NiOx-based Perovskite Solar Cells Research Articles

Solvent management and Li+/Mg2+ co-doping enable efficient n-i-p NiOx-based perovskite solar cells

Spin-coating pre-fabricated NiOx nanocrystals using an annealing-free process is a compatible technique for fabricating the hole transport layer in n-i-p structured perovskite solar cells. The solvothermal method, assisted by long-chain fatty acids or amines such as oleic acid and oleylamine, has demonstrated the applicability of fabricating NiOx nanoparticles with uniform morphology and size. However, the long-chain fatty acids or amines covering the NiOx nanoparticles cannot be removed at low temperature, obstructing the transport of photo-generated holes due to their insulating characteristics. Herein, triphenylphosphine is employed to replace a portion of oleylamine in the solvothermal reaction solution. Experimental results demonstrate that the introduction of triphenylphosphine does not affect the dispersion of the synthesized NiOx nanoparticles in toluene. The as-fabricated n-i-p structured device receives an efficiency of 12.63 %. Thereafter, Li+ doping and Li+-Mg2+ co-doping strategies are used to further enhance the devices' performance. The best-behaved device with Li+-Mg2+ co-doping NiOx hole transport layer acquires an efficiency of 16.20 %. This research provides a practical approach for fabricating efficient NiOx hole transport materials for n-i-p structured perovskite solar cells.

Bilateral Chemical Linking at NiOx Buried Interface Enables Efficient and Stable Inverted Perovskite Solar Cells and Modules.

Inverted NiOx-based perovskite solar cells (PSCs) exhibit considerable potential because of their low-temperature processing and outstanding excellent stability, while is challenged by the carriers transfer at buried interface owing to the inherent low carrier mobility and abundant surface defects that directly deteriorates the overall device fill factor. Present work demonstrates a chemical linker with the capability of simultaneously grasping NiOx and perovskite crystals by forming a Ni-S-Pb bridge at buried interface to significantly boost the carriers transfer, based on a rationally selected molecule of 1,3-dimethyl-benzoimidazol-2-thione (NCS). The constructed buried interface not only reduces the pinholes and needle-like residual PbI2 at the buried interface, but also deepens the work function and valence band maximum positions of NiOx, resulting in a smaller VBM offset between NiOx and perovskite film. Consequently, the modulated PSCs achieved a high fill factor up to 86.24 %, which is as far as we know the highest value in records of NiOx-based inverted PSCs. The NCS custom-tailored PSCs and minimodules (active area of 18 cm2) exhibited a champion efficiency of 25.05 % and 21.16 %, respectively. The unencapsulated devices remains over 90 % of their initial efficiency at maximum power point under continuous illumination for 1700 hours.

Interface Defects Dependent on Perovskite Annealing Temperature for NiOX-Based Inverted CsPbI2Br Perovskite Solar Cells.

Nickel oxide (NiOX) is an ideal inorganic hole transport material for the fabrication of inverted perovskite solar cells owing to its excellent optical and semiconductor properties. Currently, the main research on developing the performance of NiOX-based perovskite solar cells focuses on improving the conductivity of NiOX thin films and preventing the redox reactions between metal cations (Ni3+ on the surface of NiOX) and organic cations (FA+ or MA+ in the perovskite precursors) at the NiOX/perovskite interface. In this study, a new type of interface defects in NiOX-based CsPbI2Br solar cells is reported. That is the Pb2+ from CsPbI2Br perovskites can diffuse into the lattice of NiOX surface as the annealing temperature of perovskites changes. The diffusion of Pb2+ increases the ratio of Ni3+/Ni2+ on the surface of NiOX, leading to an increase in the density of trap state at the interface between NiOX and perovskites, which eventually results in a serious decline in the photovoltaic performance of solar cells.

Spontaneous decoration of ionic compounds at perovskite interfaces to achieve 23.38% efficiency with 85% fill factor in NiOX-based perovskite solar cells

Inorganic hole transport materials, particularly NiOX, have shown considerable promise in boosting the efficiency and stability of perovskite solar cells. However, a major barrier to commercialization of NiOX-based perovskite solar cells with positive-intrinsic-negative architectures is their direct contact with the absorbing layer, which can lead to losses of photovoltage and fill factor. Furthermore, highly positive under-coordinated Ni cations degrade the perovskite at the interface. Here, we address these issues with the use of an ionic compound (QAPyBF4) as an additive to passivate defects throughout the perovskite layer and improve carrier conduction and interactions with under-coordinated Ni cations. Specifically, the highly electronegative inorganic anion [BF4]− interacts with the NiOx/perovskite interface to passivate under-coordinated cations (Ni≥3+). Accordingly, the decorated cells achieved a power conversion efficiency of 23.38% and a fill factor of 85.5% without a complex surface treatment or NiOX doping.

