Visualizing Voltage Losses in Highly Efficient and Stable Perovskite-based Tandem Solar Cells

To achieve higher electricity generation at low cost, the most substantial impact on the energy generation from solar cells is to make existing technologies more efficient per area. This forms the focus of tandem solar cells, which utilize different photoactive materials with different bandgaps, allowing to benefit from a broader range of the solar spectrum. To make efficient and stable perovskite-based multi-junction (e.g. perovskite/silicon and perovskite/perovskite tandem) solar cells – also single-junction ones –, it is important to understand the losses under device operational conditions.¹ To do so, we used absolute (photo- and electro-) luminescence imaging techniques with high spatial resolution.<br/>On the device level, recombination losses could occur either in the bulk of the perovskite or at the adjacent transport layer interfaces. Here, we visualized the interfacial recombination losses using hyperspectral imaging system by analyzing the data with home-built MatLab code. We investigated how the different passivation routes affect the quasi Fermi level splitting (QFLS) of the samples together with device performance, also the stability under different external stressors. In the case of single junction perovskite devices, the focus was on 2D perovskite layers at the electron-selective interface that passivate the trap states and suppress the ion migration. Also, the alternative passivation routes for wide bandgap perovskites such as ammonium-based passivation molecules were studied. These molecules regulate this interface that results in absolute 90 meV enhancement in QFLS. Finally, we further investigated the p-i-n perovskite/silicon monolithic tandem solar cells. Reducing the trap states at perovskite/C₆₀ interface both for single-junction and tandem solar cells not only enhances the device performance but also the stability of the devices after damp-heat testing (85°C at 85% relative humidity).^{2, 3} Further, origin of the perovskite top cell degradation in perovskite/silicon tandem devices after field test experiments was demonstrated via PL imaging.⁴<br/><br/><br/>References<br/><br/>1. Ugur, E.; Alarousu, E.; Khan, J. I.; Vlk, A.; Aydin, E.; De Bastiani, M.; Balawi, A. H.; Gonzalez Lopez, S. P.; Ledinský, M.; De Wolf, S.; Laquai, F., How Humidity and Light Exposure Change the Photophysics of Metal Halide Perovskite Solar Cells. <i>Solar RRL </i><b>2020,</b> <i>4</i>, 2000382.<br/>2. Liu, J.; De Bastiani, M.; Aydin, E.; Harrison, G. T.; Gao, Y.; Pradhan, R. R.; Eswaran, M. K.; Mandal, M.; Yan, W.; Seitkhan, A.; Babics, M.; Subbiah, A. S.; Ugur, E.; Xu, F.; Xu, L.; Wang, M.; Rehman, A. u.; Razzaq, A.; Kang, J.; Azmi, R.; Said, A. A.; Isikgor, F. H.; Allen, T. G.; Andrienko, D.; Schwingenschlögl, U.; Laquai, F.; De Wolf, S., Efficient and stable perovskite-silicon tandem solar cells through contact displacement by MgF_x. <i>Science </i><b>2022,</b> <i>377</i>, 302-306.<br/>3. Azmi, R.; Ugur, E.; Seitkhan, A.; Aljamaan, F.; Subbiah, A. S.; Liu, J.; Harrison, G. T.; Nugraha, M. I.; Eswaran, M. K.; Babics, M.; Chen, Y.; Xu, F.; Allen, T. G.; Rehman, A. u.; Wang, C.-L.; Anthopoulos, T. D.; Schwingenschlögl, U.; Bastiani, M. D.; Aydin, E.; Wolf, S. D., Damp heat-stable perovskite solar cells with tailored-dimensionality 2D/3D heterojunctions. <i>Science </i><b>2022,</b> <i>376</i>, 73-77.<br/>4. De Bastiani, M.; Van Kerschaver, E.; Jeangros, Q.; Ur Rehman, A.; Aydin, E.; Isikgor, F. H.; Mirabelli, A. J.; Babics, M.; Liu, J.; Zhumagali, S.; Ugur, E.; Harrison, G. T.; Allen, T. G.; Chen, B.; Hou, Y.; Shikin, S.; Sargent, E. H.; Ballif, C.; Salvador, M.; De Wolf, S., Toward Stable Monolithic Perovskite/Silicon Tandem Photovoltaics: A Six-Month Outdoor Performance Study in a Hot and Humid Climate. <i>ACS Energy Letters </i><b>2021,</b> <i>6</i>, 2944-2951.