Interface engineering with NiO nanocrystals for highly efficient and stable planar perovskite solar cells

Multifunctional Organic Molecule for Defect Passivation of Perovskite for High-Performance Indoor Solar Cells

Perovskite solar cells (PSCs) can utilize the residual photons from indoor light and continuously supplement the energy supply for low-power electron devices, thereby showing the great potential for sustainable energy ecosystems. However, the solution-processed perovskites suffer from serious defect stacking within crystal lattices, compromising the low-light efficiency and operational stability. In this study, we designed a multifunctional organometallic salt named sodium sulfanilate (4-ABS), containing both electron-donating amine and sulfonic acid groups to effectively passivate the positively-charged defects, like under-coordinated Pb ions and iodine vacancies. The strong chemical coordination of 4-ABS with the octahedra framework can further regulate the crystallization kinetics of perovskite, facilitating the enlarged crystal sizes with mitigated grain boundaries within films. The synergistic optimization effects on trap suppression and crystallization modulation upon 4-ABS addition can reduce energy loss and mitigate ionic migration under low-light conditions. As a result, the optimized device demonstrated an improved power conversion efficiency from 22.48% to 24.34% and achieved an impressive efficiency of 41.11% under 1000 lux weak light conditions. This research provides an effective defect modulation strategy for synergistically boosting the device efficiency under standard and weak light irradiations.

Unexpected Electronic Features of NiO Quantum Dots Produced by Femtosecond Pulsed Laser Ablation in Water

This study examines the effect of quantum confinement and surface orientations on the electronic properties of NiO quantum dots. It compares NiO nanocrystals produced via atmospheric-pressure microplasma and femtosecond laser (fs-laser) ablation in water, finding that both methods yield quantum-confined nanocrystals with a defined face-centered cubic lattice. Notably, fs-laser synthesis generates crystalline nanocrystals from both crystalline and amorphous targets. While the electronic properties, i.e., energy of the highest occupied molecular orbital and lowest unoccupied molecular orbital (LUMO), of microplasma-synthesized NiO nanocrystals are consistent with the literature, the electronic characteristics of NiO nanocrystals produced by a fs-laser, particularly the high-lying LUMO level, are unusual for NiO quantum dots. Supported by density functional theory calculations, we show that the observed level positions are related to the different polar and nonpolar faces of the nanocrystal surface.

Roles of Inorganic Oxide Based HTMs towards Highly Efficient and Long-Term Stable PSC-A Review

In just a few years, the efficiency of perovskite-based solar cells (PSCs) has risen to 25.8%, making them competitive with current commercial technology. Due to the inherent advantage of perovskite thin films that can be fabricated using simple solution techniques at low temperatures, PSCs are regarded as one of the most important low-cost and mass-production prospects. The lack of stability, on the other hand, is one of the major barriers to PSC commercialization. The goal of this review is to highlight the most important aspects of recent improvements in PSCs, such as structural modification and fabrication procedures, which have resulted in increased device stability. The role of different types of hole transport layers (HTL) and the evolution of inorganic HTL including their fabrication techniques have been reviewed in detail in this review. We eloquently emphasized the variables that are critical for the successful commercialization of perovskite devices in the final section. To enhance perovskite solar cell commercialization, we also aimed to obtain insight into the operational stability of PSCs, as well as practical information on how to increase their stability through rational materials and device fabrication.

Interface Modification with CuCrO2 Nanocrystals for Highly Efficient and Stable Planar Perovskite Solar Cells

The interfaces between the absorber and charge transport layers are shown to be critical for the performance of perovskite solar cells (PSCs). PSCs based on the Spiro-OMeTAD hole transport layers generally suffer from the problems of stability and reproducibility. Inorganic hole transport materials CuCrO₂ have good chemical stability and high hole mobility. Herein, we reported the preparation of the delafossite-type CuCrO₂ nanocrystals with a template-etching-calcination method and the incorporation of the as-obtained CuCrO₂ nanocrystals at the perovskite/Spiro-OMeTAD interfaces of planar PSCs to improve the device efficiency and stability. Compared with the traditional hydrothermal method, the template-etching-calcination method used less calcination time to prepare CuCrO₂ nanocrystals. After the CuCrO₂ interface modification, the efficiency of PSCs improved from 18.08% to 20.66%. Additionally, the CuCrO₂-modified PSCs showed good stability by retaining nearly 90% of the initial PCE after being stored in a drybox for 30 days. The template-etching-calcination strategy will pave a new approach for the synthesis of high-performance inorganic hole-transporting materials.

n-type absorber by Cd2+ doping achieves high-performance carbon-based CsPbIBr2 perovskite solar cells

