Severe Morphological Deformation of Spiro-OMeTAD in (CH₃NH₃)PbI₃ Solar Cells at High Temperature

The hole transport material, spiro-OMeTAD, in MAPbI3 perovskite solar cells undergoes severe morphological deformation at high temperature, showing big voids in the layer when the devices are heated at 80 °C and above. It is puzzling that the voids emerge only in the area where the spiro-OMeTAD is capped with Au film and only in the case where the HTM contains both LiTFSI and TBP as additives.