Fig. 4: The formation of HC, their interactions, and finally the cooling down to lattice temperature.

In this image, “HC” refers to hot electrons. A similar phenomenon takes place for hot holes as well. a Absorption of high-energy photons by a photoabsorber. b Electrons from the valence band maximum (VBM) of an absorber material jump to energy states higher than conduction band minimum (CBM). The detailed phenomenon of HC is presented in (c): (i) carrier–carrier scattering, (ii) the thermalization of HC to occupy energy states through Fermi–Dirac distribution, (iii) cooling through their interaction with LO phonons, and (iv) finally the loss of their energy to attain lattice temperature. d The charge carrier either transfer to the electron-transport layer (ETL) or recombination takes place