Tuning the Optical Absorption of Sn-, Ge-, and Zn-Substituted Cs2AgBiBr6 Double Perovskites: Structural and Electronic Effects

Paz Sebastiá-Luna,Henk J Bolink,Joaquín Calbo,Enrique Ortí,Michele Sessolo,Nicolás Albiach-Sebastián,Francisco Palazón

doi:10.1021/acs.chemmater.1c02236

Paz Sebastiá-Luna, Henk J Bolink + Show 5 more

Open Access

https://doi.org/10.1021/acs.chemmater.1c02236

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Abstract

Lead-free halide double perovskites (DPs) are highly tunable materials in terms of chemical composition and optical properties. One of the most widely reported DPs is Cs2AgBiBr6, which is envisaged as a promising absorber for photovoltaics. Nevertheless, its bandgap (around 1.9–2.3 eV) remains too large for common tandem solar cells. In this work, we report the mechanochemical synthesis of Sn-, Ge-, and Zn-substituted Cs2AgBiBr6 in powder form; their bandgaps reach 1.55, 1.80, and 2.02 eV, respectively. These differences are rationalized through density functional theory calculations, demonstrating combined electronic and structural (disorder) effects introduced by the divalent metal-cation substituents. Finally, we present the first vacuum-deposited thin films of the Sn-substituted DP, which also show a notable narrowing of the bandgap, and this paves the way toward its implementation in photovoltaic solar cells.

Highlights

Lead halide perovskites (LHPs) have emerged as promising materials for future photovoltaics and other optoelectronic applications
We present the first vacuum-deposited thin films of the Sn-substituted double perovskites (DPs), which show a notable narrowing of the bandgap, and this paves the way toward its implementation in photovoltaic solar cells
We demonstrate the first DP thin films with increased visible absorption, which paves the way for their implementation in photovoltaics and other thin film-based optoelectronic applications

Summary

INTRODUCTION

Lead halide perovskites (LHPs) have emerged as promising materials for future photovoltaics and other optoelectronic applications. Mitzi and co-workers found a bandgap decrease of ∼0.3 eV by the addition of Sb(III), another element with an ns[2] valence electron configuration.[11] In contrast, addition of In(III), with a different electronic configuration [nd[10], same as Ag(I)], was found to increase the bandgap.[11] From these results, a phenomenological rule seems to suggest that ns2-electronic-configuration substituents (Tl+, Sn2+, and Sb3+) cause a decrease in the bandgap of Cs2AgBiBr6, while nd[10] substituents lead to a bandgap increase This observation led us to attempt such bandgap tuning through simpler and faster synthetic methods,[12] along with the introduction of new substituents not previously reported experimentally, in particular Ge2+ and Zn2+, with ns[2] and nd[10] electronic configurations, respectively. We demonstrate the first DP thin films with increased visible absorption, which paves the way for their implementation in photovoltaics and other thin film-based optoelectronic applications

EXPERIMENTAL SECTION

RESULTS AND DISCUSSION

CONCLUSIONS

■ ACKNOWLEDGMENTS

■ REFERENCES