NiN-Passivated NiO Hole-Transport Layer Improves Halide Perovskite-Based Solar Cell

Suppressing Redox Reactions at the Perovskite-Nickel Oxide Interface with Zinc Nitride to Improve the Performance of Perovskite Solar Cells

For p-i-n perovskite solar cells (PSCs), nickel oxide (NiOx) hole transport layers (HTLs) are the preferred interfacial layer due to their low cost, high mobility, high transmittance, and stability. However, the redox reaction between the Ni≥3+ and hydroxyl groups in the NiOx and perovskite layer leads to oxidized CH3NH3 + and reacts with PbI in the perovskite, resulting in a large number of non-radiative recombination sites. Among various transition metals, an ultra-thin zinc nitride (Zn3N2) layer on the NiOx surface is chosen to prevent these redox reactions and interfacial issues using a simple solution process at low temperatures. The redox reaction and non-radiative recombination at the interface of the perovskite and NiOx reduce chemically by using interface modifier Zn3N2 to reduce hydroxyl group and defects on the surface of NiOx. A thin layer of Zn3N2 at the NiOx/perovskite interface results in a high Ni3+/Ni2+ ratio and a significant work function (WF), which inhibits the redox reaction and provides a highly aligned energy level with perovskite crystal and rigorous trap-passivation ability. Consequently, Zn3N2-modified NiOx-based PSCs achieve a champion PCE of 21.61%, over the NiOx-based PSCs. After Zn3N2 modification, the PSC can improve stability under several conditions.

Evaporated Nickel Oxide Films with Slow Annealing and Interface Modification for Perovskite Solar Cells

Electron-beam-evaporated nickel oxide (NiOx) films are known for their high quality, precise control, and suitability for complex structures in perovskite (PVK) solar cells (PSCs). However, untreated NiOx films have inherent challenges, such as surface defects, relatively low intrinsic conductivity, and shallow valence band maximum, which seriously restrict the efficiency and stability of the devices. To address these challenges, we employ a dual coordination optimization strategy. The strategy includes low heating rate annealing of NiOx films and using an aminoguanidine nitrate spin coating process on the surfaces of NiOx films to strategically modify NiOx films itself and the interface of NiOx/PVK. Under the synergistic effect of this dual optimization method, the quality of the films is significantly improved and its p-type characteristics are enhanced. At the same time, the interface defects and energy level alignment of the films are effectively improved, and the charge extraction ability at the interface is improved. The combined treatment significantly improved the efficiency of inverted PSCs, from 17.85% to 20.31%, and enhanced device stability under various conditions. This innovative dual-coordinated optimization strategy provides a clear and effective framework for improving the performance of NiOx films and inverted PSCs.

Surface Modulation via Conjugated Bithiophene Ammonium Salt for Efficient Inverted Perovskite Solar Cells

The metal halide perovskite absorbers are prone to surface defects, which severely limit the power conversion efficiencies (PCEs) and the operational stability of the perovskite solar cells (PSCs). Herein, trace amounts of bithiophene propylammonium iodide (bi-TPAI) are applied to modulate the surface properties of the gas-quenched perovskite. It is found that the bi-TPAI surface treatment has negligible impact on the perovskite morphology, but it can induce a defect passivation effect and facilitate the charge carrier extraction, contributing to the gain in the open-circuit voltage (Voc) and fill factor. As a result, the PCE of the gas-quenched sputtered NiOx-based inverted PSCs is enhanced from the initial 20.0% to 22.0%. Most importantly, the bi-TPAI treatment can largely alleviate or even eliminate the burn-in process during the maximum power point tracking measurement, improving the operational stability of the devices.