Intrinsic thermal decomposition pathways of lead halide perovskites APbX3

We present a systematic study on intrinsic thermal stability of a series of complex lead halides APbX(3), used as absorber materials in perovskite solar cells. Mechanistically, the perovskites APbX(3) were shown to decompose under thermal stress conditions initially to form PbX2 and AX salts. Thermolysis of the latter yields multiple volatile products, which were analyzed by mass spectrometry. We reconfirmed the CH3I + NH3 decomposition route for MAPbI(3) and observed for the first time CH4, ethylene and HI (formed from CH3I). In case of FAPbI(3), the formation of 2-aminomalononitrile (not 1,3,5-triazine as reported recently) was revealed along with NH4I and HCN. Importantly, the stability of the lead halide perovskites shows a good correlation with the volatility of univalent cation halides (or their decomposition products) incorporated in their structure. In particular, MAPbX(3) have the lowest stability since they incorporate the most volatile (or easy to decompose) methylammonium halides MAX. On the contrary, all-inorganic CsPbX3 show remarkable compositional stability since CsBr and CsI are non-volatile under the solar cell operation conditions. The established relationship and material decomposition pathways provide important guidelines for rational design of novel absorber materials for perovskite solar cells with improved thermal stability suitable for terrestrial and space applications.