Perovskite Photovoltaic Integrated CdS/TiO2 Photoanode for Unbiased Photoelectrochemical Hydrogen Generation

Perovskite-Solar-Cell-Powered Integrated Fuel Conversion and Energy-Storage Devices

Metal halide hybrid perovskite solar cells (PSCs) have received considerable attention over the past decade owing to their potential for low-cost, solution-processable, earth-abundant, and high-performance superiority, increasing power conversion efficiencies of up to 25.7%. Solar energy conversion into electricity is highly efficient and sustainable, but direct utilization, storage, and poor energy diversity are difficult to achieve, resulting in a potential waste of resources. Considering its convenience and feasibility, converting solar energy into chemical fuels is regarded as a promising pathway for boosting energy diversity and expanding its utilization. In addition, the energy conversion-storage integrated system can efficiently sequentially capture, convert, and store energy in electrochemical energy storage devices. However, a comprehensive overview focusing on PSC-self-driven integrated devices with a discussion of their development and limitations remains lacking. Here, focus is on the development of representative configurations of emerging PSC-based photo-electrochemical devices including self-charging power packs, unassisted solar water splitting/CO2 reduction. The advanced progresses in this field, including configuration design, key parameters, working principles, integration strategies, electrode materials, and their performance evaluations are also summarized. Finally, scientific challenges and future perspectives for ongoing research in this field are presented.

Research progresses on the application of perovskite in adsorption and photocatalytic removal of water pollutants

The problem of global water pollution and scarcity of water resources is becoming increasingly serious. Multifunctional perovskites can well drive adsorption and photocatalytic reactions to remove water pollutants. There are many advantages of perovskites, such as abundant oxygen vacancies, easily tunable structural morphology, stable crystal state, highly active metal sites, and a wide photo response range. However, there are few reviews on the simultaneous application of perovskite to adsorption and photocatalytic removal of water pollutants. Thus, this paper discusses the preparation methods of perovskite, the factors affecting the adsorption of water environmental pollutants by perovskite, and the factors affecting perovskite photocatalytic water pollutants. The particle size, specific surface area, oxygen vacancies, electron-hole trapping agents, potentials of the valence band, and conduction band in perovskites are significant influencing factors for adsorption and photocatalysis. Strategies for improving the performance of perovskites in the fields of adsorption and photocatalysis are discussed. The adsorption behaviors and catalytic mechanisms are also investigated, including adsorption kinetics and thermodynamics, electrostatic interaction, ion exchange, chemical bonding, and photocatalytic mechanism. It summarizes the removal of water pollutants by using perovskites. It provides the design of perovskites as high-efficiency adsorbents and catalysts for developing new technologies.

Solar-to-Chemical Fuel Conversion via Metal Halide Perovskite Solar-Driven Electrocatalysis

Sunlight is an abundant and clean energy source, the harvesting of which could make a significant contribution to society's increasing energy demands. Metal halide perovskites (MHP) have recently received attention for solar fuel generation through photocatalysis and solar-driven electrocatalysis. However, MHP photocatalysis is limited by low solar energy conversion efficiency, poor stability, and impractical reaction conditions. Compared to photocatalysis, MHP solar-driven electrocatalysis not only exhibits higher solar conversion efficiency but also is more stable when operating under practical reaction conditions. In this Perspective, we outline three leading types of MHP solar-driven electrocatalysis device technologies now in the research spotlight, namely, (1) photovoltaic-electrochemical (PV-EC), (2) photovoltaic-photoelectrochemical (PV-PEC), and (3) photoelectrochemical (PEC) approaches for solar-to-fuel reactions, including water-splitting and the CO₂ reduction reaction. In addition, we compare each technology to show their relative technical advantages and limitations and highlight promising research directions for the rapidly emerging scientific field of MHP-based solar-driven electrocatalysis.

