Also the temperature plays an important role: while MAPbI
3 has a reported decomposition temperature of 300°C [
66], the decomposition to PbI
2 at surfaces or grain boundaries has been found to occur at much lower temperatures as 150°C [
138] and even 105°C [
139]. More worrying, MAPbI
3 presents two crystalline phase transition around −111
oC and 57°C, from orthorhombic to tetragonal and from tetragonal to cubic, respectively [
65,
66,
140]. Regarding the first, the work by Jacobson et al. [
141] discarded space applications due to the drastic PCE reduction toward the orthorhombic phase; while also recommended room temperature as the most profitable. On the other hand, considering that under sunny summer days the panels can reach over 80°C, the crystal instability of MAPbX
3 (X−Cl, Br, I) has gained the attention of several studies, as summarized by Niu et al. [
142].
Anyway, there is still extensive research ongoing to understand the different and dominant PSCs degradation pathways, but clearly it was the moisture possibly the first major factor identified to affect MAPbI
3 stability in PSCs [
143]. For preventing this, a primary strategy has been focused on the guarding and protecting of the absorber from external assaults by developing specialized functional barrier structures [
144].
of surface-adsorbed oxygen, which was not present in meso-TiO
2 free devices. On the other hand, J.A. Christians et al. [
149] found superior photocurrent stability when substituting spiro-OMeTAD by CuI. Also a tetrathiafulvalene derivative (TTF-1) as HTM was introduced by J. Liu et al. [
150] as a stability improver. A more central change in the device architecture was proposed by S. Aharon et al. [
151] who obtained best stability with FAPbI
3 as absorber material. The role of interface in stability is nicely reviewed in the article by Manspeaker et al. [
152].