Metal Oxide Charge Transport Layers for Efficient and Stable Perovskite Solar Cells

Currently, the efficiency of perovskite solar cells (PSCs) is ≈24%. For the fabrication of such high efficiency PSCs, it is necessary to use both electron and hole transport layers to effectively separate the charges generated by light absorption of the perovskite layer and selectively transfer the separated electrons and holes. In addition to the efficiency, the materials used for transporting charges must be resilient to light, heat, and moisture to ensure long‐term stability of PSCs; furthermore, low‐cost fabrication is required to form a charge transport layer at low temperatures by a solution process. For this purpose, metal oxides are best suited as charge transport materials for PSCs because of their advantages such as low cost, long‐term stability, and high efficiency. In this Review, the metal oxide electron and hole transport materials used in PSCs are reviewed and preparation of these materials is summarized. Finally, the challenges and future research direction for metal oxide‐based charge transport materials are described.     

Functionalization of Graphene Oxide Films with Au and MoOx Nanoparticles as Efficient p‐Contact Electrodes for Inverted Planar Perovskite Solar Cells

A graphene oxide (GO) film is functionalized with metal (Au) and metal‐oxide (MoO_x) nanoparticles (NPs) as a hole‐extraction layer for high‐performance inverted planar‐heterojunction perovskite solar cells (PSCs). These NPs can increase the work function of GO, which is confirmed with X‐ray photoelectron spectra, Kelvin probe force microscopy, and ultraviolet photoelectron spectra measurements. The down‐shifts of work functions lead to a decreased level of potential energy and hence increased V_oc of the PSC devices. Although the GO‐AuNP film shows rapid hole extraction and increased V_oc, a J_sc improvement is not observed because of localization of the extracted holes inside the AuNP that leads to rapid charge recombination, which is confirmed with transient photoelectric measurements. The power conversion efficiency (PCE) of the GO‐AuNP device attains 14.6%, which is comparable with that of the GO‐based device (14.4%). In contrast, the rapid hole extraction from perovskite to the GO‐MoO_x layer does not cause trapping of holes and delocalization of holes in the GO film accelerates rapid charge transfer to the indium tin oxide substrate; charge recombination in the perovskite/GO‐MoO_x interface is hence significantly retarded. The GO‐MoO_x device consequently shows significantly enhanced V_oc and J_sc, for which its device performance attains PCE of 16.7% with great reproducibility and enduring stability.     

Solution‐Processed Metal Oxide Nanocrystals as Carrier Transport Layers in Organic and Perovskite Solar Cells

There has been rapid progress in solution‐processed organic solar cells (OSCs) and perovskite solar cells (PVSCs) toward low‐cost and high‐throughput photovoltaic technology. Carrier (electron and hole) transport layers (CTLs) play a critical role in boosting their efficiency and long‐time stability. Solution‐processed metal oxide nanocrystals (SMONCs) as a promising CTL candidate, featuring robust process conditions, low‐cost, tunable optoelectronic properties, and intrinsic stability, offer unique advantages for realizing cost‐effective, high‐performance, large‐area, and mechanically flexible photovoltaic devices. In this review, the recent development of SMONC‐based CTLs in OSCs and PVSCs is summarized. This paper starts with the discussion of synthesis approaches of SMONCs. Then, a broad range of SMONC‐based CTLs, including hole transport layers and electron transport layers, are reviewed, in which an emphasis is placed on the improvement of the efficiency and device stability. Finally, for the better understanding of the challenges and opportunities on SMONC‐based CTLs, several strategies and perspectives are outlined.     

A Terminally Tetrafluorinated Nonfullerene Acceptor for Well‐Performing Alloy Ternary Solar Cells