Multi-functional buried interface engineering derived from in-situ-formed 2D perovskites using π-conjugated liquid-crystalline molecule with aggregation-induced emission for efficient and stable NiOx-based inverted perovskite solar cells

The poor and limited-functional NiOx/perovskite buried interface has hindered the development of NiOx-based perovskite solar cells (PSCs). Herein, a π-conjugated liquid-crystalline organic spacer with aggregation-induced emission (AIE), (Z)-2-([1,1′-biphenyl]-4-yl)-3-(4-(3-aminopropoxy)phenyl)acrylonitrile (BPCSA), is employed for the multi-functional NiOx/perovskite buried interface engineering. The functional groups of BPCSA spacer can coordinate with NiOx and induce the in-situ formation of 2D perovskite at the NiOx/perovskite interface. The in-situ-formed 2D perovskite interlayer can passivate interface defects, strengthen interface interconnection and optimize energy level alignment between NiOx and 3D perovskites. More markedly, the π-conjugated liquid-crystalline molecular structure and AIE property of BPCSA spacer can guide the high-quality crystal growth of upper 3D perovskite films, release interfacial strain, facilitate interfacial carrier transport and realize efficient photosensitization process concurrently. Consequently, such 3D/2D PSCs can acquire a champion power conversion efficiency (PCE) of 23.45% with improved stability. Besides, high-performance flexible 3D/2D PSCs are also successfully demonstrated.

Construction of Charge Transport Channels at the NiOx/Perovskite Interface through Moderate Dipoles toward Highly Efficient Inverted Solar Cells.

NiOx-based perovskite solar cells (PSCs) have attracted much attention because of their low fabrication temperature, suppressed hysteresis, and superior stability. However, the poor interfacial contacts between NiOx and perovskite layers always limit the progress of PSCs. Here, we applied 2-thiophenemethylamine (TPMA) as charge transport channels at the interface between NiOx and perovskite layers. The introduction of TPMA provides moderate dipole moment pointing to the perovskite side and effectively promotes the charge transportation. Meanwhile, TPMA anchorage also passivates the defect states at the surfaces of both NiOx and MAPbI3, which compensates the voltage loss due to the change in NiOx work function induced by the dipole. Thus, the device performance has been significantly enhanced in both electrochemical properties and power conversion efficiency. Our work has demonstrated a new way of improving current and voltage in the NiOx-based PSCs simultaneously through a moderate interfacial dipole moment toward highly efficient PSCs.

Obstructing interfacial reaction between NiOx and perovskite to enable efficient and stable inverted perovskite solar cells

In NiOx-based perovskite solar cells (PVSCs), the interfacial redox reaction between Ni3+ (on the surface of NiOx) and A-site cation salt (MAI in perovskite precursor solution) is invariably ignored. This adverse reaction will generate PbI2-rich hole extraction barriers at the NiOx-perovskite interface, which limits hole transmission and increases charge recombination, thus resulting in open-circuit voltage (Voc) loss. Furthermore, it will accelerate perovskite degradation by deprotonating the precursor amine and oxidizing iodide to interstitial iodine, which induces the severe instability of devices. Herein, a physical separation strategy by introducing a modifier layer to obstruct the detrimental reaction is explored. The results demonstrate that the trimethylolpropane tris(2-methyl-1-aziridinepropionate) (SaC-100) depositing onto NiOx can suppress the reaction between Ni3+ and MAI to endow the improvement of conductivity and reduction of interfacial defects, thus reducing Voc loss and enhancing device stability. Moreover, the interfacial energy level alignment and the morphology of perovskite are also optimized. As a result, the PVSCs device based on NiOx/SaC-100 presents the best power conversion efficiency (PCE) of 20.21% with a superior Voc value of 1.12 V. Furthermore, the device shows better light and thermal stability because of the hindering effect and defect passivation effect of SaC-100.

Enhanced Efficiency and Stability of NiOx-Based Perovskite Solar Cells Using [6,6]-Phenyl-C61-butyric Acid Methyl-Doped Poly(9-vinylcarbazole)-Modified Layer

In recent years, the power conversion efficiency (PCE) of NiOx-based perovskite solar cells (PSCs) has increased by leaps and bounds, reaching more than 20%. However, the structure of PSCs is unsta...

