Enhancing blue light excitation in Pb-free double perovskites by decreasing the energy barrier of the self-trapping exciton and prospects for environment-friendly optoelectronic applications

Abstract

In Pb-free double perovskites (DPs) optoelectronic material systems, the energy barrier ∆Eb suppression between free excitons (FEs) and self-trapped excitons (STEs) makes it difficult to achieve blue-light excitation even as the bandgap narrows, which has become a major challenge in the development of full-colour displays, lighting, optoelectronics and catalytic technologies. Here, Cs2-aKaAg0.6Na0.4In0.8Bi0.2Cl6-x-yBrx(SH)y DPs, prepared by doping with HS- (hydrosulfide ion), Br- and K+, achieve a blue excitation at 468 nm. The octahedral tilt caused by doping with K+, Br- and HS- ions reduces the local crystal dimensions and thus the energy barrier ∆Eb. The aggregation of electrons around the AgX6 octahedron under the action of HS- contributes to the formation of effective STE emission under blue light excitation. Furthermore, the potential impact of blue-light-excited Cs2-aKaAg0.6Na0.4In0.8Bi0.2Cl6-x-yBrx(SH)y DPs on enhancing the power conversion efficiency (PCE) of photovoltaic modules and the photodegradation efficiency of Rhodamine B (RhB) is explored. The study concludes by highlighting the wide-ranging applications in displays, photovoltaics, and photocatalytic degradation that could be realized through the utilization of blue-light-excited Pb-free DPs.