In Situ Tin(II) Complex Antisolvent Process Featuring Simultaneous Quasi‐Core–Shell Structure and Heterojunction for Improving Efficiency and Stability of Low‐Bandgap Perovskite Solar Cells

Abstract

Unlike Pb‐based perovskites, it is still a challenge for realizing the targets of high performance and stability in mixed Pb–Sn perovskite solar cells owing to grain boundary traps and chemical changes in the perovskites. In this work, proposed is the approach of in‐situ tin(II) inorganic complex antisolvent process for specifically tuning the perovskite nucleation and crystal growth process. Interestingly, uniquely formed is the quasi‐core–shell structure of Pb–Sn perovskite–tin(II) complex as well as heterojunction perovskite structure at the same time for achieving the targets. The core–shell structure of Pb–Sn perovskite crystals covered by a tin(II) complex at the grain boundaries effectively passivates the trap states and suppresses the nonradiative recombination, leading to longer carrier lifetime. Equally important, the perovskite heterostructure is intentionally formed at the perovskite top region for enhancing the carrier extraction. As a result, the mixed Pb–Sn low‐bandgap perovskite device achieves a high power conversion efficiency up to 19.03% with fill factor over 0.8, which is among the highest fill factor in high‐performance Pb–Sn perovskite solar cells. Remarkably, the device fail time under continuous light illumination is extended by over 18.5‐folds from 30 to 560 h, benefitting from the protection of the quasi‐core–shell structure.

High‐Performance Tin–Lead Mixed‐Perovskite Solar Cells with Vertical Compositional Gradient

“…The unencapsulated devices were stored under continuous white-light illumination (100 mW cm −2 ) in a N 2 glovebox and measured under ambient condition at specific time interval. The target devices can retain about 90% of their initial efficiency after 150 h light soaking, which are among the most stable Sn-Pb mixed PSCs reported up to now, [62][63][64] while the control without HBA remains only about 60% of their initial values under the same condition. The enhanced lightsoaking stability can be ascribed to the presence of HBA-SnF 2 complex at grain boundaries to passivate defects.…”

Inorganic top electron transport layer for high performance inverted perovskite solar cells

“…25,34,51,[194][195][196][197][198][199] Among them, PCBM was used as ETL in most p-i-n PSC cases. [7][8][9][10]200,201 However, there are some shortcoming for fullerene different electron transport materials (ETMs), such as narrow range of LUMO level, relatively poor morphological stability, and high cost of synthesis and purification. 199 As shown above, some intrinsic weak points exactly exist in organic top ETL.…”

“…Known to be a star ETL, fullerene and it derivative such as [6,6]phenyl-C61-butyric acid methyl ester (PCBM) has been widely used in inverted PSCs, exhibiting negligible hysteresis. [6][7][8][9][10] However, difference between the Fermi level of PCBM and the work function of Ag electrode often results in Schottky barrier at their interface, 11 leading to charge carrier recombination and high series resistance (R S ) and thus low PSC performance. To address these issues, inorganic top ETLs have been used due to their advantages such as good optical and electrical properties, low cost, facile synthesis, controllable properties, and so forth.…”

Interface Engineering of Pb–Sn Low‐Bandgap Perovskite Solar Cells for Improved Efficiency and Stability

“…Nevertheless, the V oc obtained with this strategy was still lower compared with that of the commonly used PEDOT: PSS. [12,20,[32][33][34][44][45][46] Yang et al used PEDOT:PSS and PTAA bilayer as HTL to fabricate LBG PSCs but no detailed study highlighting the effect of the bilayer is reported. [47] The focus of the work was to enhance the charge carrier diffusion length of the LBG perovskite using a trace amount of cadmium ions into the perovskite precursor, where a PCE of 20.3% was demonstrated.…”

“…Several efforts have been devoted to improve the interfaces and film quality of the Pb–Sn‐mixed LBG PSCs. [ 14–39 ] In particular, Xu and co‐workers used the ultrathin bulk‐heterojunction organic semiconductor (PBDB‐T:ITIC) layer as an intermediary between the hole‐selective layer (HSL) and Pb–Sn‐based perovskite layer to form a cascaded hole transport interface and minimize carrier recombination at the interface. As a result, the PCE of 18.03% with a remarkably high V OC up to 0.86 V was obtained.…”