbI3 and MAPbCl3 perovskites. At the same time, through photoemission spectroscopy we could define precisely the frontier orbitals energy, together with their vacuum energy level. These are two fundamentals quantities to define wether the energy levels of a junction are properly aligned in order to efficiently dissociate the photo generated electron-hole pairs. In our case we found that a photo generated electron hole pair in MAPbI3 can just transfer holes in PbI2, while all the other charge transfer processes are inibite by the energy level alignment. |
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Electronic structure of MAPbI3 and MAPbCl3: importance of band alignment |
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