Interfacial Dipole Engineering for Energy Level Alignment in NiOx-Based Quantum Dot Light-Emitting Diodes.

The solution-derived non-stoichiometric nickel oxide (NiOx) is a promising hole-injecting material for stable quantum dot light-emitting diodes (QLEDs). However, the carrier imbalance due to the misalignment of energy levels between the NiOx and polymeric hole-transporting layers (HTLs) curtails the device efficiency. In this study, the modification of the NiOx surface is investigated using either 3-cyanobenzoic acid (3-CN-BA) or 4-cyanobenzoic acid (4-CN-BA) in the QLED fabrication. Morphological and electrical analyses revealed that both 4-CN-BA and 3-CN-BA can enhance the work function of NiOx, reduce the oxygen vacancies on the NiOx surface, and facilitate a uniform morphology for subsequent HTL layers. Moreover, it is found that the binding configurations of dipole molecules as a function of the substitution position of the tail group significantly impact the work function of underlying layers. When integrated in QLEDs, the modification layers resulted in a significant improvement in the electroluminescent efficiency due to the enhancement of energy level alignment and charge balance within the devices. Specifically, QLEDs incorporating 4-CN-BA achieved a champion external quantum efficiency (EQE) of 20.34%, which is a 1.8X improvement in comparison with that of the devices utilizing unmodified NiOx (7.28%). Moreover, QLEDs with 4-CN-BA and 3-CN-BA modifications exhibited prolonged operational lifetimes, indicating potential for practical applications.

Unlocking The Role of Guanidinium Salts in Interface Engineering for Boosted Performance of Inverted Perovskite Solar Cells.

NiOx-based inverted perovskite solar cells (PSCs) have attracted growing attention due to their low cost and large-scale application potential. However, the efficiency and stability of inverted planar heterojunction PSCs is still unsatisfactory owing to insufficient charge-extraction caused by undesirable interfacial contact between perovskite and NiOx hole transport layers (HTLs). Herein an interfacial passivation strategy with guanidinium salts (guanidinium thiocyanate (GuASCN), guanidine hydrobromide (GuABr), guanidine hydriodate (GuAI)) as passivator is employed to solve this problem. We systematically study the effect of various guanidinium salts on the crystallinity, morphology, and photophysical properties of perovskite films. Guanidine salt as interfacial passivator can decrease interface resistance, reduce carrier non-radiative recombination, and boost carrier extraction. Notably, the GuABr-treated unencapsulated devices can still maintain more than 90 % of their initial PCE after aging for 1600 h at 16-25 °C and 35 %-50 % relative humidity in ambient conditions. This work reveals the significance of counterions in improving the photovoltaic performance and stability of PSCs.