Fabricating ternary solar cells is a pivotal strategy to improve the power conversion efficiencies (PCEs) of organic photovoltaic devices. However, it is still a challenge to simultaneously improve the performance parameters of ternary devices. Therefore, the third ingredient in ternary blends should be precisely designed or selected. Herein, a new medium‐bandgap small‐molecule acceptor, namely, 3,9‐bis(2‐methylene‐(3‐(1‐(3,5‐dimethylphenyl)‐1cyanomethylene)indanone))‐5,5,11,11‐tetrakis‐(4‐hexylphenyl)dithieno[2,3‐d:2′,3′‐d′]‐sindaceno[1,2‐b:5,6‐b′]dithiophene (ITIF), is synthesized by end‐capping with a new fluorinated, asymmetric terminal group, (Z)‐2‐(3,5‐difluorophenyl)‐2‐(3‐oxo‐2,3‐dihydro‐1H‐inden‐1‐ylidene) acetonitrile. Replacing the CN substituent with the asymmetric 3,5‐difluorophenyl substituent obviously up‐shifts the lowest unoccupied molecular orbital (LUMO) level of ITIF to ?3.78 eV, enlarges the bandgap to 1.82 eV, and improves the absorption coefficient to ≈50% higher than that of 3,9‐bis(2‐methylene‐(3‐(1,1‐dicyanomethylene)indanone))‐5,5,11,11‐tetrakis‐(4‐hexylphenyl)dithieno[2,3‐d:2′,3′‐d′]‐sindaceno[1,2‐b:5,6‐b′]dithiophene (ITIC). Due to the similar structures, ITIF and ITIC can combine as an alloyed acceptor, which makes it convenient to tune the morphology and optical and electrochemical properties of ternary blends. The enhanced absorption coefficient of ITIF and the rapid fluorescence resonance energy transfer from ITIF to ITIC remarkably improve the absorption of the ternary blend film, hence compensating for the external quantum efficiency (EQE) curves. When ITIF is introduced into ternary solar cells based on poly[(2,6‐(4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)‐benzo[1,2‐b:4,5‐b′]dithiophene))‐alt‐(5,5‐(1′,3′‐di‐2‐thienyl‐5′,7′‐bis(2‐ethylhexyl)benzo[1′,2′‐c:4′,5′‐c′]dithiophene‐4,8‐dione)] (PBDB‐T):ITIF:ITIC blends, the PCEs of the ternary devices are increased from 9.2% to 10.5%, and the short‐circuit currents, open‐circuit voltages, and fill factors are simultaneously improved.     

Oxide Sandwiched Metal Thin‐Film Electrodes for Long‐Term Stable Organic Solar Cells

Oxide/silver/oxide multilayers as semitransparent top electrode for small molecule organic solar cells (OSCs) are presented. It is shown that two oxide layers sandwiching a central metal layer greatly improve the stability and lifetime of the organic solar cell. Thermally evaporated MoO₃, WO₃, or V₂O₅ layers are employed as an interlayer for subsequent silver deposition and significantly change the morphology of the ultrathin silver layer, improving charge extraction and electrodes series resistance. The transmittance of the electrode is increased by introducing oxide or oxide and organic multilayers as capping layer, which leads to higher photocurrent generation in the absorber layer. Application of 1 nm MoO₃/11 nm Ag/10 nm MoO₃/50 nm Alq₃ multilayer electrodes in OSCs lead to an efficiency of 2.6% for a standard ZnPc:C60 cell, showing superior performance compared to devices with pure silver top contacts. The device lifetime is also strongly increased. MoO₃ layers can saturate and stabilize the inner and outer metal surface, passivating it against most of the degradation mechanisms. With such an oxide/silver/oxide multilayer electrode, the time until the glass encapsulated OSC is degraded to 80% of its starting efficiency is enhanced from 86 h to approximately 4500 h compared to an OSC without an oxide interlayer.     

Overcoming Zinc Oxide Interface Instability with a Methylammonium‐Free Perovskite for High‐Performance Solar Cells

Perovskite solar cells have achieved the highest power conversion efficiencies on metal oxide n‐type layers, including SnO₂ and TiO₂. Despite ZnO having superior optoelectronic properties to these metal oxides, such as improved transmittance, higher conductivity, and closer conduction band alignment to methylammonium (MA)PbI₃, ZnO is largely overlooked due to a chemical instability when in contact with metal halide perovskites, which leads to rapid decomposition of the perovskite. While surface passivation techniques have somewhat mitigated this instability, investigations as to whether all metal halide perovskites exhibit this instability with ZnO are yet to be undertaken. Experimental methods to elucidate the degradation mechanisms at ZnO–MAPbI₃ interfaces are developed. By substituting MA with formamidinium (FA) and cesium (Cs), the stability of the perovskite–ZnO interface is greatly enhanced and it is found that stability compares favorably with SnO₂‐based devices after high‐intensity UV irradiation and 85 °C thermal stressing. For devices comprising FA‐ and Cs‐based metal halide perovskite absorber layers on ZnO, a 21.1% scanned power conversion efficiency and 18% steady‐state power output are achieved. This work demonstrates that ZnO appears to be as feasible an n‐type charge extraction layer as SnO₂, with many foreseeable advantages, provided that MA cations are avoided.     

