The commonly-used superstrate configuration in all-perovskite tandem solar cells is disadvantageous for long-term stability due to oxidizable narrow-bandgap perovskite assembled last and easily exposable to air. This research reverses the processing order, demonstrating all-perovskite tandems in a substrate configuration to bury the oxidizable perovskite deep within the device. Using a guanidinium tetrafluoroborate additive in the wide-bandgap perovskite subcell achieves 25.3% efficiency. Unencapsulated devices show no degradation after 1000 hours in dry air. The substrate configuration also allows for flexible substrates, achieving 24.1% and 20.3% efficiency on copper-coated polyethylene naphthalene and copper metal foil, respectively. This configuration offers a promising route to commercialization.

Yurui Wang, Renxing Lin, Xiaoyu Wang, Chenshuaiyu Liu, Yameen Ahmed, Zilong Huang, Zhibin Zhang, Hongjiang Li, Mei Zhang, Yuan Gao, Haowen Luo, Pu Wu, Han Gao, Xuntian Zheng, Manya Li, Zhou Liu, Wenchi Kong, Ludong Li, Kaihui Liu, Makhsud I. Saidaminov, Lijun Zhang, Hairen Tan