Fig. 4: Stability of tandem devices.

a Cross-sectional SEM images of perovskites on STS substrates, named as control, and ITS (SiOX) substrates, named as target after heat treatments. b Ten STS and ITS(SiOX) tandem devices aged under 85% RH/ 85 °C with photovoltaic parameters shown. The inset image is the photograph of an encapsulated tandem device. c The MPPT tracking of encapsulated tandem devices at different temperatures in N2.