Multimodal Operando Microscopy Reveals that Nanoscale Performance Disorder Dictates Efficiency and Stability of Perovskite Solar Cells

The optoelectronic properties of next generation semiconductors such as halide perovskites are dominated by nanoscale variations in structure^1,2, composition^3,4 and photophysics^5,6. While microscopy provides a proxy for ultimate device function, past works have typically focused on neat films fabricated on insulating substrates – therefore missing additional recombination losses from transport layers and charge extraction losses entirely^7–9.<br/>In this presentation, I will discuss a multimodal, <i>operando</i>, microscopy toolkit designed to measure nanoscale current-voltage curves, recombination losses and chemical composition in a wide array of state-of-the-art perovskite solar cells before and after extended operational stress. By imaging the same scan areas before and after operation, we determine point by point changes in recombination and transport losses on length scales from entire device down to sub-micron.<br/>We apply this toolkit to reveal that perovskite solar cells with the highest performance and stability have the lowest initial performance spatial heterogeneity. We show that perovskite solar cells can tolerate considerable chemical and photophysical heterogeneity in the absorber itself, but cannot tolerate heterogeneous charge extraction, a finding missed by conventional microscopy. If the interfaces are not stabilised appropriately, the contacts dominate degradation pathways, introducing spatially varying transport, recombination, and hysteresis losses. With well-tuned contact layers, perovskite absorbers dominate degradation and minor modulations of the composition can induce or prevent extreme halide segregation and precipitate formation which are both detrimental to performance. These <i>operando</i> measurements uniquely unveil the underpinnings of perovskite solar cell performance and stability. The microscopy toolbox can be readily tuned for alternative device structures and semiconductors.<br/><b>References</b><br/>1. Doherty, T. A. S. <i>et al.</i> Performance-limiting nanoscale trap clusters at grain junctions in halide perovskites. <i>Nature</i> vol. 580 360–366 (2020).<br/>2. Doherty, T. A. S. <i>et al.</i> Stabilized tilted-octahedra halide perovskites inhibit local formation of performance-limiting phases. <i>Science</i> vol. 374 1598–1605 (2021).<br/>3. Frohna, K. <i>et al.</i> Nanoscale chemical heterogeneity dominates the optoelectronic response of alloyed perovskite solar cells. <i>Nature Nanotechnology</i> vol. 17 190–196 (2022).<br/>4. Correa-Baena, J.-P. <i>et al.</i> Homogenized halides and alkali cation segregation in alloyed organic-inorganic perovskites. <i>Science</i> vol. 363 627–631 (2019).<br/>5. de Quilettes, D. W. <i>et al.</i> Impact of microstructure on local carrier lifetime in perovskite solar cells. <i>Science</i> vol. 348 683–686 (2015).<br/>6. Macpherson, S. <i>et al.</i> Local nanoscale phase impurities are degradation sites in halide perovskites. <i>Nature</i> vol. 607 294–300 (2022).<br/>7. Stolterfoht, M. <i>et al.</i> Visualization and suppression of interfacial recombination for high-efficiency large-area pin perovskite solar cells. <i>Nature Energy</i> vol. 3 847–854 (2018).<br/>8. Stolterfoht, M. <i>et al.</i> The impact of energy alignment and interfacial recombination on the internal and external open-circuit voltage of perovskite solar cells. <i>Energy & Environmental Science</i> vol. 12 2778–2788 (2019).<br/>9. Cacovich, S. <i>et al.</i> Imaging and quantifying non-radiative losses at 23% efficient inverted perovskite solar cells interfaces. <i>Nat. Commun.</i> <b>13</b>, 2868 (2022).