Bistable Amphoteric Native Defect Model of Perovskite Photovoltaics

Abstract

The past few years have witnessed unprecedented rapid improvement of the performance of a new class of photovoltaics based on halide perovskites. This progress has been achieved even though there is no generally accepted mechanism of the operation of these solar cells. Here we present a model based on bistable amphoteric native defects that accounts for all key characteristics of these photovoltaics and explains many idiosyncratic properties of halide perovskites. We show that a transformation between donor-like and acceptor-like configurations leads to a resonant interaction between amphoteric defects and free charge carriers. This interaction, combined with the charge transfer from the perovskite to the electron and hole transporting layers results in the formation of a dynamic n-i-p junction whose photovoltaic parameters are determined by the perovskite absorber. The model provides a unified explanation for the outstanding properties of the perovskite photovoltaics, including hysteresis of J-V characteristics and ultraviolet light-induced degradation.

The Bright Side and Dark Side of Hybrid Organic–Inorganic Perovskites

“…The essential feature of the bistable amphoteric native defects (BANDs) is that they can undergo a structural transformation between the donor and acceptor configuration. The dynamic balance between those two defect configurations is controlled by the concentrations of photoexcited electrons and holes 12 . These properties of BANDs were used to explain formation and the properties of p-i-n junction in perovskite films in contact with electron and hole transporting layers.…”

“…In our calculations we consider MAPbI3 as a prototypical perovskite material with BANDs concentration of 2𝑁 𝑑 . Under equilibrium conditions the material is compensated and has high resistivity with the defects evenly distributed between donor and acceptor configurations, 𝑁 𝐷 + = 𝑁 𝐴 − = 𝑁 𝑑 12 . Illumination of the sample with above the band gap energy monochromatic light produces electron-hole pairs with a narrow energy and kwavector distribution, schematically shown in Figure 1 the radiative bimolecular recombination and the Auger recombination rates because the low energy, "dark" electrons do not encounter the low energy "dark" holes.…”

“…In our first paper 12 we have proposed that the exceptional properties of HOIPs as PV absorbers can be explained by bistable amphoteric native defects (BANDs), a class of defects that can undergo a transformation between shallow donor and shallow acceptor configuration. The BANDs model accounts for a variety of the phenomena observed in HOIPs including formation of p-i-n junction PVs as well as hysteresis of J-V characteristics and reversible UV degradation of PV devices 12 . There is growing evidence showing that the iodine site defects play an important role in determining the photophysical properties and stability of MAPbI3 13,14 .…”

Design and Modelling of Eco-Friendly CH3NH3SnI3-Based Perovskite Solar Cells with Suitable Transport Layers

“…The impact of native imperfections on semiconductors is referred to as an "amphoteric defect" [62]. The fundamental characteristic of this type of defect is the Fermi level stabilization energy (EFS) [63].…”

Electron irradiation induced aging effects on radiative recombination properties of quadruple cation organic-inorganic perovskite layers

“…Some authors suggest that a unique feature of HOIPs is that any dangling bond-like defect or associated defect complexes will have transition states close to the band edges [57]. If this statement is correct, this suggests that the irradiation-aging assisted broadening of the band tails arise from the formation of dangling bond-like defect or associated defect complexes.…”