Solution Synthesized p-Type Copper Gallium Oxide Nanoplates as Hole Transport Layer for Organic Photovoltaic Devices

In Situ Electrochemical Cobalt Doping in Perovskite-Structured Lanthanum Nickelate Thin Film Toward Energy Conversion Enhancement of Polymer Solar Cells

This study demonstrates that the electrochemical doping of lanthanum nickelate (LNO) with cobalt ions is a promising strategy for enhancing its physical and electrochemical properties, which are critical for energy storage and conversion devices. LNO emerges as a promising hole transport layer (HTL) in solar cells due to its stability, large band gap, and high transparency. Nevertheless, its low conductivity and improperly aligned band positions are persistent problems. Here, in a pioneering endeavor, Co-doped LNO thin films were synthesized electrochemically and applied as the HTL in polymer solar cells (PSCs). Characterization revealed the impact of Co doping on the electrochemical, structural, morphological, and optical properties of LNO thin films. Depending on the Co doping level, PSCs based on 10 mol % Co-doped LNO outperformed pure LNO, achieving a champion efficiency of 6.11% with enhanced short-circuit current density (12.84 mA cm-2), fill factor (68%), open-circuit voltage (0.70 V), and external quantum efficiency (82.6%). This enhancement resulted from decreased series resistance, refined surface morphology, minimized trap-assisted recombination, enhanced conductivity, increased charge carrier production, favorable energy level alignment, and improved current extraction facilitated by LNC0.10O HTL. Moreover, the unencapsulated PSC-LNC0.10O long-term stability notably improved and retained 86% of its initial PCE after 450 h storage in ambient air, 82% after being continuously heated to 85 °C for 300 h, and 80% after operating at maximum power point for 300 h. These findings offer a straightforward approach to enhancing PSC performance through Co doping of LNO, supported by density functional theory (DFT) calculations that validate the experimental results and confirm the improvement in optical properties and stability of PSCs as an HTL.

Cracked Film Lithography with CuGaOx Buffers for Bifacial CdTe Photovoltaics

Bifacial CdTe solar cells with greater power density than the monofacial baselines are demonstrated by using a CuGaO_x rear interface buffer that passivates while reducing sheet resistance and contact resistance. Inserting CuGaO_x between the CdTe and Au increases mean power density from 18.0 ± 0.5 to 19.8 ± 0.4 mW cm^-2 for one sun front illumination. However, coupling CuGaO_x with a transparent conductive oxide leads to an electrical barrier. Instead, CuGaO_x is integrated with cracked film lithography (CFL)-patterned metal grids. CFL grid wires are spaced narrowly enough (≈10 µm) to alleviate semiconductor resistance while retaining enough passivation and transmittance for a bifacial power gain: bifacial CuGaO_x /CFL grids generate 19.1 ± 0.6 mW cm^-2 for 1 sun front + 0.08 sun rear illumination and 20.0 ± 0.6 mW cm^-2 at 1 sun front + 0.52 sun rear-the highest reported power density at field albedo conditions for a scaled polycrystalline absorber.

Defining the Role of Cr3+ as a Reductant in the Hydrothermal Synthesis of CuCrO2 Delafossite

The synthesis of nanocrystalline, p-type delafossite metal oxides (CuMO₂) via hydrothermal methods has been explored for a variety of energy conversion and storage applications. However, isolation of the pure phase ternary product is challenging due to the facile growth of unwanted, binary byproducts (CuO, Cu₂O, and M₂O₃) which could ultimately influence the optoelectronic properties of the resulting nanocrystals. Here, we report on the optimized hydrothermal synthesis of CuCrO₂ nanocrystals to limit the production of such byproducts. This material possesses a wide band gap and high reported conductivity, making it attractive for applications as the hole transport layer in a variety of heterojunction solar cells. An important aspect of this work is the consideration of Cr³⁺ as the reductant used to reduce Cu²⁺ to Cu⁺. This was confirmed by detection and quantification of CrO₄^2- as a product of hydrothermal synthesis in addition to the fact that CuCrO₂ purity was maximized at a ratio of 4:3 Cr/Cu, consistent with the proposed stoichiometric reaction: 4Cr³⁺ + 3Cu²⁺ + 20 OH^- → 3CuCrO₂ + CrO₄^2- + 10 H₂O. Using a 4:3 ratio of Cr/Cu starting materials and allowing the synthesis to proceed for 60 h eliminates the presence of CuO beyond detection by powder X-ray diffraction (pXRD). Furthermore, washing the solid product in 0.5 M NH₄OH removes Cu₂O and Cr₂O₃ impurities, leaving behind the isolated CuCrO₂ product as confirmed using pXRD and inductively coupled plasma mass spectrometry.

