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Electronic structure of MAPbI3 and MAPbCl3: importance of band alignment 

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.

Finally, our mixed MAPbI3 - MAPbCl3 perovskite phase showed that is possible to tune the energy level alignment through a proper choice of the substrate used to grow the samples.


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Electronic structure of MAPbI3 and MAPbCl3: importance of band alignment 


Marco Caputo1*, Nicola Cefarin2,3, Andrea Radivo1,2, Nicola Demitri1, Lara Gigli1, Jasper R. Plaisier1, Mirco Panighel1,3, Giovanni Di Santo1, Sacha Moretti4, Angelo Giglia2, Maurizio Polentarutti1, Filippo De Angelis5,6, Edoardo Mosconi5,6, Paolo Umari2,7, Massimo Tormen2 & Andrea Goldoni1*
*Corresponding authors
1 Sincrotrone Trieste SCpA, I-34149 Trieste, Italy
2 Istituto Officina dei Materiali - CNR, Laboratorio TASC, I-34149 Trieste, Italy
3 University of Trieste, Piazzale Europa, I-34127 Trieste, Italia
4 Istituto di ricerca sull'inquinamento atmosferico - CNR, I-87036 Rende, Italy
5 Laboratorio computazionale per fotovoltaico ibrido/organico  - CNR, I-06123 Perugia, Italy
6 CompuNet - IIT, I-16163 Genova, Italy
7University of Padua, I-35131 Padua, Italy

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Sci Rep 9, 15159 (2019)
DOI: 0.1038/s41598-019-50108-0
Received 17 June 2019, Accepted 28 August 2019

First published online 22 October 2019

Last Updated on Friday, 08 January 2021 11:06