Recombination Kinetics and Slow Transient Behaviour in Organic-Inorganic Perovskites

Samuel Stranks^a^,^b, Tomas Leijtens^b, Henry Snaith^b, Alain Goriely^c, Victor Burlakov^c

^aResearch Laboratory of Electronics, Massachusetts Institute of Technology - USA, Massachusetts Avenue, 77, Cambridge, United States

^bDepartment of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom

^cMathematical Institute, University of Oxford, OCCAM, Woodstock Road, Oxford, OX2 6GG

International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics 2015 (HOPV15)

Roma, Italy, 2015 May 11th - 13th

Organizer: Filippo De Angelis

Oral, Samuel Stranks, presentation 256
Publication date: 5th February 2015

Organic-inorganic perovskites have attracted an enormous amount of recent attention and have the potential to be a “disruptive” photovoltaic technology, with certified power conversion efficiencies already exceeding 20%. Nevertheless, a detailed understanding of recombination pathways and an explanation for the observed slow transient behaviour, crucial for further device improvement, are still required. We have recently developed a very generic yet analytically solvable model describing the recombination kinetics of photo-excited carriers in the presence of electronic sub-gap trap states in solution-processed CH₃NH₃PbI_3-xCl_x perovskite films [1]. We can use this model to estimate the sub-gap trap density, and we show that it can be more generally applied to compare the trap densities in perovskites fabricated using a variety of methods. We then speculate that the traps result from halide vacancies, and extend the model to include an interplay between the vacancies and halides in the interstitial sites. The numerical solutions are able to reproduce a wide range of experimental data, in particular providing an explanation for the very slow rise times (seconds to minutes) observed from photoluminescence and open-circuit voltage measurements following illumination. We show how the work relates to the effects reported in recent passivation [2] and hysteresis [3] studies. Our work provides an understanding of how to further enhance the material performance for high-efficiency perovskite solar cells and light-emitting devices.

[1] Stranks, S. D.; Burlakov, V. M.; Leijtens, T.; Ball, J. M.; Goriely, A.; Snaith, H. J. Recombination Kinetics in Organic-Inorganic Perovskites: Excitons, Free Charge, and Subgap States. Physical Review Applied 2014, 2. [2] Noel, N. K.; Abate, A.; Stranks, S. D.; Parrott, E. S.; Burlakov, V. M.; Goriely, A.; Snaith, H. J. ACS Nano 2014, 8, 9815-9821. [3] Unger, E. L.; Hoke, E. T.; Bailie, C. D.; Nguyen, W. H.; Bowring, A. R.; Heumuller, T.; Christoforo, M. G.; McGehee, M. D. Energy & Environmental Science 2014, 7, 3690-3698.

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