Annealing Studies of Copper Indium Oxide (Cu2In2O5) Thin Films Prepared by RF Magnetron Sputtering

Copper indium oxide (Cu2In2O5) thin films were deposited by the RF magnetron sputtering technique using a Cu2O:In2O3 target. The films were deposited on glass and quartz substrates at room temperature. The films were subsequently annealed at temperatures ranging from 100 to 900 °C in an O2 atmosphere. The X-ray diffraction (XRD) analysis performed on the samples identified the presence of Cu2In2O5 phases along with CuInO2 or In2O3 for the films annealed above 500 °C. An increase in grain size was identified with the increase in annealing temperatures from the XRD analysis. The grain sizes were calculated to vary between 10 and 27 nm in films annealed between 500 and 900 °C. A morphological study performed using SEM further confirmed the crystallization and the grain growth with increasing annealing temperatures. All films displayed high optical transmission of more than 70% in the wavelength region of 500–800 nm. Optical studies carried out on the films indicated a small bandgap change in the range of 3.4–3.6 eV during annealing.

Optimized Stoichiometry for CuCrO2 Thin Films as Hole Transparent Layer in PBDD4T-2F:PC70BM Organic Solar Cells

The performance and stability in atmospheric conditions of organic photovoltaic devices can be improved by the integration of stable and efficient photoactive materials as substituent of the chemically unstable poly (3,4-ethylene dioxythiophene):polystyrene sulfonate (PEDOT:PSS), generally used as organic hole transport layer. Promising candidates are p-type transparent conductive oxides, which combine good optoelectronic and a higher mechanical and chemical stability than the organic counterpart. In this work, we synthesize Cu-rich CuCrO2 thin films by aerosol-assisted chemical vapour deposition as an efficient alternative to PEDOT:PSS. The effect of stoichiometry on the structural, electrical, and optical properties was analysed to find a good compromise between transparency, resistivity, and energy bands alignment, to maximize the photovoltaic performances., Average transmittance and bandgap are reduced when increasing the Cu content in these out of stoichiometry CuCrO2 films. The lowest electrical resistivity is found for samples synthesized from a solution composition in the 60-70% range. The optimal starting solution composition was found at 65% of Cu cationic ratio corresponding to a singular point in Hackee's figure of merit of 1 × 10-7 Ω-1. PBDD4T-2F:PC70BM organic solar cells were fabricated by integrating CuCrO2 films grown from a solution composition ranging between 40% to 100% of Cu as hole transport layers. The solar cells integrating a film grown with a Cu solution composition of 65% achieved a power conversion efficiency as high as 3.1%, representing the best trade-off of the optoelectronic properties among the studied candidates. Additionally, despite the efficiencies achieved from CuCrO2-based organic solar cells are still inferior to the PEDOT:PSS counterpart, we demonstrated a significant enhancement of the lifetime in atmospheric conditions of optimal oxides-based organic photovoltaic devices.

Properties of RF Magnetron-Sputtered Copper Gallium Oxide (CuGa2O4) Thin Films

Thin films of CuGa2O4 were deposited using an RF magnetron-sputtering technique for the first time. The sputtered CuGa2O4 thin films were post-deposition annealed at temperatures varying from 100 to 900 °C in a constant O2 ambience for 1.5 h. Structural and morphological studies were performed on the films using X-ray diffraction analysis (XRD) and a Field Emission Scanning Electron Microscope (FESEM). The presence of CuGa2O4 phases along with the CuO phases was confirmed from the XRD analysis. The minimum critical temperature required to promote the crystal growth in the films was identified to be 500 °C using XRD analysis. The FESEM images showed an increase in the grain size with an increase in the annealing temperature. The resistivity values of the films were calculated to range between 6.47 × 103 and 2.5 × 108 Ωcm. Optical studies were performed on all of the films using a UV-Vis spectrophotometer. The optical transmission in the 200–800 nm wavelength region was noted to decrease with an increase in the annealing temperature. The optical bandgap value was recorded to range between 3.59 and 4.5 eV and showed an increasing trend with an increase in the annealing temperature.

