Halide perovskites are considered to be next-generation semiconductor materials with bright prospects to advance the technology of photonics and optoelectronics. Because of the intrinsic ionic feature, the interactions between perovskites and water induce serious stability issues, which has been one of the fundamental problems hindering the practical application of perovskites. The degradation of halide perovskites upon water exposure has been intensively studied, resulting in chemical insights into key processes, including hydration, phase transformation, decomposition, and dissolution. In this Perspective, we try to illustrate what happens when halide perovskites meet with water. We summarize the research progress regarding the understanding of these processes and discuss the principle of strategy design toward improved stability against water. In addition to the instability-related interactions, we also discuss the aqueous solution of perovskite precursors for fabricating perovskite-based functional materials. Hopefully, this Perspective can inspire more fundamental studies on the interactions between perovskites and water, such as spectroscopy and simulation, crystal structure and material characterizations, and solution chemistry and crystallization.

What Happens When Halide Perovskites Meet with Water?

Reducing the interfacial voltage loss in tin halides perovskite solar cells

The machine learning techniques are capable of predicting virtual material design space and optimizing material fabrication parameters. In this article, we construct machine learning models to describe the photoelectrochemical properties of molecularly engineered halide perovskite materials based on CH3NH3PbI3 in an aqueous solution and predict a complex multidimensional design space for the halide perovskite materials. The machine learning models are trained and tested based on an experimental photocurrent data set consisting of 360 data points with varying experimental conditions and dye structures. Machine learning algorithms including support vector machine (SVM), random forest, k-nearest neighbors, Rpart, Xgboost, and Kriging algorithms are compared, with the Kriging algorithm achieving the best accuracies (r = 0.99 and R2 = 0.98) and SVM achieving the second best. A total of 50,905 data points representing the complex multidimensional design space are predicted via the machine-learned models to benefit the future perovskite studies. In addition, the symbolic regression based on the genetic algorithms effectively and automatically designs hybrid descriptors that outperform the individual descriptors. This article highlights the machine learning and symbolic regression methods for designing stable and high-performance halide perovskite materials and serves as a platform for further experimental optimization of halide perovskite materials.

Photoelectrochemical Properties, Machine Learning, and Symbolic Regression for Molecularly Engineered Halide Perovskite Materials in Water.

Defect states at the surface and grain boundaries of perovskite films have been known to be major determinants impairing the optoelectrical properties of perovskite films and the stability of perovskite solar cells (PeSCs). Herein, an n‐type conjugated small‐molecule additive based on fused‐unit dithienothiophen[3,2‐b]‐pyrrolobenzothiadiazole‐core (JY16) is developed for efficient and stable PeSCs, where JY16 possesses the same backbone as the widely used Y6 but with long‐linear n‐hexadecyl side chains rather than branched side chains. Upon introducing JY16 into the perovskite films, the electron‐donating functional groups of JY16 passivate defect states in perovskite films and increase the grain size of perovskite films through Lewis acid–base interactions. Compared to Y6, JY16 exhibits superior charge mobility owing to its molecular packing ability and prevents decomposition of perovskite films under moisture conditions owing to their hydrophobic characteristics, improving the charge extraction ability and moisture stability of PeSCs. Consequently, the PeSC with JY16 shows a high power conversion efficiency of 21.35%, which is higher than those of the PeSC with Y6 (20.12%) and without any additive (18.12%), and outstanding moisture stability under 25% relative humidity, without encapsulation. The proposed organic semiconducting additive will prove to be crucial for achieving highly efficient and moisture stable PeSCs.

https://scholarworks.unist.ac.kr/bitstream/201301/60175/1/Advanced%20Science%20-%202022%20-%20Hong%20-%20Efficient%20and%20Moisture%E2%80%90Stable%20Inverted%20Perovskite%20Solar%20Cells%20via%20n%E2%80%90Type.pdf

Efficient and Moisture‐Stable Inverted Perovskite Solar Cells via n‐Type Small‐Molecule‐Assisted Surface Treatment

4-tert-butylpyridine (TBP) is an indispensable additive for the hole transport layer in highly efficient perovskite solar cells (PSCs), while it can induce corrosion decomposition of perovskites and de-doping effect of spiro-OMeTAD, which present huge challenge for the stability of PSCs. Herein, halogen bonds provided by 1,4-diiodotetrafluorobenzene (1,4-DITFB) are employed to bond with TBP, simultaneously preventing perovskite decomposition and eliminating de-doping effect of oxidized spiro-OMeTAD. Various characterizations have proved strong chemical interaction forms between 1,4-DITFB and TBP. With the incorporation of halogen bonds, perovskite film can maintain initial morphology, crystal structure, and light absorbance; meanwhile, the spiro-OMeTAD film shows a relatively stable conductivity with good charge transport property. Accordingly, the device with TBP complex exhibits significantly enhanced stability in N2 atmosphere or humidity environment. Furthermore, a champion power conversion efficiency of 23.03% is obtained since perovskite is no longer damaged by TBP during device preparation. This strategy overcomes the shortcomings of TBP in n-i-p PSCs community and enhances the application potential of spiro-OMeTAD in fabricating efficient and stable PSCs. 

/pdf/overcoming-perovskite-corrosion-and-de-doping-through-1vxf24c7.pdf

Yuheng Song

Papers

A critical review on the moisture stability of halide perovskite films and solar cells