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

Abstract

Perovskite-inspired Cu2AgBiI6 (CABI) absorber has recently gained increased popularity due to its low toxicity, intrinsic air stability, and wide bandgap ≈ 2 eV, which makes it ideal for indoor photovoltaics (IPVs). However, the considerable presence of both intrinsic and surface defects is responsible of the still modest indoor power conversion efficiency (PCE(i)) of CABI- based IPVs, with the short-circuit current density (JSC) being nearly half of the theoretical limit. Herein, we introduce antimony (III) (Sb3+) into the octahedral lattice sites of CABI structure, leading to CABI-Sb with substantially larger crystalline domains than CABI. The alloying of Sb3+ with bismuth (III) (Bi3+) induces changes in the local structural symmetry, in turn causing a remarkably increased formation energy of intrinsic defects. This accounts for the overall reduced defect density in CABI-Sb. CABI-Sb IPVs feature an outstanding PCE(i) of nearly 10% (9.53%) at 1000 lux, which represents an almost double PCE(i) compared to that of CABI devices (5.52%) mainly due to an improvement in JSC. This work will promote future compositional design studies to reduce the intrinsic defect tolerance of next-generation wide- bandgap absorbers for high-performance and stable IPVs.

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

“…This suggests the involvement of Bi lattice sites in CABI emission. This is in line with the suppression of the STE emission through partial substitution of Sb 3+ into [BiI 6 ] 3– units of CABI crystal structure, which, in turn, suggests that distortion of [BiI 6 ] 3– in the excited state produces the STE state. Moreover, the bottom of the conduction band of CABI is dominated by Bi 6p and I 5p states .…”

“…These findings suggest a complex STE emission mechanism occurring in CABI. Very recently, by coalloying antimony(III) (Sb 3+ ) with Bi 3+ in CABI, we successfully quenched the STE emission of CABI, in turn significantly boosting the J SC of CABI-Sb IPVs, which achieved a bold PCE(i) of nearly 10% . This clearly suggests that the suppression of the self-trapping of the charge carriers is crucial to enhance the performance of CABI-based devices.…”

“…Being the front runner in the lead-free PIMs for IPVs, understanding the basis of the carrier self-trapping in CABI will direct its further optimization for various charge extraction-based applications (photovoltaics, X-ray detectors, and photoelectrochemical fuel generation) and the discovery of materials with similar optoelectronic properties. Since our proposed carrier trapping mechanism involves [BiI 6 ] 3– units, the partial alloying of the Bi 3+ lattice sites with smaller or larger cations or the I – ions with other halide ions may alter the local structural symmetry , and mitigate the intrinsic carrier trapping pathways, in turn improving the performance of photovoltaic devices. Our findings will stimulate novel theoretical and/or experimental investigations for optimizing low-dimensional lead-free PIMs through compositional engineering.…”

Roadmap on energy harvesting materials

“…Fulfilling this prediction, AgBiI 4 -based indoor photovoltaics with an efficiency of up to 5.2% was subsequently demonstrated [81]. Most recently, emerging Cu-Ag-Bi-I-based absorbers with near optimum bandgap for indoor photovoltaics have been shown to deliver PCE(i) values of up to 9.53% [82][83][84], thereby highlighting the considerable indoor photovoltaic potential of copper-silver pnictohalides [79]. Furthermore, a hybrid absorber combining Cs 3 Sb 2 I 9 and an organic molecule, ITIC, was reported to deliver PCE(i) values of up to 9.2% [85].…”

Lead-free perovskite-inspired semiconductors for indoor light-harvesting – the present and the future

“…However, the low indoor V OC values of just B0.6 V in these devices are due to already low V OC values achieved under 1-Sun, particularly in the case of CABI. [24][25][26]28 Hoye and co-workers examined the performance limiting factors of Cs 2 Ag(Sb x Bi 1Àx )Br 6 solar cells. 54 They demonstrated that sub-band gap states are accountable for the V OC losses.…”