Triple A‐Site Cation Mixing in 2D Perovskite‐Inspired Antimony Halide Absorbers for Efficient Indoor Photovoltaics

Abstract

Antimony‐based perovskite‐inspired materials (PIMs) are solution‐processable halide absorbers with interesting optoelectronic properties, low toxicity, and good intrinsic stability. Their bandgaps around 2 eV make them particularly suited for indoor photovoltaics (IPVs). Yet, so far only the fully inorganic Cs3Sb2ClxI9−x composition has been employed as a light‐harvesting layer in IPVs. Herein, the first triple‐cation Sb‐based PIM (CsMAFA‐Sb) in which the A‐site of the A3Sb2X9 structure consists of inorganic cesium alloyed with organic methylammonium (MA) and formamidinium (FA) cations is introduced. Simultaneously, the X‐site is tuned to guarantee a 2D structure while keeping the bandgap nearly unchanged. The presence of three A‐site cations is essential to reduce the trap‐assisted recombination pathways and achieve high performance in both outdoor and indoor photovoltaics. The external quantum efficiency peak of 77% and the indoor power conversion efficiency of 6.4% are the highest values ever reported for pnictohalide‐based photovoltaics. Upon doping of the P3HT hole‐transport layer with F4‐TCNQ, the power conversion efficiency of CsMAFA‐Sb devices is fully retained compared to the initial value after nearly 150 days of storage in dry air. This work provides an effective compositional strategy to inspire new perspectives in the PIM design for IPVs with competitive performance and air stability.

Antimony-bismuth alloying: the key to a major boost in the efficiency of lead-free perovskite-inspired indoor photovoltaics

“…19 Slight improvements in FF and VOC are also observed for the CABI-Sb IPV devices. The PCE(i) of 9.53% for the best CABI-Sb device is the highest value ever reported for IPVs based on lead-free perovskiteinspired absorbers (with the previous record being 6.37% for CsMAFA-Sb pnictohalide 10 ).…”

“…3,4 Perovskite-inspired pnictohalides employing cations from Group VA of the periodic table (e.g., antimony (III) (Sb 3+ ) and bismuth (III) (Bi 3+ )) have recently emerged as promising low-toxicity and highly stable absorbers for IPVs, owing to their bandgap of around 2 eV, which is nearly ideal for indoor light-harvesting. 5,6 However, so far only a small handful of IPV studies have been reported 5,7,8,9,10 with PCE(i) values already in the same range of commercially available hydrogenated amorphous silicon (a-Si:H) devices, 11,12 though still far from the maximum theoretical PCE(i) of 50-60%. 5,6 Indeed, all the reported PCE(i) values stagnate around 5-6% at 1000 lux white light-emitting diode (WLED) illumination, with the highest record being so far 6.4%.…”

“…5,6 Indeed, all the reported PCE(i) values stagnate around 5-6% at 1000 lux white light-emitting diode (WLED) illumination, with the highest record being so far 6.4%. 10 The reasons for such modest efficiencies lie in the low open-circuit voltage (VOC) and short-circuit current density (JSC) values, mainly due to poor charge carrier transport resulting from abundant intrinsic defects and other typical recombination losses in this class of materials, such as self-trapping. 13,14 Despite being one of the most recently discovered pnictohalides, Cu2AgBiI6 (CABI) has already gained an exceptional interest from the photovoltaic and optoelectronic community owing to its direct bandgap, high absorption coefficient, low exciton binding energy, and the desired band gap of ≈ 2 eV for IPVs.…”

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

“…The substantially lowered (i.e., by 2 orders of magnitude) emission lifetime suggests the loss of the majority of the STEs before their radiative recombination through the vibrations (as well as defect-related recombination) at room temperature, thus leading to a very low PLQY. Similarly, various 2D metal halides (e.g., Cs 3 Bi 2 I 9 , Cs 3 Sb 2 I 9 , and Rb 3 Sb 2 I 9 , and (Cs/MA/FA) 3 Sb 2 I 9 ) exhibit broad and very weak STE emission intensities despite the strong charge carrier self-trapping. − Therefore, regardless of the low PLQY (which only provides information about the radiative recombination of the STEs but not the total number of STEs formed), understanding the STE process in CABI, a lead-free PIM for photovoltaic and other optoelectronic applications, is of utmost significance.…”

Surface Defects Passivation with Organic Salt for Highly Stable and Efficient Lead-Free Cs3Sb2I9 Perovskite Solar Cells

“…FTIR spectra for the films showed some typical peaks at 1712 and 3268 cm −1 , which were assigned to the N−H vibration. 27,35 The observed 1626 cm −1 stretching vibration bond corresponds to C�O, 29 and the broad peak at 3442 cm −1 in the pristine sample belongs to O− H. 25 Furthermore, scanning electronic microscopy (SEM) was used to investigate the surface morphology of the pristine Cs 3 Sb 2 I 9 and FAI-Cs 3 Sb 2 I 9 films. Interestingly, compared to the pristine Cs 3 Sb 2 I 9 film, the FAI-Cs 3 Sb 2 I 9 films exhibited comparatively high surface coverage, fewer grain boundaries, and larger grain size (Figure S5).…”