Hybrid 3D Nanostructure-Based Hole Transport Layer for Highly Efficient Inverted Perovskite Solar Cells

In this study, we demonstrate a new hybrid three-dimensional (3D) nanostructure system as an efficient hole transport layer (HTL) by a facile design of a low-temperature solution process. It is realized by integrating high-conductive chromium-doped CuGaO₂ nanoplates synthesized with choline chloride (denoted as Cr/CuGaO₂-CC) into ultrasmall NiO_x nanoparticles. First, we propose to incorporate a Cr-doped strategy under hydrothermal synthesis conditions together with controllable intermediates and surfactants' assistance to synthesize fine-sized Cr/CuGaO₂-CC nanoplates. Subsequently, these two-dimensional (2D) nanoplates serve as the expressway for improving hole transportation/extraction properties. Meanwhile, the ultrasmall-sized NiO_x nanoparticles are employed to modify the surface for achieving unique surface properties. The HTL formed from the designed hybrid 3D-nanostructured system exhibits the advantages of smooth and full-covered surface, remarkable charge collection efficiency, energy level alignment between the electrode and perovskite layer, and the promotion of perovskite crystal growth. Consequently, nearly 20% of power conversion efficiency with negligible hysteresis is achieved in inverted perovskite solar cells (PSCs). This work not only demonstrates the potential applications of a 3D-nanostructured Cr/CuGaO₂-CC/NiO_x hybrid HTL in PSCs but also provides a fundamental insight into the design of hybrid material systems by manipulating electric behavior and morphology structure for achieving high-performance photovoltaic devices.

Inverted Perovskite Photovoltaics Using Flame Spray Pyrolysis Solution Based CuAlO2/Cu-O Hole-Selective Contact

We present the functionalization process of a conductive and transparent CuAlO₂/Cu-O hole-transporting layer (HTL). The CuAlO₂/Cu-O powders were developed by flame spray pyrolysis and their stabilized dispersions were treated by sonication and centrifugation methods. We show that when the supernatant part of the treated CuAlO₂/Cu-O dispersions is used for the development of CuAlO₂/Cu-O HTLs the corresponding inverted perovskite-based solar cells show improved functionality and power conversion efficiency of up to 16.3% with negligible hysteresis effect.

Design of an Inorganic Mesoporous Hole-Transporting Layer for Highly Efficient and Stable Inverted Perovskite Solar Cells

The unstable feature of the widely employed organic hole-transporting materials (HTMs) (e.g., spiro-MeOTAD) significantly limits the practical application of perovskite solar cells (PSCs). Therefore, it is desirable to design new structured PSCs with stable HTMs presenting excellent carrier extraction and transfer properties. This work demonstrates a new inverted PSC configuration. The new PSC has a graded band alignment and bilayered inorganic HTMs (i.e., compact NiO_x and mesoporous CuGaO₂ ). In comparison with planar-structured PSCs, the mesoporous CuGaO₂ can effectively extract holes from perovskite due to the increased contact area of the perovskite/HTM. The graded energy alignment constructed in the ultrathin compact NiO_x , mesoporous CuGaO₂ , and perovskite can facilitate carrier transfer and depress charge recombination. As a result, the champion device based on the newly designed mesoscopic PSCs yields a stabilized efficiency of ≈20%, which is considered one of the best results for inverted PSCs with inorganic HTMs. Additionally, the unencapsulated PSC device retains more than 80% of its original efficiency when subjected to thermal aging at 85 °C for 1000 h in a nitrogen atmosphere, thus demonstrating superior thermal stability of the device. This study may pave a new avenue to rational design of highly efficient and stable PSCs.