Printable and Large‐Area Organic Solar Cells Enabled by a Ternary Pseudo‐Planar Heterojunction Strategy

Bulk heterojunction (BHJ) processing technology has had an irreplaceable role in the development of organic solar cells (OSCs) in the past decades due to the significant advantages in achieving high‐power conversion efficiency (PCE). However, the difficulty in exploring and regulating morphology makes it inadequate for upscaling large‐area OSCs. In this work, printable high‐performance ternary devices are fabricated by a pseudo‐planar heterojunction (PPHJ) strategy. The fullerene derivative indene‐C₆₀ bisadduct (ICBA) is incorporated into PM6/IT‐4F system to expand the vertical phase separation and facilitate an obvious PPHJ structure. After the addition of ICBA, the IT‐4F enriches on the surface of active layer, while PM6 is accumulated underneath. Furthermore, it increases the crystallinity of PM6, which facilitates exciton dissociation and charge transfer. Accordingly, 1.05 cm² devices are fabricated by blade‐coating with an enhanced PCE of 14.25% as compared to the BHJ devices (13.73%). The ternary PPHJ strategy provides an effective way to optimize the vertical phase separation of organic semiconductor during scalable printing methods.     

A Solution‐Processed MoOx Anode Interlayer for Use within Organic Photovoltaic Devices

A simple, solution‐processed route to the development of MoO_x thin‐films using oxomolybdate precursors is presented. The chemical, structural, and electronic properties of these species are characterized in detail, within solution and thin‐films, using electrospray ionization mass spectrometry, grazing angle Fourier transform infrared spectroscopy, thermogravimetric analysis, atomic force microscopy, X‐ray photoelectron spectroscopy, and ultraviolet photoelectron spectroscopy. These analyses show that under suitable deposition conditions the resulting solution processed MoO_x thin‐films possess the appropriate morphological and electronic properties to be suitable for use in organic electronics. This is exemplified through the fabrication of poly(3‐hexylthiophene):[6,6]‐phenyl C₆₁ butyric acid methyl ester (P3HT:PC₆₁BM) bulk heterojunction (BHJ) solar cells and comparisons to the traditionally used poly(3,4‐ethyldioxythiophene)/poly(styrenesulfonate) anode modifying layer.     

A General and Efficient Route to Fabricate Carbon Nanotube‐Metal Nanoparticles and Carbon Nanotube‐Inorganic Oxides Hybrids

Novel pyrenyl‐moieties‐decorated hyperbranched polyglycidol (pHBP) is synthesized and utilized for the functionalization of carbon nanotubes (CNTs) via a non‐covalent (non‐destructive) process. Mediated by a pHBP layer on the CNT sidewall, Au, Ag and Pt nanoparticles and uniform SiO₂, GeO₂ and TiO₂ coatings are generated in situ and deposited onto the as‐prepared CNT/pHBP hybrids, forming versatile homogeneous CNT‐based nanohybrid sols. The coverage of metal nanoparticles and oxide coatings is controllable simply by changing the employed amount of precursors. This easy synthetic strategy provides a general and convenient route to efficiently assemble a wide range of metal nanoparticles and inorganic oxide components on the sidewalls of CNTs, and enables the construction of heterogeneous nanostructures with novel functionalities. As a means of demonstrating the versatility of the fabricated hybrid materials, the catalytic function of CNT/pHBP/Pt hybrids towards the reduction of 4‐nitrophenol and the incorporation of dye molecules into the CNT/pHBP/SiO₂ matrix resulting in fluorescent nanofibers are investigated.     