Noble-Metal-Free Multicomponent Nanointegration for Sustainable Energy Conversion

Global energy and environmental crises are among the most pressing challenges facing humankind. To overcome these challenges, recent years have seen an upsurge of interest in the development and production of renewable chemical fuels as alternatives to the nonrenewable and high-polluting fossil fuels. Photocatalysis, photoelectrocatalysis, and electrocatalysis provide promising avenues for sustainable energy conversion. Single- and dual-component catalytic systems based on nanomaterials have been intensively studied for decades, but their intrinsic weaknesses hamper their practical applications. Multicomponent nanomaterial-based systems, consisting of three or more components with at least one component in the nanoscale, have recently emerged. The multiple components are integrated together to create synergistic effects and hence overcome the limitation for outperformance. Such higher-efficiency systems based on nanomaterials will potentially bring an additional benefit in balance-of-system costs if they exclude the use of noble metals, considering the expense and sustainability. It is therefore timely to review the research in this field, providing guidance in the development of noble-metal-free multicomponent nanointegration for sustainable energy conversion. In this work, we first recall the fundamentals of catalysis by nanomaterials, multicomponent nanointegration, and reactor configuration for water splitting, CO₂ reduction, and N₂ reduction. We then systematically review and discuss recent advances in multicomponent-based photocatalytic, photoelectrochemical, and electrochemical systems based on nanomaterials. On the basis of these systems, we further laterally evaluate different multicomponent integration strategies and highlight their impacts on catalytic activity, performance stability, and product selectivity. Finally, we provide conclusions and future prospects for multicomponent nanointegration. This work offers comprehensive insights into the development of cost-competitive multicomponent nanomaterial-based systems for sustainable energy-conversion technologies and assists researchers working toward addressing the global challenges in energy and the environment.

Enhanced Photoelectrochemical Water Oxidation Performance in Bilayer TiO2 /α-Fe2 O3 Nanorod Arrays Photoanode with Cu : NiOx as Hole Transport Layer and Co-Pi as Cocatalyst

Efficient charge transfer and excellent surface water oxidation kinetics are key factors in determining the photoelectrochemical (PEC) water splitting performance in photoelectrodes. Herein, a bilayer TiO₂ /α-Fe₂ O₃ nanorod (NR) arrays photoanode was prepared with deposited Cu-doped NiO_x (Cu : NiO_x ) hole transport layer (HTL) and Co-Pi oxygen evolution reaction (OER) cocatalyst for PEC water oxidation. The hierarchical TiO₂ /α-Fe₂ O₃ composite obtained by a secondary hydrothermal process exhibited an inapparent bilayer structure by embedding the underlayer TiO₂ NR arrays at the bottom part of the post-grown α-Fe₂ O₃ NR arrays. The underlayer TiO₂ NRs acted as an effective shuttling pathway for transferring photoelectrons generated in the upper hematite light absorber layer. A p-type inter-Cu : NiO_x HTL was introduced to form a build-in p-n electric field between Cu : NiO_x and α-Fe₂ O₃ NRs, which improved the hole extraction from α-Fe₂ O₃ to Co-Pi OER catalyst. As expected, the as-engineered TiO₂ /α-Fe₂ O₃ /Cu : NiO_x /Co-Pi photoanode displayed an excellent photocurrent density of 2.43 mA cm^-2 at 1.23 V versus the reversible hydrogen electrode (V_RHE ), up to 4.05 and 2.23 times greater than those of the bare α-Fe₂ O₃ (0.60 mA cm^-2 ) and TiO₂ /α-Fe₂ O₃ , respectively. The results demonstrate that the bottom-up engineering of electron-hole transport channels and cocatalyst modification is an attractive maneuver to enhance the PEC water oxidation activity in hematite and other photoanodes.

Photoelectrochemical water splitting by hybrid organic-inorganic systems: setting the path from 2% to 20% solar-to-hydrogen conversion efficiency

Promoting solar fuels as a viable alternative to hydrocarbons calls for technologies that couple efficiency, durability, and low cost. In this work we elucidate how hybrid organic-inorganic systems employing hybrid photocathodes (HPC) and perovskite solar cells (PSC) could eventually match these needs, enabling sustainable and clean hydrogen production. First, we demonstrate a system comprising an HPC, a PSC, and a Ru-based oxygen evolution catalyst reaching a solar-to-hydrogen (STH) efficiency above 2%. Moving from this experimental result, we elaborate a perspective for this technology by adapting the existing models to the specific case of an HPC-PSC tandem. We found two very promising scenarios: one with a 10% STH efficiency, achievable using the currently available semiconducting polymers and the widely used methylammonium lead iodide (MAPI) PSC, and the other one with a 20% STH efficiency, requiring dedicated development for water-splitting applications of recently reported high-performing organic semiconductors and narrow band-gap perovskites.