Two-step annealing of NiOx enhances the NiOx–perovskite interface for high-performance ambient-stable p–i–n perovskite solar cells

In this study, we applied two-step annealing to nickel oxide (NiOx) films that we then used in perovskite solar cells (PSCs). The optimized annealing process resulted in a change in the structure and chemical composition of the NiOx, leading to a change in the work function and improved conductivity for NiOx-coated ITO substrates. X-ray photoelectron spectroscopy suggested that a change in the Ni2+/Ni3+ ratio of NiO (Ni 2p at 854.0 eV) and the presence of Ni3+ species induced by vacancies in Ni2O3 (Ni 2p at 855.6 eV) and NiOOH (Ni 2p at 856.7 eV) were responsible for the enhanced conductivity of the two-step-annealed NiOx films. The modified NiOx served as an efficient hole transporting layer, enhancing the PL quenching behavior at the perovskite–NiOx interface. Time-resolved photoluminescence measurements provided evidence for efficient carrier extraction. These improvements led to increases in the fill factors and power conversion efficiencies (PCEs) of corresponding PSC devices. The champion device displayed a PCE of 19.04%—a value comparable with those of state-of-the-art NiOx-based PSCs. Furthermore, the devices possessed excellent air-stability, retaining 97% of their PCEs after storage in air for over 672 h (at 25 °C, with a humidity of 40%).

Pyridine-Terminated Conjugated Organic Molecules as an Interfacial Hole Transfer Bridge for NiOx-Based Perovskite Solar Cells.

To engineer the NiOx/perovskite interface and promote interfacial hole transfer, two pyridine-terminated conjugated small organic molecules (PTZ-1 and PTZ-2) are synthesized to link the NiOx and perovskite layers for NiOx-based perovskite solar cells (PSCs). One terminal pyridine group interacts with the NiOx layer, while the other one coordinates with the Pb atoms of the perovskite layer, erecting an interfacial hole transfer bridge between NiOx and perovskite. Surface modification of the NiOx film with the PTZ molecules is able to enhance hole extraction, increase hole mobility and conductivity of NiOx, reduce defect density, and retard interfacial charge recombination. As a consequence, power conversion efficiency is improved from 12.53 to 16.25 and 17.00% upon surface modifications of NiOx with PTZ-1 and PTZ-2, respectively. Furthermore, the modified PSCs exhibit almost no hysteresis and show good stability after storage in air (relative humidity of 30-40%) for 500 h without encapsulation.

An efficient and simple dual effect by under-layer abduction design for highly flexible NiOx-based perovskite solar cells

Organic-inorganic hybrid perovskite with large crystal size and high quality are desirable for making high-performance solar cell. However, the expectant film with good surface is normally limited by various factors, such as under-layer, film thickness. Here, an efficient dual effect method on the performance by means of under-layer abduction strategy is developed to improve perovskite crystallization by incorporating nitrogen-doped reduced graphene oxide into nickel oxide as hole transport layer, which significantly improves the electrical conductivity, and endows composite material with encouraging hydrophobic property. In addition, the modified under-layer enhances the space of crystal nucleation and facilitates crystal growth through grain boundary migration, thereby achieving large crystal size and reduced grain boundaries. Consequently, a best device with maximum power conversion efficiency of 18.84% is achieved due to a significant improvement in fill factor and short-circuit current density. Moreover, its flexible application shows an efficiency of 14.11%, retaining >90% after aging for 1200 h without encapsulation. This work provides a potential platform to fabricate low cost and efficient hole extraction materials for large scale and flexible perovskite solar cell.

Enhanced efficiency and air-stability of NiOX-based perovskite solar cells via PCBM electron transport layer modification with Triton X-100.

We modified phenyl-C61-butyric acid methyl ester (PCBM) for use as a stable, efficient electron transport layer (ETL) in inverted perovskite solar cells (PSCs). PCBM containing a surfactant Triton X-100 acts as the ETL and NiOX nanocrystals act as a hole transport layer (HTL). Atomic force microscopy and scanning electron microscopy images showed that surfactant-modified PCBM (s-PCBM) forms a high-quality, uniform, and dense ETL on the rough perovskite layer. This layer effectively blocks holes and reduces interfacial recombination. Steady-state photoluminescence and electrochemical impedance spectroscopy analyses confirmed that Triton X-100 improved the electron extraction performance of PCBM. When the s-PCBM ETL was used, the average power conversion efficiency increased from 10.76% to 15.68%. This improvement was primarily caused by the increases in the open-circuit voltage and fill factor. s-PCBM-based PSCs also showed good air-stability, retaining 83.8% of their initial performance after 800 h under ambient conditions.