Polydisperse Aggregates of ZnO Nanocrystallites: A Method for Energy‐Conversion‐Efficiency Enhancement in Dye‐Sensitized Solar Cells

ZnO films consisting of either polydisperse or monodisperse aggregates of nanocrystallites were fabricated and studied as dye‐sensitized solar‐cell electrodes. The results revealed that the overall energy‐conversion efficiency of the cells could be significantly affected by either the average size or the size distribution of the ZnO aggregates. The highest overall energy‐conversion efficiency of ～4.4% was achieved with the film formed by polydisperse ZnO aggregates with a broad size distribution from 120 to 360 nm in diameter. Light scattering by the submicrometer‐sized ZnO aggregates was employed to explain the improved solar‐cell performance through extending the distance travelled by light so as to increase the light‐harvesting efficiency of photoelectrode film. The broad distribution of aggregate size provides the ZnO films with both better packing and an enhanced ability to scatter the incident light, and thus promotes the solar‐cell performance.     

A Graphene Oxide and Copper‐Centered Metal Organic Framework Composite as a Tri‐Functional Catalyst for HER,OER, and ORR

A composite made from the assembly of graphene oxide (GO) and copper‐centered metal organic framework (MOF) shows good performance as a tri‐functional catalyst in three important electrocatalysis reactions, namely: the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR). One of the challenges in the area of electrocatalysis is to find an effective catalyst that will reduce, as well as generate, oxygen at moderate temperatures. The enhanced electrocatalytic properties and stability in acid of the GO‐MOF composite is due to the unqiue porous scaffold structure, improved charge transport and synergistic interactions between the GO and MOF. In polymer electrolyte membrane fuel cell testing, the GO‐incorporated Cu‐MOF composite delivers a power density that is 76% that of the commercial Pt catalyst.     

Carbon Nanotubes Rooted in Porous Ternary Metal Sulfide@N/S‐Doped Carbon Dodecahedron: Bimetal‐Organic‐Frameworks Derivation and Electrochemical Application for High‐Capacity and Long‐Life Lithium‐Ion Batteries

Lithium ion battery is the predominant power source for portable electronic devices, electrical vehicles, and back‐up electricity storage units for clean and renewable energies. High‐capacity and long‐life electrode materials are essential for the next‐generation Li‐ion battery with high energy density. Here bimetal‐organic‐frameworks synthesis of Co_0.4Zn_0.19S@N and S codoped carbon dodecahedron is shown with rooted carbon nanotubes (Co‐Zn‐S@N‐S‐C‐CNT) for high‐performance Li‐ion battery application. Benefiting from the synergetic effect of two metal sulfide species for Li‐storage at different voltages, mesoporous dodecahedron structure, N and S codoped carbon overlayer and deep‐rooted CNTs network, the product exhibits a larger‐than‐theoretical reversible Li‐storage capacity of 941 mAh g^?1 after 250 cycles at 100 mA g^?1 and excellent high‐rate capability (734, 591, 505 mAh g^?1 after 500 cycles at large current densities of 1, 2, and 5 A g^?1 , respectively).     

Unusually High Optical Transmission in Ca:Ag Blend Films: High‐Performance Top Electrodes for Efficient Organic Solar Cells

Highly transparent electrodes are demonstrated based on thermally evaporated calcium:silver blend thin–films, which show unusually high transmission well above the expectations from bulk material properties and thin film optics. These electrodes exhibit a low sheet resistance of 27.3 Ω/, combined with an extraordinarily high mean transmittance of 93.0% in the visible spectral range (σ_dc/σ_opt = 186.7), superior to the commonly used inorganic electrodes made from indium tin oxide (ITO). Additionally, the metal blend electrode is flexible, showing a constant sheet resistance down to a bending radius of 10 mm and can be employed on top of organic devices without causing damage to the organic material. The spontaneously formed unique microstructure of a polycrystalline Ag network with randomly distributed nanoapertures, surrounded by a calcium shell, enables broadband transmittance enhancement due to amplified plasmonic coupling. Consequently, top‐illuminated organic solar cells using such metal blend electrodes achieve a power conversion efficiency of 7.2% (which defines a new record for top illuminated organic solar cells) and even exceed the efficiency of similar bottom‐illuminated reference solar cells (6.9%) employing common ITO electrodes.     

