Datta Kunal, van Gorkom Bas T, Chen Zehua, Dyson Matthew J, van der Pol Tom P A, Meskers Stefan C J, Tao Shuxia, Bobbert Peter A, Wienk Martijn M, Janssen René A J
Molecular Materials and Nanosystems & Institute for Complex Molecular Systems, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands.
Materials Simulation and Modelling, Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands.
ACS Appl Energy Mater. 2021 Jul 26;4(7):6650-6658. doi: 10.1021/acsaem.1c00707. Epub 2021 Jul 14.
Light-induced halide segregation hampers obtaining stable wide-band-gap solar cells based on mixed iodide-bromide perovskites. So far, the effect of prolonged illumination on the performance of mixed-halide perovskite solar cells has not been studied in detail. It is often assumed that halide segregation leads to a loss of open-circuit voltage. By simultaneously recording changes in photoluminescence and solar cell performance under prolonged illumination, we demonstrate that cells instead deteriorate by a loss of short-circuit current density and that the open-circuit voltage is less affected. The concurrent red shift, increased lifetime, and higher quantum yield of photoluminescence point to the formation of relatively emissive iodide-rich domains under illumination. Kinetic Monte Carlo simulations provide an atomistic insight into their formation via exchange of bromide and iodide, mediated by halide vacancies. Localization of photogenerated charge carriers in low-energy iodide-rich domains and subsequent recombination cause reduced photocurrent and red-shifted photoluminescence. The loss in photovoltaic performance is diminished by partially replacing organic cations by cesium ions. Ultrasensitive photocurrent spectroscopy shows that cesium ions result in a lower density of sub-band-gap defects and suppress defect growth under illumination. These defects are expected to play a role in the development and recovery of light-induced compositional changes.
光致卤化物偏析阻碍了基于碘化溴混合钙钛矿获得稳定的宽带隙太阳能电池。到目前为止，长时间光照对混合卤化物钙钛矿太阳能电池性能的影响尚未得到详细研究。人们通常认为卤化物偏析会导致开路电压损失。通过同时记录长时间光照下光致发光和太阳能电池性能的变化，我们证明电池性能下降的原因是短路电流密度的损失，而开路电压受影响较小。光致发光同时出现的红移、寿命增加和量子产率提高表明，光照下形成了相对发光的富碘区域。动力学蒙特卡罗模拟通过卤化物空位介导的溴化物和碘化物交换，对其形成过程提供了原子尺度的见解。光生载流子在低能富碘区域的局域化及随后的复合导致光电流降低和光致发光红移。用铯离子部分取代有机阳离子可减少光伏性能的损失。超灵敏光电流光谱表明，铯离子会降低亚带隙缺陷的密度，并抑制光照下缺陷的生长。预计这些缺陷会在光致成分变化的发展和恢复过程中发挥作用。