Combustion Synthesis of p-Type Transparent Conducting CuCrO2+x and Cu:CrOx Thin Films at 180 °C

Low-temperature solution processing of p-type transparent conducting oxides (TCOs) will open up new opportunities for applications on flexible substrates that utilize low-cost, large-area manufacturing. Here, we report a facile solution synthesis method that produces two p-type TCO thin films: copper chromium oxide and copper-doped chromium oxide. Using combustion chemistry, both films are solution processed at 180 °C, which is lower than most recent efforts. While adopting the same precursor preparation and annealing temperature, we find that annealing environment (solvent vapor vs open air) dictates the resulting film phase, hence the optoelectronic properties. The effect of annealing environment on the reaction mechanism is discussed. We further characterize the electronic, optical, and transport properties of the two materials, and compare the differences. Their applications in optoelectronic devices are successfully demonstrated in transparent p-n junction diodes and as hole transport layers in organic photovoltaic devices.

CuGaO2 : A Promising Inorganic Hole-Transporting Material for Highly Efficient and Stable Perovskite Solar Cells

The p-type inorganic semiconductor CuGaO₂ as a hole-transporting layer (HTL) in perovskite solar cells (PSCs) provides higher carrier mobility, better-energy level matching, and superior stability, as well as low-temperature processing technique. Compared to organic HTL, a very competitive PCE of 18.51% with long-term stability is achieved. This indicates that CuGaO₂ is a promising HTL for efficient and stable PSCs.

Photoluminescence and photocatalytic properties of rhombohedral CuGaO2 nanoplates

Rhombohedral phase CuGaO₂ nanoplates with a diameter of about 10 μm were synthesized via low temperature hydrothermal method. Room temperature and low temperature photoluminescence of the obtained CuGaO₂ nanoplates were characterized. CuGaO₂ nanoplates exhibited blue emission at room temperature and free exciton emission were appeared at low temperature. The blue emission is originated from defects such as Cu vacancies, which is the possible origin of p-type conductivity. The appearance of free exciton emission can demonstrate the direct bandgap transition behavior of CuGaO₂ nanoplates. The as-prepared p-type CuGaO₂ nanoplates were further decorated by n-type ZnO nanoparticles via calcination method to fabricate p-n junction nanocomposites. The nanocomposites exhibited enhanced photocatalytic activity which can be ascribed to the effective separation of photogenerated carriers by the internal electrostatic field in the p-n junction region, and the enhanced light absorption properties resulted from sub-bandgap absorption effect of p-n junction. This work has offered a new insight into the design of p-n junction devices using p-type CuGaO₂ nanoplates.

Effects of Contact-Induced Doping on the Behaviors of Organic Photovoltaic Devices

Substrates can significantly affect the electronic properties of organic semiconductors. In this paper, we report the effects of contact-induced doping, arising from charge transfer between a high work function hole extraction layer (HEL) and the organic active layer, on organic photovoltaic device performance. Employing a high work function HEL is found to increase doping in the active layer and decrease photocurrent. Combined experimental and modeling investigations reveal that higher doping increases polaron-exciton quenching and carrier recombination within the field-free region. Consequently, there exists an optimal HEL work function that enables a large built-in field while keeping the active layer doping low. This value is found to be ~0.4 eV larger than the pinning level of the active layer material. These understandings establish a criterion for optimal design of the HEL when adapting a new active layer system and can shed light on optimizing performance in other organic electronic devices.

Delafossite Nanoparticle as New Functional Materials: Advances in Energy, Nanomedicine and Environmental Applications

Recently, numerous delafossite oxides in nanoscale have been reported for diverse applications. The present review summarized the recent overall views of delafossite nanoparticles in diverse applications such as energy, catalysis, photocatalysis, nanomedicine, sensors, electrochemical devices and environmental concerns. Delafossite nanoparticles possess unique features such as different and wide chemical composition, large surface area, small energy gap, ability for further functionalization, possess dual-active sites with different oxidation states (A+and M3+), and eager for doping with various species with feasibility to undergo structure modification. Thus, they provided promising application such as solar cell, photocatalysis, hydrogen production, bioactive materials, separation purposes and others. Pros, cons, current and future status were also reviewed.