High efficiency and stability have long been the key issues faced by perovskite solar cells (PSCs). It is found that the CsPbIBr₂ all-inorganic perovskite has a suitable band gap and satisfactory stability, so it has attracted much attention. However, the many defects in the CsPbIBr₂ film are one of the main problems hindering the improvement of power conversion efficiency (PCE) of the CsPbIBr₂ PSCs. The substitution of trace impurities is undoubtedly a simple, cost-effective and efficient strategy. In this work, an appropriate amount of Cd²⁺ (1.0% mol of Pb²⁺) is added into the CsPbIBr₂ precursor solution to fabricate high quality CsPbIBr₂ film with improved crystallinity, reduced trap density, suppressed photo-generated carrier recombination, displayed n-type doping and optimized energy level alignment. The corresponding carbon-based all-inorganic Cd²⁺-doped CsPbIBr₂ PSCs achieve a maximum PCE of 10.63% with a high open circuit voltage (V_OC) of 1.324 V, which are much higher than those of the control one with a PCE of 8.48% and an V_OC of 1.235 V. The unencapsulated device can still retain more than 92% of the initial PCE when stored at ambient atmosphere (25 °C, relative humidity about 30%) for 40 days.

Metal-Organic Framework Materials for Perovskite Solar Cells

Metal-organic frameworks (MOFs) and MOF-derived materials have been used for several applications, such as hydrogen storage and separation, catalysis, and drug delivery, owing to them having a significantly large surface area and open pore structure. In recent years, MOFs have also been applied to thin-film solar cells, and attractive results have been obtained. In perovskite solar cells (PSCs), the MOF materials are used in the form of an additive for electron and hole transport layers, interlayer, and hybrid perovskite/MOF. MOFs have the potential to be used as a material for obtaining PSCs with high efficiency and stability. In this study, we briefly explain the synthesis of MOFs and the performance of organic and dye-sensitized solar cells with MOFs. Furthermore, we provide a detailed overview on the performance of the most recently reported PSCs using MOFs.

Low-Temperature (<40 °C) Atmospheric-Pressure Dielectric-Barrier-Discharge-Jet Treatment on Nickel Oxide for p-i-n Structure Perovskite Solar Cells

A scan-mode low-temperature (<40 °C) atmospheric-pressure helium (He) dielectric-barrier discharge jet (DBDjet) is applied to treat nickel oxide (NiO) thin films for p-i-n perovskite solar cells (PSCs). Reactive plasma species help reduce the trap density, improve the transmittance and wettability, and deepen the valence band maximum (VBM) level. A NiO surface with the lower trap density surface of NiO allows better interfacial contact with the MAPbI3 layer and increases the carrier extraction capability. MAPbI3 can better crystallize on a more hydrophilic NiO surface, thereby suppressing charge recombination from the grain boundary and the interface. Further, the deeper VBM allows better band alignment and reduces the probability of nonradiative recombination. NiO treatment using He DBDjet with a scan rate of 0.3 cm/s can improve PSC efficiency from 13.63 to 14.88%.

Highly Efficient CsPbBr3 Planar Perovskite Solar Cells via Additive Engineering with NH4SCN

Improving stability is a major aspect for commercial application of perovskite solar cells (PSCs). The all-inorganic CsPbBr₃ perovskite material has been proven to have excellent stability. However, the CsPbBr₃ film has a small range of light absorption and serious charge recombination at the interface or inside the device, so the power conversion efficiency is still lower than that of the organic-inorganic hybrid one. Here, we successfully fabricate high-quality CsPbBr₃ films via additive engineering with NH₄SCN. By incorporating NH₄⁺ and pseudo-halide ion SCN^- into the precursor solution, a smooth and dense CsPbBr₃ film with good crystallinity and low trap state density can be obtained. At the same time, the results of a series of photoluminescence and electrochemical analyses including electrical impedance spectroscopy, space-charge limited current method, Mott-Schottky data, and so on reveal that the NH₄SCN additive can greatly reduce the trap state density of the CsPbBr₃ film and also effectively inhibit interface recombination and promote charge transport in the CsPbBr₃ planar PSC. Finally, the CsPbBr₃ planar PSC prepared with a molar ratio of 1.5% NH₄SCN achieves a champion efficiency of 8.47%, higher than that of the pure one (7.12%).

Light trapping structures and plasmons synergistically enhance the photovoltaic performance of full-spectrum solar cells

A full-spectrum solar cell exhibits potential as an effective strategy to enhance the absorption of incident solar light. To ensure the absorption capability of solar cells, trapping structures or plasmons have emerged as two main ways of utilizing the full spectrum of solar energy. First, recent progress in the full-spectrum solar cells based on NCs was reviewed from the aspects of trapping structures and plasmon design. Moreover, the effects of light trapping and surface plasmon resonance on light absorption and photoelectronic conversion were emphasized and discussed. Finally, the application prospect of their combination in the field of full-spectrum solar cells was examined. It was pointed out that the deep exploration of the physical mechanism of photoelectric conversion, controllable preparation of the interface and stability of composite structures will become the main directions of future research.