Bimetal–Organic Framework: One‐Step Homogenous Formation and its Derived Mesoporous Ternary Metal Oxide Nanorod for High‐Capacity,High‐Rate,and Long‐Cycle‐Life Lithium Storage

Metal–organic frameworks (MOFs) and relative structures with uniform micro/mesoporous structures have shown important applications in various fields. This paper reports the synthesis of unprecedented mesoporous Ni_xCo_3?xO₄ nanorods with tuned composition from the Co/Ni bimetallic MOF precursor. The Co/Ni‐MOFs are prepared by a one‐step facile microwave‐assisted solvothermal method rather than surface metallic cation exchange on the preformed one‐metal MOF template, therefore displaying very uniform distribution of two species and high structural integrity. The obtained mesoporous Ni_0.3Co_2.7O₄ nanorod delivers a larger‐than‐theoretical reversible capacity of 1410 mAh g^?1 after 200 repetitive cycles at a small current of 100 mA g^?1 with an excellent high‐rate capability for lithium‐ion batteries. Large reversible capacities of 812 and 656 mAh g^?1 can also be retained after 500 cycles at large currents of 2 and 5 A g^?1, respectively. These outstanding electrochemical performances of the ternary metal oxide have been mainly attributed to its interconnected nanoparticle‐integrated mesoporous nanorod structure and the synergistic effect of two active metal oxide components.     

HPbI3: A New Precursor Compound for Highly Efficient Solution‐Processed Perovskite Solar Cells

Recently, there have been extensive research efforts on developing high performance organolead halide based perovskite solar cells. While most studies focused on optimizing the deposition processes of the perovskite films, the selection of the precursors has been rather limited to the lead halide/methylammonium (or formamidium) halide combination. In this work, we developed a new precursor, HPbI₃, to replace lead halide. The new precursor enables formation of highly uniform formamidium lead iodide (FAPbI₃) films through a one‐step spin‐coating process. Furthermore, the FAPbI₃ perovskite films exhibit a highly crystalline phase with strong (110) preferred orientation and excellent thermal stability. The planar heterojunction solar cells based on these perovskite films exhibit an average efficiency of 15.4% and champion efficiency of 17.5% under AM 1.5 G illumination. By comparing the morphology and formation process of the perovskite films fabricated from the formamidium iodide (FAI)/HPbI₃, FAI/PbI₂, and FAI/PbI₂ with HI additive precursor combinations, it is shown that the superior property of the HPbI₃ based perovskite films may originate from 1) a slow crystallization process involving exchange of H⁺ and FA⁺ ions in the PbI₆ octahedral framework and 2) elimination of water in the precursor solution state.     

Cooperative Effect of GO and Glucose on PEDOT:PSS for High VOC and Hysteresis‐Free Solution‐Processed Perovskite Solar Cells

Hybrid organic–inorganic halide perovskites have emerged at the forefront of solution‐processable photovoltaic devices. Being the perovskite precursor mixture a complex equilibrium of species, it is very difficult to predict/control their interactions with different substrates, thus the final film properties and device performances. Here the wettability of CH₃NH₃PbI₃ (MAPbI₃) onto poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) hole transporting layer is improved by exploiting the cooperative effect of graphene oxide (GO) and glucose inclusion. The glucose, in addition, triggers the reduction of GO, enhancing the conductivity of the PEDOT:PSS+GO+glucose based nanocomposite. The relevance of this approach toward photovoltaic applications is demonstrated by fabricating a hysteresis‐free MAPbI₃ solar cells displaying a ≈37% improvement in power conversion efficiency if compared to a device grown onto pristine PEDOT:PSS. Most importantly, V_OC reaches values over 1.05 V that are among the highest ever reported for PEDOT:PSS p‐i‐n device architecture, suggesting minimal recombination losses, high hole‐selectivity, and reduced trap density at the PEDOT:PSS along with optimized MAPbI₃ coverage.     

Wide Bandgap Molecular Acceptors with a Truxene Core for Efficient Nonfullerene Polymer Solar Cells: Linkage Position on Molecular Configuration and Photovoltaic Properties

