Suppressed Charge Recombination Research Articles

High‐Performing Quasi‐2D Perovskite Photodetectors with Efficient Charge Transport Network Built from Vertically Orientated and Evenly Distributed 3D‐Like Phases

AbstractQuasi‐two‐dimensional (Q‐2D) perovskites are emerging as one of the most promising materials for photodetectors. However, a significant challenge to Q‐2D perovskites for photodetection is their insufficient charge transport ability, which is mainly attributed to their hybrid low‐dimensional n‐phase structure. This study demonstrates that evenly‐distributed 3D‐like phases with vertical orientation throughout the film can greatly facilitate charge transport and suppress charge recombination, outperforming the prevalent phase structure with a vertical dimension gradient. Based on such a phase structure, a Q‐2D Ruddlesden−Popper perovskite self‐powered photodetector achieving a combination of exceptional figures‐of‐merit is realized, including a responsivity of 0.45 AW−1, a peak specific detectivity of 2.3 × 1013 Jones, a 156 dB linear dynamic range, and a rise/fall time of 2.89 µs/1.93 µs. The desired phase structure is obtained by utilizing a double‐hole transport layer (HTL), combining hydrophobic PTAA and hydrophilic PEDOT: PSS. Besides, the dependence of the hybrid low‐dimensional phase structure is also identified on the surface energy of the buried HTL substrate. This study gives insight into the correlation between Q‐2D perovskites’ phase structure and performance, providing a valuable design guide for Q‐2D perovskite‐based photodetectors.

Highly efficient binuclear cobalt-bis(4-methylthiosemicarbazone) complex co-catalyst to support Cd0.5Zn0.5S NPs for enhanced photocatalytic hydrogen evolution

Photocatalytic water splitting to produce H2 is a promising method to directly convert solar energy into chemical energy, which is a superb solution to the human energy shortage. This work constructed an efficient photocatalyst using Cd0.5Zn0.5S NPs (CZS) as the photosensitizer, water-soluble binuclear cobalt bis(4-methothiocarbazide) complex as the molecular co-catalyst. The complex could effectively transport photogenerated electrons on CZS, thus inhibiting charge recombination and significantly improving the activity and stability of the present photocatalytic system. Under optimal conditions, the experimental results showed that the highest turnover number (TON) of H2 production was 5699 after the reaction of the photocatalytic system with visible light (λ > 420 nm) for 24 h. The average H2 evolution rate of 1221 μmol∙h−1 was 6.4 times higher than that of pure CZS. The highest apparent quantum yield (AQY) at 420 nm was ∼26%.

Titania nanorods array homojunction with sub-stoichiometric TiO2 for enhanced methylene blue photodegradation

TiO2 thin films are known to promote photodegradation of dyes and pollutants in water solution via heterogeneous photocatalysis. This ability is guided by the photoexcitation through photons having energies above the band gap. To improve photocatalytic activity, nanostructures with high surface area can be applied, which can ease molecular adsorption/desorption mechanisms, enhance electronic transfer properties and lower excitation energy. For this purpose, square cross-section TiO2 vertically aligned nanorod (TNR) array configuration has been chosen as a semiconductor substrate. On top of it, a thin layer of sub-stoichiometric TiO2−x has been deposited, aiming at inducing a vacancy doped homojunction between two different oxygen rich/deficient TiO2 layers, possibly leading to lower band gap and enhanced photochemical activity. In principle, promotion of electron and holes separation and suppression of charge recombination could occur. Vertically aligned TNRs have been deposited through a hydrothermal growth in acidic conditions on a pre-seeded glass conducting substrate, optimizing the seeding process through spin coating. Sub-stoichiometric TiO2−x layer (50 nm nominal thickness) has been deposited on top of TNRs via radiofrequency magnetron sputtering at three different stoichiometries, tuning the oxygen partial pressure in sputtering argon atmosphere at 10 %, 15 % and 20 %, respectively. Photocatalytic activity has been investigated in the photodegradation of an aqueous solution of methylene blue, both under UV and simulated solar light irradiation at room temperature and atmospheric pressure, resulting in the degradation of methylene blue target molecule up to 99 % under UV and 85 % under simulated solar irradiation after 6 h. These promising achievements unlock new environmental applications for enhanced dye degradation industrial processes.

Cd/Pt Precursor Solution for Solar H2 Production and in situ Photochemical Synthesis of Pt Single-atom Decorated CdS Nanoparticles.

Despite extensive efforts to develop high-performance H2 evolution catalysts, this remains a major challenge. Here, we demonstrate the use of Cd/Pt precursor solutions for significant photocatalytic H2 production (154.7 mmol g-1 h-1 ), removing the need for a pre-synthesized photocatalyst. In addition, we also report simultaneous in situ synthesis of Pt single-atoms anchored CdS nanoparticles (PtSA -CdSIS ) during photoirradiation. The highly dispersed in situ incorporation of extensive Pt single atoms on CdSIS enables the enhancement of active sites and suppresses charge recombination, which results in exceptionally high solar-to-hydrogen conversion efficiency of ≈1 % and an apparent quantum yield of over 91 % (365 nm) for H2 production. Our work not only provides a promising strategy for maximising H2 production efficiency but also provides a green process for H2 production and the synthesis of highly photoactive PtSA -CdSIS nanoparticles.