Microplasma-synthesized ultra-small NiO nanocrystals, a ubiquitous hole transport material

We report on a one-step hybrid atmospheric pressure plasma-liquid synthesis of ultra-small NiO nanocrystals (2 nm mean diameter), which exhibit strong quantum confinement. We show the versatility of the synthesis process and present the superior material characteristics of the nanocrystals (NCs). The band diagram of the NiO NCs, obtained experimentally, highlights ideal features for their implementation as a hole transport layer in a wide range of photovoltaic (PV) device architectures. As a proof of concept, we demonstrate the NiO NCs as a hole transport layer for three different PV device test architectures, which incorporate silicon quantum dots (Si-QDs), nitrogen-doped carbon quantum dots (N-CQDs) and perovskite as absorber layers. Our results clearly show ideal band alignment which could lead to improved carrier extraction into the metal contacts for all three solar cells. In addition, in the case of perovskite solar cells, the NiO NC hole transport layer acted as a protective layer preventing the degradation of halide perovskites from ambient moisture with a stable performance for >70 days. Our results also show unique characteristics that are highly suitable for future developments in all-inorganic 3^rd generation solar cells (e.g. based on quantum dots) where quantum confinement can be used effectively to tune the band diagram to fit the energy level alignment requirements of different solar cell architectures.

Perovskite/Hole Transport Layer Interface Improvement by Solvent Engineering of Spiro-OMeTAD Precursor Solution

Perovskite solar cells (PSCs) are one of the most promising emerging energy-conversion technologies because of their high power conversion efficiencies (PCEs) and potentially low fabrication cost. To improve PCE, it is necessary to develop PSCs with good interfacial engineering to reduce the trap states and carrier transport barriers present at the various interfaces of the PSCs' architecture. This work reports a facile method to improve the interface between the perovskite absorber layer and the hole transport layer (HTL) by adding a small amount of acetonitrile (ACN) in the Spiro-OMeTAD precursor solution. This small amount of ACN dissolves the surface of the perovskite layer, allowing the formation of an interdiffusion structure between perovskite and Spiro-OMeTAD layers. This modification allows for an improved electrical contact, enhanced collection of holes, and reduced recombination losses at the interface between the perovskite and Spiro-OMeTAD layers and, consequently, enhances the PCE. A maximum PCE of 19.7% with low hysteresis and a steady-state power conversion efficiency of 19.0% is obtained for optimized PSCs.

Toward Highly Reproducible, Efficient, and Stable Perovskite Solar Cells via Interface Engineering with CoO Nanoplates

It is well-known that solution-processed polycrystalline perovskite films show a high density of parasitic traps and the defects mainly exist at grain boundaries and surfaces of polycrystal perovskite films, which would limit potential device performance by triggering the undesired recombination and impair device long-term stability by accelerating the degradation of perovskite films. In this regard, defect passivation is highly desirable for achieving efficient and stable perovskite solar cells (PSCs). Here, we report the fabrication of highly reproducible, efficient, and stable PSCs via interface engineering with CoO nanoplates. When a suitable concentration of CoO nanoplates solution is spin-coated on perovskite film, a discontinuous CoO nanoplates modified layer is obtained, which is advantageous to achieving highly photovoltaic performance of the device because the uncovered perovskite crystalline grains can guarantee the unobstructed transport of holes from perovskite layers to hole transport layers. Furthermore, the hydrophobic oleylamine ligands capped CoO nanoplates are well filled in the boundaries of perovskite crystalline grains to effectively passivate the trap states, suppress dark recombination, and enhance moisture-resistance. These benefits are propitious to achieving a 20.72% champion efficiency and a 20.20% steady-state efficiency of the devices with good reproducibility and stability.

Functional Metal Oxides in Perovskite Solar Cells

As extremely important inorganic materials, metal oxides play an irreplaceable role in solid perovskite solar cells. In this review, the preparation methods of metal oxides, their effects on the perovskite optoelectronic devices incorporated with the energy level compatibility of perovskite materials are provided. Finally, the possible reactions between interfaces during growth progress as well as passivation mechanism of some metal oxides to perovskite materials are discussed. The physical, chemical, and electrical properties of functional metal oxides endow the enhancement of the efficiency and stability of perovskite photovoltaic devices.

Synergistic interface and compositional engineering of inverted perovskite solar cells enables highly efficient and stable photovoltaic devices

Recently, interface and compositional engineering have been effective approaches in the field of perovskite solar cells (PSCs). In this work, the surface of the nickel oxide layer and perovskite composition are modified by poly[(9,9-bis(30-((N,N-dimethyl)-N-ethylammonium)-propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] dibromide (PFN-P2) and deionized (DI) water, respectively, which result in a device with 20.5% efficiency and great stability.