Aggregation-induced Emission Materials for High-efficiency Perovskite Solar Cells.

The perovskite solar cells (PSCs) with high efficiency and stability are in great demand for commercial applications. Although the remarkable photovoltaic feature of perovskite layer plays a great role in improving the PCE of PSCs, the inevitable defects and poor stability of perovskite, etc. are the bottleneck and restrict the commercialization of PSCs. Herein, a review provides a strategy of applying aggregation-induced emission (AIE) molecules, containing passivation functional groups and distinct AIE character, which serves as the alternative materials for fabricating high-efficiency and high-stability PSCs. The methods of introducing AIE molecules to PSCs are also summarized, including additive engineering, interfacial engineering, hole transport materials and so on. In addition, the functions of AIE molecule are discussed, such as defects passivation, morphology modulation, well-matched energy level, enhanced stability, hole transport ability, carrier recombination suppression. Finally, the detailed functions of AIE molecules are offered and further research trend for high performance PSCs based on AIE materials is proposed.

Hydrazone dye passivator for high-performance and stable perovskite solar cells.

There has been rapid development of organic-inorganic perovskite solar cells (PSCs) in recent years, but efficiency and stability challenges remain due to the massive defects in perovskite films. Here, the organic dye Th-azi-Pyr (ethyl 2-(2-(3-methyl-5-oxo-1-phenyl-1,5-dihydro-4H-pyrazol-4-ylidene) hydrazineyl)-4,5,6,7-tetrahydrobenzo[b]thiophene-3-carboxylate) with carbonyl, pyrazolone structure, and benzene ring was synthesized and used to prepare high-quality perovskite film as an additive. Th-azi-Pyr formed relatively stable intermediate ligands with uncoordinated Pb and I, slowing the crystal growth and reducing the grain boundary defects of perovskite. In addition, the benzene ring in the dye protected against moisture and increased the stability of the perovskite film. Therefore, the Th-azi-Pyr-modified PSC assembled in an air environment exhibited a promising power conversion efficiency (PCE) of 19.27%, which is superior to the 15.33% of the control PSC. Additionally, 88% of the original performance was maintained after 300 h at 25 ± 5 °C and 50 ± 10% relative humidity, implying that the modified PSCs exhibited greater stability than the untreated PSCs. This work indicates that simple and low-cost organic dyes are excellent defect passivators for high-performance PSCs.

When Aggregation-Induced Emission Meets Perovskites: Efficient Defect-Passivation and Charge-Transfer for Ambient Fabrication of Perovskite Solar Cells.

The intrinsic defects in perovskite film can serve as non-radiative recombination center to limit the performance and stability of metal halide perovskite solar cells (PSCs). The additive engineering in perovskite film is always applied to produce high-efficiency PSCs in recent years. Here, a typical donor-acceptor (D-A) structured aggregation-induced emission (AIE) molecule tetraphenylethene-2-dicyano-methylene-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran (TPE-TCF) was introduced into perovskite film. The D-A structure of TPE-TCF molecule provided additional charge transfer channels, contributing to transporting electron of TPE-TCF-based device. The cyano (C≡N) of TPE-TCF can interact with the uncoordinated Pb to from a relatively stable intermediate, PbI2 ⋅TPE-TCF, resulting in the slower crystal growth, reduced the defects at the grain boundaries and suppressed carrier recombination. As a consequence, the power conversion efficiency (PCE) of TPE-TCF-modified PSCs achieved a remarkably enhanced from 15.63 to 19.66 % with negligible hysteresis, which was prominent in methylammonium lead iodide-based devices fabricated under ambient condition. Furthermore, the PSCs modified by AIE molecule possessed an outstanding stability and maintain about 86 % of the initial PCE after 300 h storage in air at 25-35 °C with a high relative humidity (RH) of ≈85 %. This work suggests that incorporating AIE molecule into perovskite is a promising strategy for facilitating high-performance PSCs commercialization in ambient environment without glovebox.

The disappearing additive: introducing volatile ethyl acetate into a perovskite precursor for fabricating high efficiency stable devices in open air.

In recent years, organic-inorganic halide perovskite solar cells (PSCs) have attracted massive attention because of their high power conversion efficiency (PCE). However, it is difficult to prepare perovskite films with good performance in open air due to the poor stability of perovskite materials in high humidity, which is seriously hindering the practical application and development of PSCs. Herein, ethyl acetate (EA) is introduced into the perovskite precursor to enhance the crystallinity of perovskite for fabricating high efficiency stable devices in the atmospheric environment. Interestingly, volatile EA, which is often used as an anti-solvent, could quickly evaporate and accelerate the nuclei formation during perovskite crystallization. More impressively, the Lewis base nature of EA can form strong chemical bonding interactions with perovskite to passivate the defects during crystallization. As a result, the EA-modified perovskite film demonstrates dense and defect-less morphology with large grain size (the maximum achieves 0.9 µm). The EA-treated device has a dramatic efficiency of 19.53% and negligible hysteresis of the photocurrent. Furthermore, both the temperature and humidity resistances of EA-modified PSC are significantly improved. The normalized PCE of the EA-modified device without encapsulation can still retain over 80% of its initial value after being stored in 60% relative humidity (RH) in the dark for 500 hours. This contribution provides a promising channel for facilitating the commercialization of PSCs.