Release of sym-triazine and HCN during the thermal degradation of FA based hybrid perovskites at low T conditions
Controlled thermal degradation experiments of formamidinium-based perovskite and their halide precursors were carried out in helium and vacuum atmosphere under pulsed illumination/dark conditions to simulate working temperature conditions of photovoltaic devices.
The identification of decomposition gas products based on the quadrupole mass spectrometry technique uncovered the release of sym-triazine, formamidine, and hydrogen cyanide (HCN). Meanwhile, sym-triazine was obtained as thermal product of degradation for temperatures above 95 ºC. Below this temperature, only formamidine and HCN generation routes were observed.
Experimental results supported by DFT calculations indicated that formamidinium is more resilient to thermal degradation and release of irreversible decomposition products compared to methylammonium cation because a larger enthalpy and activation energy for the decomposition reactions.
The HCN instantaneous concentration observed during low temperature heating tests and maximum release achievable per meter-square of FA based perovskite based solar cell estimations are compared to acute exposure guideline levels of airborne HCN concentration.