First Principles Simulations on the Role of Chlorine Doping in Organohalide Lead Perovskites
Edoardo Mosconi a, Filippo De Angelis a, Claudio Quarti a
a Computational Laboratory for Hybrid/Organic Photovoltaics, ISTM-CNR Perugia, Via Elce di Sotto 8, Perugia, 6123, Italy
International Conference on Hybrid and Organic Photovoltaics
Proceedings of 6th International Conference on Hybrid and Organic Photovoltaics (HOPV14)
Ecublens, Switzerland, 2014 May 11th - 14th
Organizers: Michael Graetzel and Mohammad Nazeeruddin
Oral, Filippo De Angelis, presentation 236
Publication date: 1st March 2014

Methylammonium lead-iodide, MAPbI3, and the mixed halide MAPbI3-xClx analogue are dominating the field of perovskite-based photovoltaics.  Despite the low Cl-doping level (~1-2%)  [1] in MAPbI3-xClx this material showed improved performances in TiO2-free devices compared to MAPbI3.[2, 3] Meso-superstructured and planar heterojunction solar cells were successfully implemented with MAPbI3-xClx, [2, 3] while the same devices based on the prototype MAPbI3 perovskite showed comparably lower performances.[4] This behavior can be interpreted on the basis of the improved carrier mobility of MAPbI3-xClx,[4] which showed electron-hole diffusion lengths exceeding 1 µm, against ~one order of magnitude smaller diffusion lengths independently measured for MAPbI3.[4, 5] Recent studies suggest that both materials show comparable carrier mobility but exhibit a markedly different recombination kinetics.[6]  

The intimate materials properties underlying the photovoltaic performance of MAPbI3-xClx and in particular the role of Cl-doping are however not yet clear. Here we investigate the effect of Cl-doping on the MAPbI3 perovskite by state of the art DFT and GW electronic structure calculations. The calculated band structures reveal similar band-gaps and carrier effective masses for MAPbI3 and for low levels of Cl-doping. Ab initio molecular dynamics simulations performed on MAPbI3 and MAPbI3-xClx suggest different structural properties for the Cl-doped material. The implications of these findings for charge generation and recombination in solar cells are discussed.

Optimized geometries of two representative structures of the 4% chloride-doped MAPbI3-xClx. Three different geometry orientations are shown. The position of the chloride ions is highlighted by yellow circles; Pb=light blue; I = magenta.
[1] Colella, S.; Mosconi, E.; Fedeli, P.; Listorti, A.; Gazza, F.; Orlandi, F.; Ferro, P.; Besagni, T.; Rizzo, A.; Calestani, G.; Gigli, G.; De Angelis, F.; Mosca, R. Chem. Mater. 2013, 25, 4613–4618. [2] Liu, M.; Johnston, M. B.; Snaith, H. J. Nature 2013, 501, 395-398. [3] Lee, M. M.; Teuscher, J.; Miyasaka, T.; Murakami, T. N.; Snaith, H. J. Science 2012, 338, 643-647. [4] Stranks, S. D.; Eperon, G. E.; Grancini, G.; Menelaou, C.; Alcocer, M.J.P.; Leijtens, T.; Herz, L.M.; Petrozza, A.; Snaith, H.J. Science, 2013, 342, 341-344. [5] Xing, G.; Mathews, N.; Sun, S.; Lim, S.S.; Lam, Y.M.; Grätzel, M.; Mhaisalkar, S.; Sum, T.C. Science, 2013, 342, 344-347. [6] Wehrenfennig , C.; Eperon , G.E.; Johnston , M.B.; Snaith , H.J.; Herz, L.M. Adv. Mater. 2013, DOI: 10.1002/adma.201305172
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