09-Nov-2022: Talk by Sapir Bitton

On the 9th of November, Sapir Bitton a PhD student in the Organic Materials and Devices Lab at the Technion Israel Institute of Technology will give a talk entitled:

Iodine Reactions as Mobile Recombination Centers – a Drift-Diffusion Reaction Simulation of Perovskite Cells’ Degradation


Perovskite-based solar cell efficiency has risen in less than a decade from 10% to over 25%. But at the same time, these devices are unstable. Studies have shown the negative effect of humidity, oxygen, light, and heat on perovskite-based devices. Previously, we used drift-diffusion device simulation to highlight the role of ions’ penetration into the transport layers towards the contacts1-2. Here, we expand the model to include chemical reactions either within the layers or at the contacts. We show how using drift-diffusion-reaction device model one can account for the efficiency degradation of perovskite solar cells.
Ion generation of MA+ or I in MAPbI3 have low activation barriers (0.55-0.84eV and 0.33-0.58eV, respectively3) and non-negligible ionic diffusion coefficients to move within perovskite devices. 
We performed simulations of MAPbI3 perovskite solar cell containing free iodine anions (iodides). We allowed the iodides to drift and diffuse across the device4, and react as the following:
I+h→I ,  I+eVB→I,  I+eCB →I,  2I↔I2,   I2+2e→2I

This talk presents the simulations results and describes how the iodide spices inside the perovskite solar cells affect their performance.
In particular, the presentation shows the change of the perovskite layer from intrinsic to n-type, dipoles formation between the perovskite layer and the blocking layers and their effect on the device efficiency. And the most interesting part, we will discuss the degradation of the solar cell efficiency associated with the reactions of the mobile iodine elements which become also mobile recombination centers5. The relatively low diffusion coefficient implies that the reactions are diffusion limited and hence could be very slow. These slow processes may be among the reasons for the long-term efficiency degradation of perovskite solar cells.
[1] S.Bitton and N.Tessler. J. Mater. Chem. C ,9, 1888-1894 (2021)
[2] S.Bitton and N.Tessler. Appl. Phys. Lett. 117, 133904 (2020)
[3] C.Eames, J.M.Frost, P.R.F.Barnes, B.C.O’regan, A.Walsh, M.S.Islam. Nat. Commun. 2015, 6, 7497.
[4] A.Guerrero, J.You, C.Aranda, Y.S.Kang, G.Garcia-Belmonte, H.Zhou, J.Bisquert, and Y.Yang. ACS Nano 2016 10, 218-224
[5] X. Zheng, X. Wang, W. Li, Z. Liu, W. Ming, H. Wang, H. Wang, D. Li, B. Liu, and C. Yang. The Journal of Physical Chemistry C 2021 125 (35), 19551-19559

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