Interface Bridge Engineering for High Efficient Hole Injection in CZTS-Based Perovskite Light-Emitting Diodes

Achieving balanced charge injection and transport in perovskite light-emitting diodes (PeLEDs) remains challenging due to the large energy level offset between the indium tin oxide (ITO) electrode and the hole transport layer, coupled with an unsatisfactory hole injection capability. Given that Cu₂ZnSnS₄ (CZTS) offers a deep valence band maximum, high hole mobility, high stability, and cost-effectiveness. Here, CZTS is introduced as a hole injection layer between the ITO and poly(9-vinylcarbazole) (PVK) layers to align energy level and increase hole injection capacity. The huge difference between CZTS and PVK work functions creates a robust interfacial electric field, resulting in an interfacial dipole effect, which significantly enhancing hole injection and boosting the carrier radiative recombination efficiency. Meanwhile, the robust CZTS/PVK interface favors high-quality FAPbBr₃ films with good morphology and reduced defects. The resulting optimized PeLEDs with a peak emission wavelength of 529 nm achieve an external quantum efficiency (EQE) of 15.44%, a turn-on voltage of 3 V and current efficiency (CE) of 75.3 cd A⁻¹, significantly outperforming the control devices, which exhibit an EQE of 7.55%, a turn-on voltage of 3.4 V and CE of 35.4 cd A⁻¹. This study provides novel insights into constructing efficient PeLEDs through enhanced hole injection using CZTS.