Two wide bandgap star‐shaped small molecular acceptors, para‐TrBRCN and meta‐TrBRCN , are synthesized for efficient nonfullerene polymer solar cells (PSCs). The tiny structural variation by just changing the linkage positions affects largely the inherent properties of the resulting molecules. Both molecules have a nonplanar 3D structure, which can prevent the excessively aggregation to realize the optimized morphology and ideal domain size in their active blends. Compared to para‐TrBRCN , meta‐TrBRCN exhibits the smaller distortions between the truxene skeleton and the benzothiadiazole units, which would also lead to the enhanced π–π stacking and charge transfer. When blending with PTB7‐Th, high power conversion efficiencies (PCEs) of 10.15% and 8.28% are obtained for meta‐TrBRCN and para‐TrBRCN devices, respectively. To make up the weak absorption of above binary active blend in the longer wavelength region and increase the whole device performance further, low bandgap 3,9‐bis(2‐methylene‐(3‐(1,1‐dicyanomethylene)‐indanone)‐5,5,11,11‐tetrakis(4‐hexylthienyl)‐dithieno[2,3‐d:2′,3′‐d′]‐s‐indaceno[1,2‐b:5,6‐b′]‐dithiophene (ITIC‐Th) is added as the second acceptor material to fabricate ternary blend PSCs. After adding 20 wt% of ITIC‐Th, the resulting devices exhibit the well‐balanced optical absorption and fine‐tuned morphology, giving rise to the significantly improved PCE of 11.40% with much higher J _sc of 18.25 mA cm^?2 and fill factor of 70.2%.     

Metal Ion/Dendrimer Complexes with Tunable Work Functions in a Wide Range and Their Application as Electron‐ and Hole‐Transport Materials of Non‐Fullerene Organic Solar Cells

The work functions of electrodes can be modified by adding charge transport layers to have good energy level matching with the active materials for organic solar cells (OSCs). Usually, a certain material gives rise to one definite work function of an electrode. In this work it is demonstrated that complexes of poly(amido amine) (generation 3) (PAMAM) with Cu²⁺ can continuously tune the work function of indium tin oxide (ITO) in a range of 4–5 eV by controlling the ratio of Cu²⁺ to PAMAM. PAMAM can lower the work function of ITO from 4.60 to 4.07 eV, while Cu²⁺‐PAMAM can increase the work function. The work function increase depends on the Cu²⁺‐to‐PAMAM molar ratio, and the work function can be up to 4.96 eV. The Cu²⁺ effect is ascribed the Cu²⁺‐caused change in the dipole moment of PAMAM. Moreover, this method can be used to continuously modify the work function of other materials, including Ag, Au, poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate, and reduced graphene oxide. In addition, PAMAM and Cu²⁺‐PAMAM are investigated as the charge collection buffer materials of non‐fullerene OSCs of poly[(2,6‐(4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)‐benzo[1,2‐b:4,5‐b′]dithiophene))‐alt‐(5,5‐(1′,3′‐di‐2‐thienyl‐5′,7′‐bis(2‐ethylhexyl)benzo[1′,2′‐c:4′,5′‐c′]dithiophene‐4,8‐dione))]: 3,9‐bis(2‐methylene‐(3‐(1,1‐dicyanomethylene)‐indanone))‐5,5,11,11‐tetrakis(4‐hexylphenyl)‐dithieno[2,3‐d:2′,3′‐d′]‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene). The power conversion efficiency can reach 9.2%, which is comparable to that using conventional charge transport materials.     

Nanoporous Nitrogen‐Doped Graphene Oxide/Nickel Sulfide Composite Sheets Derived from a Metal‐Organic Framework as an Efficient Electrocatalyst for Hydrogen and Oxygen Evolution

Engineering of controlled hybrid nanocomposites creates one of the most exciting applications in the fields of energy materials and environmental science. The rational design and in situ synthesis of hierarchical porous nanocomposite sheets of nitrogen‐doped graphene oxide (NGO) and nickel sulfide (Ni₇S₆) derived from a hybrid of a well‐known nickel‐based metal‐organic framework (NiMOF‐74) using thiourea as a sulfur source are reported here. The nanoporous NGO/MOF composite is prepared through a solvothermal process in which Ni(II) metal centers of the MOF structure are chelated with nitrogen and oxygen functional groups of NGO. NGO/Ni₇S₆ exhibits bifunctional activity, capable of catalyzing both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) with excellent stability in alkaline electrolytes, due to its high surface area, high pore volume, and tailored reaction interface enabling the availability of active nickel sites, mass transport, and gas release. Depending on the nitrogen doping level, the properties of graphene oxide can be tuned toward, e.g., enhanced stability of the composite compared to commonly used RuO₂ under OER conditions. Hence, this work opens the door for the development of effective OER/HER electrocatalysts based on hierarchical porous graphene oxide composites with metal chalcogenides, which may replace expensive commercial catalysts such as RuO₂ and IrO₂.