Enhancing the Microstructure of Perovskite‐Inspired Cu‐Ag‐Bi‐I Absorber for Efficient Indoor Photovoltaics

Abstract

Lead‐free perovskite‐inspired materials (PIMs) are gaining attention in optoelectronics due to their low toxicity and inherent air stability. Their wide bandgaps (≈2 eV) make them ideal for indoor light harvesting. However, the investigation of PIMs for indoor photovoltaics (IPVs) is still in its infancy. Herein, the IPV potential of a quaternary PIM, Cu2AgBiI6 (CABI), is demonstrated upon controlling the film crystallization dynamics via additive engineering. The addition of 1.5 vol% hydroiodic acid (HI) leads to films with improved surface coverage and large crystalline domains. The morphologically‐enhanced CABI+HI absorber leads to photovoltaic cells with a power conversion efficiency of 1.3% under 1 sun illumination—the highest efficiency ever reported for CABI cells and of 4.7% under indoor white light‐emitting diode lighting—that is, within the same range of commercial IPVs. This work highlights the great potential of CABI for IPVs and paves the way for future performance improvements through effective passivation strategies.

Perovskite-inspired Cu2AgBiI6 for mesoscopic indoor photovoltaics under realistic low-light intensity conditions

“…The champion CABI-Meso device delivers a PCE of 1.26%, which is comparable with the highest PCE values reported for the CABI planar and mesoscopic solar cells fabricated with the same metal electrode (i.e., Au). 18,24,25 The FF value of 72% of CABI-Meso device (Figure 2b) is markedly the highest FF ever achieved for a CABI solar cell fabricated with the same metal electrode. 18,20,24,25 The external quantum efficiency (EQE) values of this device are ⁓29% and 18% at 370 nm and 580 nm, respectively (Figure S3), which are comparable to the values reported earlier for CABI.…”

“…18,24,25 The FF value of 72% of CABI-Meso device (Figure 2b) is markedly the highest FF ever achieved for a CABI solar cell fabricated with the same metal electrode. 18,20,24,25 The external quantum efficiency (EQE) values of this device are ⁓29% and 18% at 370 nm and 580 nm, respectively (Figure S3), which are comparable to the values reported earlier for CABI. 18,24 The short-circuit current density (J SC ) value (from current density (J)-voltage (V) scans) of 3.0 mA cm -2 of the champion device closely matches the value extracted from its EQE spectrum (2.9 mA cm -2 ).…”

“…The lower bismuth and iodine compositional values can be partially attributed to the presence of Cu 2 BiI 5 impurities (Figure 1a) and the possible evaporation of iodine under strong electron beam exposure. 18 The optical absorption spectra of the CABI films show a peak related to CABI at ⁓580 nm and an unassigned peak at 420 nm (Figure S1 of the Electronic Supplementary Information, SI). 18 The films have a direct band gap of 1.91 eV, as extracted from their absorption edges in the Tauc plots of Figure 1b.…”

“…18 The optical absorption spectra of the CABI films show a peak related to CABI at ⁓580 nm and an unassigned peak at 420 nm (Figure S1 of the Electronic Supplementary Information, SI). 18 The films have a direct band gap of 1.91 eV, as extracted from their absorption edges in the Tauc plots of Figure 1b. The examination of the emission properties of the films reveals their weak and broad photoluminescence (PL) signal that peaks at 715 nm (Figure 1c).…”

“…3,10 Yet, the field is in its early infancy and only a few pnictohalides-based PIMs have been investigated for use in IPVs, such as antimony (Sb)-based PIMs and silver iodobismuthates. 5,10,18 Notably, the IPV efficiencies of the pnictohalides-based PIMs reported to date has been up to 5%, 5,10,18 which is already in the range of mainstream commercial IPV based on amorphous silicon. Given the considerably higher maximum efficiency, these results prompt the investigation of materials and device engineering strategies to bridge the gap to their ultimate theoretical IPV efficiencies.…”