Growth and passivation of halide perovskite

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Xiu, Jingwei (2022). Growth and passivation of halide perovskite. University of Birmingham. Ph.D.

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Abstract

The all-inorganic halide perovskite (CsPbI\(_3\)) holds promise for photovoltaic applications but suffers from a detrimental phase transformation to a non-perovskite phase δ-CsPbI\(_3\) at low-temperature. The synthesis and stabilization routes to this and other all-inorganic halide perovskites are still not ideal, requiring uneconomical elimination of humidity, toxic solvent or high-temperature quenching.

The all-solid-state synthesis method is a kind of green method to avoid the use of expensive and hazardous solvents. We have studied the influence of inorganic element doping and find that, on the one hand, the incorporation of other metal ions such as Bi\(^{3+}\) and Mn\(^{2+}\) makes little contribution to the stabilization of CsPbI\(_3\); on the other hand, these ions seems to aid the formation of yellow phase at lower temperature and accelerate the decomposition of yellow phase into CsI and PbO at high temperature. Br- doping is able to stabilize CsPbI\(_3\) in air only for a few minutes to an hour, which lead to some observation of cubic phase in the PXRD pattern. Interestingly, a cubic phase dominant black powder can be obtained by the synergic contribution of Br\(^-\) and MA\(^+\)/FA\(^+\) cations.

We also studied the synthesis of CsPbI\(_3\) in air atmosphere at room temperature by solvent method. Water/moisture is commonly meticulously avoided due the fact that it can accelerate the detrimental degradation of the perovskite. In our work, we used an alternative approach of engineering an in situ degradation process to form a dual-functional PbI(OH) protective covering and succeeded in performing the first room-temperature synthesis of γ-CsPbI\(_3\) under ambient humidity. The vastly improved stability benefits from both lattice anchoring and physical coverage of γ-CsPbI\(_3\) by an ultra-thin PbI(OH) layer. The resultant γ-CsPbI\(_3\) is stable for more than 2 months under ambient conditions (25 °C, RH 30 - 60%).

Anti-solvent assistanted crystallization (ASAC) is one the most commonly used methods for the deposition of high-quality perovskite solar cells, where anti-solvents are working to modulate the nucleation process of perovskite films by removing the host solvents, such as N,N-Dimethylformamide (DMF), Dimethyl sulfoxide (DMSO), γ-butyrrolactone (GBL). Their toxicity become a concern during the commercialization process of perovskite solar cells. Various green anti-solvents have appeared in recent years, aiming to reduce the hazardous pollution to human and environment during large-scale industrial production. However, limited green solvents, such acetic ether, anisole and so on, are proven to be efficient to reduce the dependence to the widely used toxic chlorobenzene (CB) and toluene (Tol). One of the most essential reasons is that the green anti-solvent couldn’t satisfy the strict requirement of the self-nuclei process in high-quality perovskite films. To overcome this obstacle and establish more choices for green anti-solvents, we reduce the dependence of perovskite films to self-nuclei process, by adding perovskite CsPbI\(_3\) NCs as artificial seeds. When CsPbI\(_3\) NCs are added along with the alkane anti-solvents, the NCs could compensate the self-nuclei deficit and result in a high crystalline and dense film for high-efficiency perovskite solar cell.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):