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2% STH efficiency with a hybrid photocathode/perovskite solar cell tandem system

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Multi-variable optimization tool used to find the optimal parameters to maximize STH

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Optimized photocathode parameters are found in order to reach the 10% STH goal

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Long-term scenario with 20% STH is predicted for hybrid organic tandem systems

Recent Progress in Designing Halide-Perovskite-Based System for the Photocatalytic Applications

The halide perovskite material has attracted vast attention as a versatile semiconductor in the past decade. With the unique advantages in physical and chemical properties, they have also shown great potential in photocatalytic applications. This review aims at the specific design principles triggered by the unique properties when employing halide-perovskite-based photocatalytic systems from the following perspectives: (I) Design of photoelectrocatalytic device structures including the n-i-p/p-i-n structure, photoelectrode device encapsulation, and electrolyte engineering. (II) The design of heterogeneous photocatalytic systems toward the hydrogen evolution reaction (HER) and CO2 reduction reaction, including the light management, surface/interface engineering, stability improvement, product selectivity engineering, and reaction system engineering. (III) The photocatalysts for the environmental application and organic synthesis. Based on the analyses, the review also suggests the prospective research for the future development of halide-perovskite-based photocatalytic systems.

Self-Powered Perovskite/CdS Heterostructure Photodetectors

Methylammonium lead halide perovskites have gained a lot of attention because of their remarkable physical properties and potential for numerous (opto)electronic applications. Here, high-performance photodetectors based on CH₃NH₃PbI₃ (MAPbI₃)/CdS heterostructures are demonstrated. The resulting self-powered MAPbI₃/CdS photodetectors show excellent operating characteristics including a maximum detectivity of 2.3 × 10¹¹ Jones with a responsivity of 0.43 A/W measured at 730 nm. A temporal response time of less than 14 ms was achieved. The mechanisms of charge separation and transport at the interface of the MAPbI₃/CdS junction were investigated via conductive atomic force microscopy (AFM) and photoconductive AFM. Obtained results show that grain boundaries exhibit higher photocurrent than flat regions of the top perovskite layer, which indicates that excitons preferentially separate at the grain boundaries of the perovskite thin film, that is, at the edges of the MAPbI₃ crystals. The study of the photoelectric mechanism at the nanoscale suggests the device performance could potentially be fine-tuned through grain boundary engineering, which provides essential insights for the fabrication of the high-performance photodetector. The demonstrated self-powered photodetector is promising for numerous applications in low-energy consumption optoelectronic devices.

Hierarchical SnS2/CuInS2 Nanosheet Heterostructure Films Decorated with C60 for Remarkable Photoelectrochemical Water Splitting

Rational architectural design and catalyst components are beneficial to improve the photoelectrochemical (PEC) performance. Herein, hierarchical SnS₂/CuInS₂ nanosheet heterostructure porous films were fabricated and decorated with C₆₀ to form photocathodes for PEC water reduction. Large-size CuInS₂ nanosheet films were first grown on transparent conducting glass to form substrate films. Then, small-size SnS₂ nanosheets were epitaxially grown on both sides of the CuInS₂ nanosheets to form uniform hierarchical porous laminar films. The addition of C₆₀ on the surface of the SnS₂/CuInS₂ porous nanosheets effectively increased visible light absorption of the composite photocathode. Photoluminescence spectroscopy and impedance spectroscopy analyses indicated that the formation of a SnS₂/CuInS₂ heterojunction and decoration of C₆₀ significantly increased the photocurrent density by promoting the electron-hole separation and decreasing the resistance to the transport of charge carriers. The hierarchical SnS₂/CuInS₂ nanosheet heterostructure porous films containing multiscale nanosheets and pore configurations can enlarge the surface area and enhance visible light utilization. These beneficial factors make the optimized C₆₀-decorated SnS₂/CuInS₂ photocathode exhibit much higher photocathodic current (4.51 mA cm^-2 at applied potential -0.45 V vs reversible hydrogen electrode ) and stability than the individual CuInS₂ (2.58 mA cm^-2) and SnS₂ (1.92 mA cm^-2) nanosheet film photocathodes. This study not only reveals the promise of C₆₀-decorated hierarchical SnS₂/CuInS₂ nanosheet heterostructure porous film photocathodes for efficient solar energy harvesting and conversion but also provides rational guidelines in designing high-efficiency photoelectrodes from earth-abundant and low-cost materials allowing widely practical applications.