Cd/Pt Precursor Solution for Solar H2 Production and in situ Photochemical Synthesis of Pt Single‐atom Decorated CdS Nanoparticles

AbstractDespite extensive efforts to develop high‐performance H2 evolution catalysts, this remains a major challenge. Here, we demonstrate the use of Cd/Pt precursor solutions for significant photocatalytic H2 production (154.7 mmol g−1 h−1), removing the need for a pre‐synthesized photocatalyst. In addition, we also report simultaneous in situ synthesis of Pt single‐atoms anchored CdS nanoparticles (PtSA‐CdSIS) during photoirradiation. The highly dispersed in situ incorporation of extensive Pt single atoms on CdSIS enables the enhancement of active sites and suppresses charge recombination, which results in exceptionally high solar‐to‐hydrogen conversion efficiency of ≈1 % and an apparent quantum yield of over 91 % (365 nm) for H2 production. Our work not only provides a promising strategy for maximising H2 production efficiency but also provides a green process for H2 production and the synthesis of highly photoactive PtSA‐CdSIS nanoparticles.

Manipulating Polymer Backbone Configuration via Halogenated Asymmetric End-Groups Enables Over 18% Efficiency All-Polymer Solar Cells.

High-performance all-polymer solar cells (all-PSCs) deeply rely on the joint contributions of desirable optical absorption, adaptive energy levels, and appropriate morphology. Herein, two structural analogous polymerized small-molecule acceptors (PSMAs), PYFCl-T and PYF&PYCl-T, are synthesized, and then incorporated into the PM6:PY-IT binary blends to construct ternary all-PSCs. Due to the superior compatibility of PY-IT and PYFCl-T, theternary all-PSC based on PM6:PY-IT:PYFCl-T with 10 wt% PYFCl-T, presents higher and more balanced charge mobility, suppressed charge recombination, and faster charge-transfer kinetics, resulting in an outstanding power conversion efficiency (PCE) of 18.12% with enhanced Jsc and FF, which is much higher than that (PCE of 16.09%) of the binary all-PSCs based on PM6:PY-IT. Besides, the ternary all-PSCs also exhibit improved photostability. The conspicuous performance enhancement principally should give the credit to the miscibility-driven phase optimization of the donor and acceptor. These findings highlight the significance of polymer-backbone configuration modulation of PSMAs in morphology optimization toward boosting the device properties of all-PSCs.

Lifetime over 10000 hours for organic solar cells with Ir/IrOx electron-transporting layer

The stability of organic solar cells is a key issue to promote practical applications. Herein, we demonstrate that the device performance of organic solar cells is enhanced by an Ir/IrOx electron-transporting layer, benefiting from its suitable work function and heterogeneous distribution of surface energy in nanoscale. Notably, the champion Ir/IrOx-based devices exhibit superior stabilities under shelf storing (T80 = 56696 h), thermal aging (T70 = 13920 h), and maximum power point tracking (T80 = 1058 h), compared to the ZnO-based devices. It can be attributed to the stable morphology of photoactive layer resulting from the optimized molecular distribution of the donor and acceptor and the absence of photocatalysis in the Ir/IrOx-based devices, which helps to maintain the improved charge extraction and inhibited charge recombination in the aged devices. This work provides a reliable and efficient electron-transporting material toward stable organic solar cells.

Aggregation Triggers Red/Near-Infrared Light Hydrogen Production of Organic Dyes with High Efficiency

Integrating broad-band red/near-infrared (NIR) light harvesting and efficient charge separation in a semiconductor is a crucial prerequisite for the realization of high photocatalytic efficiency but remains a challenge. Here, we discover that eosin Y (EY) aggregates exhibit strong red/NIR-light harvesting induced by electronic couplings between adjacent EY molecules. Simultaneously, the aggregates are favorable for exciton dissociation and formation of charge-separation states, greatly inhibiting charge recombination. The quantum yield (QY) of EY aggregates for hydrogen production highly reaches 23.6% at 610 nm. More importantly, this general concept of aggregation-induced red/NIR-light photocatalysis was observed in a series of typical organic dyes (11 examples). Impressively, the QY of cobalt phthalocyanin aggregates for hydrogen production is calculated to be 17.2% at 800 nm, which is the highest value among NIR-light-driven H2-evolution systems (≥800 nm) ever reported. This study unlocks a fresh realm of artificial photosynthesis, which uses dye aggregates for red/NIR-light solar conversion.

Selective Valorization of Glycerol to Formic Acid on a BiVO4 Photoanode through NiFe Phenolic Networks.

