Exploring the Structural and Photophysical properties of Tri-cation Mixed Halide Double Perovskite (Cs2AgIn0.85-XCeXBi0.15Cl6) for High Performance Phosphor-based WLED

Abstract

Due to their superior optoelectronic properties, lead-free halide double perovskites (HDPs) have been extensively studied in a wide range of optoelectronic applications, especially in white light-emitting diodes (WLED). Focused on white light emission, the HDP structure’s dual octahedral configuration facilitates more lattice distortion, thereby fostering strong electron-phonon coupling derived self-trapped exciton (STE) emission upon photo-excitation. Herein, we propose to fabricate a highly feasible and easily fabricated phosphor-converted white light LED followed by an intensive pre-analysis of the structural, compositional and photophysical properties of the tri-cation mixed halide double perovskite. We have chosen the Cs2AgIn0.85Bi0.15Cl6 compound, as this composition exhibits high stability, direct-allowed transition, and notable photoluminescence quantum yield, which could be a potential candidate for electroluminescent based White light LED devices. However, we have incorporated lanthanide ion (Ce3+) into this cubic HDPs structure via tri-cation mixing at the B” site (Cs2AgIn0.85-XCeXBi0.15Cl6) to internally disturb the structural periodicity, and further enhance the STE emission. Initially, powder XRD revealed the lattice expansion induced by Ce3+ incorporation, XPS and TEM verified the substitution of Ce3+ at In3+site. Meanwhile compositional and optical studies have established the role of Ce3+ in retaining the direct allowed transition by effectively replacing the In3+site. The Urbach energy (EU), a measure of energetic disorderness at the band edges found to be significantly reduced value of 135 meV for Ce 5%. Most significantly, PL emission studies have shown an appreciable enhancement in the PL intensity with a prolonged STE lifetime of 670 ns for Cs2AgIn0.80Ce0.05Bi0.15Cl6, indicating the improved radiative recombination. Besides, excitation dependent Pl and PLE studies reveals that the emission is solely from STE states. Elaboratively, vibrational studies elucidated that Ce 5 % has restabilized elpasolite structure and enhanced the lattice phonons, which ultimately helped in boosting the STE emission as proven by Huang Rhys factor. Finally, an efficient and durable phosphor-converted WLED has been fabricated and its performance was assessed to exhibit CIE (0.35,0.32), CCT= 4368K, and an extremely high CRI, Ra= 92. Thus, our work provides an exclusive strategy to be employed to enhance the STE emission and applied potentially in electroluminescent-based WLED devices.