Role of Self-Trapped Excitons in the Broadband Emission of Lead-Free Perovskite-Inspired Cu₂AgBiI₆

Abstract

The perovskite-inspired Cu 2 AgBiI 6 (CABI) absorber shows promise for lowtoxicity indoor photovoltaics. However, the carrier self-trapping in this material limits its photovoltaic performance. Herein, we examine the self-trapping mechanism in CABI by analyzing the excited-state dynamics of its absorption band at 425 nm, which is responsible for the self-trapped exciton emission, using a combination of photoluminescence and ultrafast transient absorption spectroscopies. Photoexcitation in CABI rapidly generates charge carriers in the silver iodide lattice sites, which localize into the self-trapped states and luminesce. Furthermore, a Cu−Ag−I-rich phase that exhibits similar spectral responses as CABI is synthesized, and a comprehensive structural and photophysical study of this phase provides insights into the nature of the excited states of CABI. Overall, this work explains the origin of self-trapping in CABI. This understanding will play a crucial role in optimizing its optoelectronic properties. It also encourages compositional engineering as the key to suppressing self-trapping in CABI.

Dissecting the Role of the Hole-Transport Layer in Cu2 AgBiI6 Solar Cells: An Integrated Experimental and Theoretical Study

“…The steady-state PL quenching measurements were carried out on CABI|HTL films to investigate the hole extraction ability of the polymeric HTLs (Figure a). The broad emission spectrum of CABI peaked at 723 nm, which closely matches that of CABI (i.e., 720 nm) from our previous studies . P3HT coating led to higher quenching of the emission intensity of poly-TPD and PTAA atop CABI.…”

“…The broad emission spectrum of CABI peaked at 723 nm, which closely matches that of CABI (i.e., 720 nm) from our previous studies. 31 P3HT coating led to higher quenching of the emission intensity of poly-TPD and PTAA atop CABI. This suggests better hole charge extraction in the P3HT case, i.e., a rapid hole injection from the CABI layer to the P3HT, which clearly reflects the enhanced current density of P3HT HTL-based CABI devices.…”

Halide Engineering in Mixed Halide Perovskite-Inspired Cu2AgBiI6 for Solar Cells with Enhanced Performance

“…A positive excited-state absorption (ESA) band with a fast lifetime of 0.31 ps located at 630−750 nm in pristine CABI decreases in amplitude for CABI-5Br and is not observed for any sample with a larger Br content. Based on previous TA studies of CABI films, 11,15,42 this ESA band is assigned to be the existence of STEL states, suggesting that the introduction of Br at the I site can indeed mitigate or even eliminate the formation of self-trapped excitons at the lattice level. In addition, a photobleaching (PB) band is observed centered at 600 nm for pristine CABI and, to a lesser extent, CABI-5Br.…”

Synthesis and Optical Properties of Potassium‐Based Wide‐Bandgap Mixed–Halide Perovskite KPbF2Cl Nanorods

“…We should also mention here that the unintentional doping of C and O may not participate in the STE process, instead, the structural defects and/or impurities can create some non-radiative channels. [46,47,49] Also, the variable nanorod shape of the material can have influence on the deformation and so the PL emission. Our results in Figure 8a show that the relative intensity ratio between E PL1 and E PL2 is changing with excitation wavelength.…”