(The electron barrier is an energy barrier that prevents or slows down the movement of electrons across an interface between two materials. It occurs due to a difference in energy levels when two materials come into contact.
Different materials have different Fermi levels. To balance out, electrons move from the higher-energy side to the lower-energy side. This movement bends the bands and creates an electric field that can help guide charges in a solar cell.)
Hole diffusion occurs from the perovskite layer((BA0.5PEA0.5)2FA3Sn4I13) to the PEDOT:PSS layer under illumination and resulting electron barrier reduction.
Under illumination, the electrons are injected from perovskite to PEDOT:PSS which recombine with bipolarons and form localized polarons near the interface, which results in an increased Nspin and enhanced electron barrier and improves Voc and better performance of solar cell (Here bipolaron is formed when two similar charges bind together within a material. In PEDOT:PSS, bipolarons are created when two holes pair up in the polymer chain).
To measure change of charge states under illumination, researchers analyzed ESR spectra using a least-squares method. Here Lorentzian and Gaussian formulas are used to describe the ESR spectra of semiconductor materials.
https://www.nature.com/articles/s41528-024-00376-2
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