On the Impact of Different Interfaces on the Charge Carrier Transport in Perovskite Solar Cells

Polycrystalline perovskite solar cells feature a variety of interfaces on different length scales, including heterointerfaces, grain or subgranular domain boundaries. Via unsaturated bonds or structural disorder these interfaces can introduce mid-bandgap trap states, host dopants or act as to electrostatic barriers. The implications for charge carriers can be manifold: interfaces can lead to the formation of non-radiative recombination centers, delay or restrict the charge transport or, in some cases, improve the transport properties through a local change in doping concentration.
Here, we will present our investigations on the influence of subgranular ferroelastic domains and grain boundaries in MAPbI₃ on the charge carrier transport. Using a combination of advanced electromechanical atomic force microscopy (AFM) with spatial and time-resolved photoluminescence (PL) microscopy, we were able to show that the domain walls as extended structural defects delay the charge carrier diffusion by acting as electrostatic barriers.¹ However, the possibility to tailor the arrangement and density of these ferroelastic domains allows engineering a directional charge transport and improved device performance.² Moreover, using conductive AFM with PL we were able to measure single grain boundary resistances and intergranular charge carrier diffusion between neighboring single crystalline MAPbI₃ grains, illustrating a substantial impediment of the charge carrier transport across grain boundaries.
1. I. M. Hermes, A. Best, L. Winkelmann, J. Mars, S. M. Vorpahl, M. Mezger, L. Collins, H. J. Butt, D. S. Ginger, K. Koynov and S. A. L. Weber, Energy & Environmental Science, 2020, 13, 4168-4177.
2. Y. Yalcinkaya, I. M. Hermes, T. Seewald, K. Amann Winkel, L. Veith, L. Schmidt Mende and S. A. Weber, Advanced Energy Materials, 2022, 12, 2202442.