Synergistic surface modification of tin-lead perovskite solar cells
Advanced Materials Wiley 35:9 (2023) 2208320
Authors:
Shuaifeng Hu, Pei Zhao, Kyohei Nakano, Robert DJ Oliver, Jorge Pascual, Joel A Smith, Takumi Yamada, Minh Anh Truong, Richard Murdey, Nobutaka Shioya, Takeshi Hasegawa, Masahiro Ehara, Michael B Johnston, Keisuke Tajima, Yoshihiko Kanemitsu, Henry J Snaith, Atsushi Wakamiya
Abstract:
Interfaces in thin-film photovoltaics play a pivotal role in determining device efficiency and longevity. Herein, we study the top surface treatment of mixed tin-lead (∼1.26 eV) halide perovskite films for p-i-n solar cells. We are able to promote charge extraction by treating the perovskite surface with piperazine. This compound reacts with the organic cations at the perovskite surface, modifying the surface structure and tuning the interfacial energy level alignment. In addition, the combined treatment with C<sub>60</sub> pyrrolidine tris-acid (CPTA) reduces hysteresis and leads to efficiencies up to 22.7%, with open-circuit voltage values reaching 0.90 V, ∼92% of the radiative limit for the band gap of this material. The modified cells also show superior stability, with unencapsulated cells retaining 96% of their initial efficiency after >2000 hours of storage in N<sub>2</sub> and encapsulated cells retaining 90% efficiency after >450 hours of storage in air. Intriguingly, CPTA preferentially binds to Sn<sup>2+</sup> sites at film surface over Pb<sup>2+</sup> due to the energetically favoured exposure of the former, according to first-principles calculations. This work provides new insights into the surface chemistry of perovskite films in terms of their structural, electronic, and defect characteristics and we use this knowledge to fabricate state-of-the-art solar cells.
