Thermodynamic origin of instability in hybrid halide perovskites.

E. Tenuta,C. Zheng,O. Rubel

doi:10.1038/srep37654

Abstract

Degradation of hybrid halide perovskites under the influence of environmental factors impairs future prospects of using these materials as absorbers in solar cells. First principle calculations can be used as a guideline in search of new materials, provided we can rely on their predictive capabilities. We show that the instability of perovskites can be captured using ab initio total energy calculations for reactants and products augmented with additional thermodynamic data to account for finite temperature effects. Calculations suggest that the instability of CH3NH3PbI3 in moist environment is linked to the aqueous solubility of the CH3NH3I salt, thus making other perovskite materials with soluble decomposition products prone to degradation. Properties of NH3OHPbI3, NH3NH2PbI3, PH4PbI3, SbH4PbI3, CsPbBr3, and a new hypothetical SF3PbI3 perovskite are studied in the search for alternative solar cell absorber materials with enhanced chemical stability.

Highlights

Degradation of hybrid halide perovskites under the influence of environmental factors impairs future prospects of using these materials as absorbers in solar cells
A recently emerged class of hybrid halide perovskite materials holds a promise to lead the way towards low-cost photovoltaic devices as they combine an energy conversion efficiency of nearly 20% with a low-temperature solution a combination of various porrogcaensiscincgattieocnhsnXo+lo =gy(1C–4H
We begin by examining the chemical stability of CH3NH3PbI3 against decomposition

Summary

Results and Discussion

In this calculation, we shall assume that all structures decompose following the pathway similar to Eq (1) with the exception of SF3PbI3. Results for the decomposition reaction enthalpy calculated using Eq (3) are given, where the compounds are sorted in the order of increasing ∆H0oK (higher values favour stability of perovskites). Unlike CH3NH3PbI3, the decomposition reaction enthalpy of CsPbBr3 is high (Table 2) Assuming that both compounds have the same magnitude of the final temperature contribution ∆μ 3o00K to the free energy, one would expect the free energy of CsPbBr3 to be approximately 0.5 eV/f.u. lower than that for decomposition products (PbBr2 and CsBr) indicating strong chemical stability of CsPbBr3 against spontaneous decomposition. CsPbBr3 can be attributed to the greater value of ∆G3o00K, which translates into a much lower saturation concentration of CsBr cs ~ 60 μM as compared to cs ~ 50 mM for CH3NH3I (see discussion in the preceding subsection)

Conclusions

Author Contributions

Additional Information