Xinyi Shen1,Benjamin Gallant1,Philippe Holzhey1,Joel Smith1,Melissa McCarthy1,Karim Elmestekawy1,Yen-Hung Lin1,Zhongcheng Yuan1,Akash Dasgupta1,Laura Herz1,2,Henry Snaith1
University of Oxford1,TU Munich2
Xinyi Shen1,Benjamin Gallant1,Philippe Holzhey1,Joel Smith1,Melissa McCarthy1,Karim Elmestekawy1,Yen-Hung Lin1,Zhongcheng Yuan1,Akash Dasgupta1,Laura Herz1,2,Henry Snaith1
University of Oxford1,TU Munich2
Metal halide perovskite-based tandem solar cells combining absorbers of different bandgaps are promising to achieve light-to-electricity power conversion efficiencies (PCE) beyond the theoretical limits for their single-junction counterparts. However, significant open-circuit voltage deficits present in wide-bandgap perovskite solar cells remain major hurdles for realising efficient and stable perovskite tandem cells. The underlying mechanisms widely believed to be responsible for mediocre wide-bandgap perovskite solar cells include non-radiative interfacial losses,<sup>[1–3]</sup> halide segregation,<sup>[4]</sup> as well as heterogeneous crystallisation,<sup>[5]</sup> resulting in low open-circuit voltage (<i>V</i><sub>OC</sub>). Moreover, compared to narrow-bandgap perovskite solar cells (i.e., 1.6 eV and below), wide-bandgap perovskite solar cells exhibit more rapid perovskite degradation under accelerated ageing conditions (e.g., light, moisture, heat and oxygen),<sup>[17]</sup> mainly due to the complex composition and processing requirements of this class of perovskite, which can be a great concern for perovskite solar cells stability. Hence, effective strategies to form low-loss and stable wide-bandgap perovskites will be the key to helping the commercial deployment of perovskite tandem solar cells in the near future.<br/> <br/>In this study, we report a holistic approach to overcoming challenges in 1.8-eV perovskites by examining a series of chloride additives to engineer intermediate phases during the crystallisation process. Utilizing a carbazole-based self-assembled monolayer as the hole transport layer, synergistic improvement of the perovskite materials, and its interface with the hole transport layer allows us to achieve a maximum power point-tracked PCE (<i>η</i><sub>mpp</sub>) of 17% and a steady-state <i>V</i><sub>OC</sub> of 1.25 V. In addition, the chloride-modified perovskite material demonstrates improved ambient stability (25 °C, relative humidity = 40% in the air in dark) and suppressed halide segregation compared to no-chloride reference perovskites. In the meantime, we elucidated the role of chloride additives in controlling the intermediate phase formation and detailed subsequent materials properties of chloride-engineered wide-bandgap perovskites. Understanding such underlying mechanisms will help address one of the most challenging aspects in the commercial deployment of perovskite tandem technologies.<br/> <br/> <br/> <br/>[1] J. Wen, Y. Zhao, Z. Liu, H. Gao, R. Lin, S. Wan, C. Ji, K. Xiao, Y. Gao, Y. Tian, J. Xie, C. J. Brabec, H. Tan, <i>Adv. Mater.</i> <b>2022</b>, e2110356.<br/>[2] W. Chen, Y. Zhu, J. Xiu, G. Chen, H. Liang, S. Liu, H. Xue, E. Birgersson, J. W. Ho, X. Qin, J. Lin, R. Ma, T. Liu, Y. He, A. M.-C. Ng, X. Guo, Z. He, H. Yan, A. B. Djurišić, Y. Hou, <i>Nature Energy</i> <b>2022</b>, 1.<br/>[3] T. Huang, S. Tan, S. Nuryyeva, I. Yavuz, F. Babbe, Y. Zhao, M. Abdelsamie, M. H. Weber, R. Wang, K. N. Houk, C. M. Sutter-fella, Y. Yang, <b>2021</b>, 1.<br/>[4] M. Long, T. Zhang, M. Liu, Z. Chen, C. Wang, W. Xie, <b>n.d.</b>, DOI 10.1002/adma.201801562.<br/>[5] S. Mahesh, J. M. Ball, R. D. J. Oliver, D. P. McMeekin, P. K. Nayak, M. B. Johnston, H. J. Snaith, <i>Energy Environ. Sci.</i> <b>2020</b>, <i>13</i>, 258.