Superior Photovoltaic Properties of Lead Halide Perovskites: Insights from First-Principles Theory

Abstract

Organic-inorganic methylammounium lead halide perovskites have recently emerged as promising solar photovoltaic absorbers. In this feature article, we review our theoretical understanding of the superior photovoltaic properties, such as the extremely high optical absorption coefficient and very long carrier diffusion length of CH 3 NH 3 PbI 3 perovskites through first-principles theory. We elucidate that the superior photovoltaic properties are attributed to the combination of direct band gap p-p transitions enabled by the Pb lone-pair s orbitals and perovskite symmetry, high iconicity, large lattice constant, and strong antibonding coupling between Pb lone-pair s and I p orbitals. We show that CH 3 NH 3 PbI 3 exhibits intrinsic ambipolar self-doping behavior with conductivities tunable from p-type to n-type via controlling the growth conditions. We show that the p-type conductivity can be further improved by incorporating some group IA, IB, or VIA elements at I-rich/Pb-poor growth conditions. However, the n-type conductivity cannot be improved under thermal equilibrium growth conditions through extrinsic doping due to the compensation from intrinsic point defects.

Solution-processed visible-blind UV-A photodetectors based on CH3NH3PbCl3 perovskite thin films

“…47 By investigating the trap states that could be formed by all possible intrinsic point defects in CH3NH3PbI3, it was found that Pb vacancies can pull up the valence band and Pb interstitials can pull down the conduction band, which would finally result in a narrower band gap. [48][49][50] Experimental results showed hole traps at the surface of CH3NH3PbI3 thin films and excitonic traps below the optical gaps in these materials, which are likely caused by electron-phonon coupling, especially at surfaces/interfaces of crystalline perovskites. 51 The electron paramagnetic resonance (EPR) studies also showed that in perovskites organic cations that deprotonate from their oxidized state, Pb 2+ cations as Pb 3+ centers trap holes while Pb 2+ cation clusters trap electrons.…”

“…The formation of trap states in CH3NH3PbI3 has been investigated computationally [47][48][49][50] and experimentally. 15,51,52 Elemental defects derived from Frenkel defects, such as Pb, I, and CH3NH3 vacancies, form shallow levels near band edges, which play the role of unintentional doping sources.…”

Metal halide perovskites for energy applications

“…In addition to the well-known properties of perovskites, a unique feature that makes perovskites so good for PV applications relies on the fact that the energy of many electronic defects is expected to be close to the continuum of states within the bands, hence not detrimental for performance 47 .…”

Selection Metric for Photovoltaic Materials Screening Based on Detailed-Balance Analysis

“…One of the first and maybe most prominent examples of such a selection metric proposed for computational materials screening is presented by Yu and Zunger in 2012 [37] and has been widely used to estimate efficiency limits in the last years [38][39][40][41][42][43][44][45][46][47][48][49]. In their paper, they proposed a "spectroscopic limited maximum efficiency" SLME selection metric that aims to calculate efficiency limits for non-step like absorption coefficients beyond the radiative limit.…”