Nickel Oxide Hole Transport Layers in Perovskite Solar Cells

Nickel oxide (NiOₓ) has emerged as a robust inorganic hole transport layer (HTL) in perovskite solar cells, offering favourable wide band gap, high hole mobility and excellent environmental stability. Employed in both p–i–n and n–i–p architectures, NiOₓ serves to extract holes efficiently from the perovskite absorber while blocking electrons, thereby reducing recombination losses and enhancing device lifetimes. Processing methods range from low-temperature solution deposition and spin coating to radio-frequency sputtering and thermal evaporation, with post-treatments such as plasma oxidation, doping with alkali or transition-metal cations and surface functionalisation further tuning electrical conductivity and energy-level alignment. Interface engineering—through buffer layers, organic passivation or lattice-strain relief—addresses defect states at the NiOₓ/perovskite junction, boosting open-circuit voltage and fill factor. Owing to its compatibility with large-area fabrication and potential for flexible substrates, NiOₓ HTLs represent a pivotal step towards scalable, stable and high-efficiency perovskite photovoltaics.

Research from Nature Portfolio

Recent studies have employed solution-processed crystalline NiO nanoparticles as hole-transport layers in planar perovskite devices, demonstrating enhanced energy-level alignment with the perovskite absorber, superior electron-blocking capability and negligible hysteresis. These cells achieved power conversion efficiencies around 15.4%, open-circuit voltages exceeding 1.04 V and markedly improved air stability compared with conventional polymeric HTLs. Concurrently, optimisation of rf-sputtered undoped NiO thin films has shown that deposition pressure and crystallinity govern the density of nickel vacancies and resulting hole concentration. By fine-tuning these sputtering conditions, devices reached short-circuit current densities near 20 mA cm⁻² and fill factors above 0.70, underscoring the critical role of optical transmittance, bandgap engineering and moderate conductivity in maximising device performance.

Nickel Oxide Hole Transport Layers in Perovskite Solar Cells publication trend

The graph below shows the total number of articles in nickel oxide hole transport layers in perovskite solar cells across all publications each year (not limited to Nature Index journals).

Technical terms

Hole transport layer (HTL): a semiconductor film that selectively conducts positive charge carriers (holes) from the light-absorbing perovskite to the anode while blocking electrons.

Perovskite: a class of crystalline materials with formula ABX₃, prized in solar cells for strong light absorption and efficient charge transport.

Power conversion efficiency (PCE): the percentage of incident solar energy converted into electrical energy by a photovoltaic device.

Planar p-i-n structure: a device architecture in which p-type, intrinsic and n-type layers are sequentially deposited to form a flat absorber junction without mesoporous scaffolds.

Energy-level alignment: the matching of electronic band edges between adjacent layers to facilitate efficient charge separation and minimise energy losses.

References

1. Solution-Processible Crystalline NiO Nanoparticles for High-Performance Planar Perovskite Photovoltaic Cells. Scientific Reports (2016).
2. Engineered optical and electrical performance of rf–sputtered undoped nickel oxide thin films for inverted perovskite solar cells. Scientific Reports (2018).
3. Inorganic hole transport layers in inverted perovskite solar cells: A review. Nano Select (2021).
4. Nickel Oxide for Perovskite Photovoltaic Cells. Advanced Photonics Research (2021).
5. NiO/Perovskite Heterojunction Contact Engineering for Highly Efficient and Stable Perovskite Solar Cells. Advanced Science (2020).
6. Progress, highlights and perspectives on NiO in perovskite photovoltaics. Chemical Science (2020).