Lead halide perovskites are a fascinating class of material for solar cell related applications, which shows record efficiency in the recent past. However, poor thermal and chemical stability prevent industrial applications. The current study describes a thermal stability enhancement of the methyl ammonium lead iodide (MAPbI3) perovskites by an adsorbed layer of formic acid. A MAPbI3 perovskite thin film was spin-coated at ambient pressure (employing methylammonium triiodo plumbate as the precursor) on an Indium Tin Oxide (ITO) coated glass substrate, characterized at ambient utilizing UV-Visible spectroscopy and at ultra-high vacuum (UHV) by Auger electron spectroscopy (AES). Thermal stability of the perovskite thin film was investigated employing UHV multi-mass thermal desorption spectroscopy (TDS) together with AES, in the presence and the absence of an adsorbed layer of formic acid. According to multi-mass TDS, as synthesized perovskite thin films starts to degrade at about 540 K under UHV. AES indicates complete degradation of the perovskite thin film after heating to ~750 K. The same heating ramp was applied in the presence of an adsorbed formic acid molecular layer on the perovskite thin film. A significant amount of the perovskite thin film was retained according to AES, which suggests that the molecular layer of formic acid enhanced the thermal stability of the perovskite thin film significantly. Density functional theory (DFT) based thermalized molecular dynamics (MD) calculations are performed to further investigate the adsorption of carbon dioxide (CO2) and formic acid (HCOOH) on methylammonium lead iodide (MAPbI3) perovskite surfaces. Our calculations indicate that for both species adsorption events on MAI-terminated surfaces take place at higher temperature than that on PbI2-terminated surfaces. In addition, it is found that HCOOH is more likely to be adsorped on surfaces than CO2 due to hydrogen bonding interactions.

Thermal stability enhancement of methyl ammonium lead iodide perovskites with formic acid adsorption: An ultra-high vacuum based experimental study

256th National Meeting (2018)

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