Efficient Bidentate Molecules Passivation Strategy for High‐Performance and Stable Inorganic CsPbI₂Br Perovskite Solar Cells

Abstract

Cesium-based all-inorganic perovskites have witnessed extraordinary advances owing to their eye-catching thermal-resistance and photoelectric properties in optoelectronics and photonics application, including solar cells, [1-5] light-emitting diodes, [6,7] photodetectors, [8,9] nanolasers application, [9,10] and so on. In particular, inducing a prominent trade-off between the light absorption and phase stability in comparison with CsPbBr 3 and CsPbI 3 perovskites, [11-13] the mixed-halide inorganic CsPbI 2 Br perovskites with the suitable bandgap have great potential in the application of burgeoning tandem solar cells and semitransparent photovoltaic devices. [14-16] Unfortunately, the serious energy losses (E loss) derived from deleterious nonradiative recombination [17,18] and inimical phase transformation to photo-non-active phase upon exposing to high humidity environment [15,19] are still the primary bottleneck hindering the further commercialization. Consequently, fabricating efficient and stable CsPbI 2 Br perovskite solar cells (PSCs) is a challenging but crucial and meaningful task. It is widely reported that the proliferated dangling bonds at the grain boundaries cause the formation of undesired point defects that result in the carrier recombination and propel the phase transformation to nonfunctional δ phase. [20-22] Moreover, the inimical pinholes caused by poor crystallization make grain boundaries the most susceptible to external erosion, such as moisture and oxygen. [23-25] Thus, considering that the detrimental nonradiative recombination and moisture-driven phase transformation preferentially occur along the weakest grain boundaries region, modulating perovskite crystallization to lower grain boundaries density and passivating defects at the grain boundaries are desirable for fabricating high-quality and stable perovskite films. [26,27] In the past few years, for achieving this target, quite a few strategies have been proposed, [28-37] among which, additive engineering has significantly encouraged the improvement of power conversion efficiency (PCE) performance and stability. [38,39] The reported additives not only gift perovskite films with enhanced crystallinity along with enlarged grain size, but also are advantageous to passivate defect states, thereby lessening the detrimental carrier recombination. Moreover, it is worthwhile mentioning that many additives play a crucial role in the stability improvement. Ma et al. found that guanidinium cations (GA þ) additives in the substitutional sites of perovskite lattice could stabilize the α phase and facilitate a high crystalline CsPbI 2 Br through the relaxation of the lattice strain and the formation of hydrogen bonds, which renders a low fabrication temperature of 140 C. Moreover, GA þ-mediated devices exhibited the superior moisture stability and decreased by only 6% of origin PCE value after 1000 h aging. [31] Wang et al. judiciously incorporated CuBr 2

All‐Inorganic CsPbI2Br Perovskite Solar Cells: Recent Developments and Challenges

“…Annihilating such defects states by introducing organic molecules embracing functional groups possessing Lewis base nature has been reported for the passivation of undercoordinated Pb 2+ ions. Li et al [ 224 ] developed a passivation strategy by introducing bidentate molecules to achieve an efficient defect passivation and crystallization modulation, thus realizing compact and pinhole‐free CsPbI 2 Br films. It was suggested that the introduction of the bidentate molecules improved the grain size of the film and effectively reduced trap density and in so doing suppressed the unfavorable carrier recombination.…”

“…[ 20,240,241 ] On the contrary, a large number of reported additives have weak interaction with Pb, resulting in a relatively labile passivation effect. Li et al [ 224 ] described a method for facial passivation that utilizes the bifunctional molecule 2‐(2 0‐thienyl)pyridine (2‐ThPy) to achieve both crystallization modulation and efficient defect passivation, resulting in high‐quality CsPbI 2 Br films. In comparison with its monodentate counterparts, 2‐methyl pyridine (2‐MPy) and 2‐methyl thiophene (2‐MTh), 2‐ThPy can strongly anchor Pb ions via S atoms in thienyl and N atoms in pyridyl, which are more conducive to delaying crystallization and accurately passivating halogen vacancies.…”

Multistrategy Toward Highly Efficient and Stable CsPbI2Br Perovskite Solar Cells Based on Dopant‐Free Poly(3‐Hexylthiophene)

“…[15,16] To address these issues, chemical composition engineering such as Rb þ , [17] Ba 2þ , [18] Eu 2þ , [19] In 3þ , [13] CH 3 COO À (Ac À ), [20] and Cl À [13] have been utilized to improve film morphology and enhance α phase stability of CsPbI 2 Br perovskite. Meanwhile, 4-aminobenzoic acid (ABA), [21] guanidinium hydrobromide (GABr), [22] 2-(2 0 -thienyl)pyridine (2-ThPy) [23] and other molecules have been introduced in precursor to passivate CsPbI 2 Br perovskite films, through the coordination of…”

Dual‐Functional Quantum Dot Seeding Growth of High‐Quality Air‐Processed CsPbI2Br Film for Carbon‐Based Perovskite Solar Cells

“…is a prerequisite for high-efficiency PSCs. Therefore, various strategies in both the film fabrication and posttreatments, such as different crystallization control methods, [31,32] doping, [33][34][35][36][37][38] additive engineering, [39,40] interface engineering, [16,30,[41][42][43] etc., have been adopted to improve the quality of CsPbI 2 Br films. Among these strategies, additive engineering with the introduction of additives into the perovskite precursor solution in the film fabrication process is a simple and effective means to modulate the crystallization and improve film quality.…”

“…Most researchers focus on organic small molecules or polymers as additives in perovskite precursors. [39,40] However, the main effect of these additives is to control the crystal growth or passivate the defect states of the perovskite film, while it has a weak effect on the nucleation process.…”