Recombination and localization: Unfolding the pathways behind conductivity losses in Cs2AgBiBr6 thin films

Abstract

Cs 2 AgBiBr 6 (CABB) has been proposed as a promising nontoxic alternative to lead halide perovskites. However, low charge carrier collection efficiencies remain an obstacle for the incorporation of this material in optoelectronic applications. In this work, we study the optoelectronic properties of CABB thin films using steady state and transient absorption and reflectance spectroscopy. We find that optical measurements on such thin films are distorted as a consequence of multiple reflections within the film. Moreover, we discuss the pathways behind conductivity loss in these thin films, using a combination of microsecond transient absorption spectroscopy and time-resolved microwave conductivity measurements. We demonstrate that a combined effect of carrier loss and localization results in the conductivity loss in CABB thin films. Moreover, we find that the charge carrier diffusion length and grain size are of the same order of magnitude. This suggests that the material's surface is an important contributor to charge-carrier loss.

Design and Performance Exploration of a Lead‐Free All‐Inorganic Hydrogenated Cs2AgBiBr6‐Based Double Perovskite Solar Cell: A Numerical Modeling Study

“…The carrier drift‐diffusion equations are shown as followswhere D n / D p is the electron/hole diffusion coefficient, and μ n / μ p is the electron/hole mobility. In addition, the light absorption coefficient α of the HCABB is extracted from the literature (See Supporting Information), [ 34,72,73 ] while the α of the transport layer material is calculated from the light absorption model equation in SCAPS as follows [ 60,61,74–76 ] where A and B are constants (usually A is 10 5 and B is 0), h is Planck's constant, ν is the photon frequency, and E g is the bandgap of the absorber layer.…”

“…where D n /D p is the electron/hole diffusion coefficient, and μ n /μ p is the electron/hole mobility. In addition, the light absorption coefficient α of the HCABB is extracted from the literature (See Supporting Information), [34,72,73] while the α of the transport layer material is calculated from the light absorption model equation in SCAPS as follows [60,61,[74][75][76] αðλÞ…”

Overcoming the Performance Limitation of Cs2AgBiBr6 Double Perovskites Using Bifacial Photovoltaic Design

“…[ 14 ] Although the absorption coefficient of polycrystalline Cs 2 AgBiBr 6 thin films is relatively strong for photon energies above 2.25 eV, it subsequently becomes weak for energies between 2.25 and 1.83 eV. [ 15 ] As a result, Cs 2 AgBiBr 6 perovskites require an optically thick film to absorb photons efficiently (550–670 nm). In this aspect, they resemble crystalline silicon (c‐Si) semiconductors.…”

Halide Double-Perovskite Semiconductors beyond Photovoltaics

“…As an example, the non-mobile charges in Cs 2 AgBiBr 6 have a spectacularly long lifetime, exceeding tens of microseconds. 55 If these long-lived charges reside at the surface of the crystallites, these may, depending on their absolute energy, be used for photoredox chemistry. Although some promising first results have been obtained in this research area, 23 the use of halide double perovskites for photoredox catalysis has been largely underexplored.…”

“…On the other hand, the presence of trap states may turn out to be beneficial for some of the envisioned applications of halide double perovskites. As an example, the non-mobile charges in Cs 2 AgBiBr 6 have a spectacularly long lifetime, exceeding tens of microseconds . If these long-lived charges reside at the surface of the crystallites, these may, depending on their absolute energy, be used for photoredox chemistry.…”