With the progress in the development of perovskite solar cells, increased efforts have been devoted to enhancing their stability. With more devices being able to survive harsher stability testing conditions, such as damp heat or outdoor testing, there is increased interest in encapsulation techniques suitable for this type of tests, since both device architecture compatible with increased stability and effective encapsulation are necessary for those testing conditions. A variety of encapsulation techniques and materials have been reported to date for devices with different architectures and tested under different conditions. In this Perspective, we will discuss important factors affecting the encapsulation effectiveness and focus on the devices, which have been subjected to outdoor testing or damp heat testing. In addition to encapsulation requirements for these testing conditions, we will also discuss device requirements. Finally, we discuss possible methods for accelerating the testing of encapsulation and device stability and discuss the future outlook and important issues, which need to be addressed for further advancement of the stability of perovskite solar cells.

We report electron emission from (111) surfaces of intrinsic crystalline Ge and Si using 25-ns laser pulses at λ=1.06, 0.53, 0.35, and 0.26 μm. For 0.26 and 0.35 μm, two-photon photoemission is observed, while for 0.53 and 1.06 μm only thermionic emission is obtained. In all cases the emission current follows the temporal profile of the laser pulse up to the melting point. Analysis of the thermionic data, taking account of the nonequilibrium carrier density, indicates that the electron temperature follows, but can be up to several hundred degrees higher than, the lattice temperature, during the laser pulse.