The integration of the glycerol oxidation reaction (GOR) with the hydrogen evolution reaction in photoelectrochemical (PEC) cells is a desirable alternative to PEC water splitting since a large quantity of glycerol is easily accessible as the byproduct from the biodiesel industry. However, the PEC valorization of glycerol to the value-added products suffers from low Faradaic efficiency and selectivity, especially in acidic conditions, which is beneficial for hydrogen production. Herein, by loading bismuth vanadate (BVO) with a robust catalyst composed of phenolic ligands (tannic acid) coordinated with Ni and Fe ions (TANF), we demonstrate a modified BVO/TANF photoanode for the GOR with a remarkable Faradaic efficiency of over 94% to value-added molecules in a 0.1 M Na2SO4/H2SO4 (pH = 2) electrolyte. The BVO/TANF photoanode achieved a high photocurrent of 5.26 mA·cm-2 at 1.23 V versus reversible hydrogen electrode under 100 mW/cm2 white light irradiation for formic acid production with 85% selectivity, equivalent to 573 mmol/(m2·h). Transient photocurrent and transient photovoltage techniques and electrochemical impedance spectroscopy along with intensity-modulated photocurrent spectroscopy indicated that the TANF catalyst could accelerate hole transfer kinetics and suppress charge recombination. Comprehensive mechanistic investigations reveal that the GOR is initiated by the photogenerated holes of BVO, while the high selectivity to formic acid is attributed to the selective adsorption of primary hydroxyl groups in glycerol on TANF. This study provides a promising avenue for highly efficient and selective formic acid generation from biomass in acid media via PEC cells.

Multifunctional Molecule Assists Passivate Method to Simultaneously Improve the Efficiency and Stability of Perovskite Solar Cells.

The power conversion efficiency (PCE) of perovskite solar cells (PSCs) has been greatly improved recently. However, in organic-inorganic polycrystalline perovskite films many defects inevitably exist, which limits the PCE and stability of PSCs. Herein, a small organic molecule 2-chlorothiazole-4-carboxylic acid (SN) is spin coated on a perovskite film to enhance the performance of PSCs. We find that the multifunctional molecule SN reacts with under-coordinated Pb2+ ions and I- vacancies because of the presence of the sulfur and nitrogen donor atoms, and the -COOH groups, which are conducive to suppressing charge recombination and passivating defects. Even more, the introduction of the SN layer can effectively adjust the energy level alignment, which is conducive to the separation and extraction of charge carriers in PSCs. Therefore, devices with SN modification show a champion PCE of 22.55 %. Besides, PSCs with SN show impressive stability, retaining 96 % of its initial PCE after storage in ambient air for 500 h.

Simultaneous bottom-up double-layer synergistic engineering by multifunctional natural molecules for efficient and stable SnO2-based planar perovskite solar cells

The performance and stability of perovskite solar cells (PSCs) is limited by detrimental defects, mostly distributed at the grain boundary (GB) of bulk perovskite film and interface, which induce serious carrier non-radiative recombination. Therefore, there is particularly urgent to realize simultaneous passivation of bulk defects and interfacial defects. In this work, a simple, low-cost and effective multifunctional modification strategy is developed by introducing the λ-Carrageenan (λ-C) as the interfacial layer of SnO2/perovskite. The sulfate groups of λ-C not only play a positive role in passivating the Sn4+ from SnO2 film, resulting in high conductivity, but also effectively passivate the defects at the SnO2/perovskite interface. Meanwhile, λ-C can effectively passivate the defects in the perovskite film due to the strong binding force between the high content of sulfate groups and PbI2. The synergistic effect of λ-C simultaneously achieves interfacial defects and bulk defects passivation, better crystalline quality, suppressed charge recombination, released interfacial stress and more favorable interfacial energy level alignment. Based on the above efficient synergy, the λ-C-modified device achieves a high efficiency of 23.81%, which is ∼24.53% higher than the control device (19.12%). To our best knowledge, 23.81% of power conversion efficiency (PCE) is the highest reported PCE value of PSCs employing green natural additives. Moreover, long-term and thermal stabilities are significantly improved after interface modification. Thus, this work provides an idea for developing multifunctional natural materials towards the attainment of the efficient and stable PSCs.

Weakly Hydrophilic Imine-Linked Covalent Benzene-Acetylene Frameworks for Photocatalytic H2O2 Production in the Two-Phase System.

Conversing oxygen (O2) to hydrogen peroxide (H2O2) driven by solar energy is a promising H2O2 onsite production route but often short of efficient and durable photocatalysts. Herein, strong π-π conjugate polycyclic aromatic benzene and acetylene units have been constructed into new covalent organic frameworks (COFs) linked by imine C═N bonding. These COFs demonstrated two-dimensional hexagonal crystalline frameworks with higher crystallinity and larger surface area (>600 m2 g-1). Covalent benzene-acetylene frameworks possessed appropriate visible light-responsive band structure and the suppressed charge recombination rate. The -OH groups on their frameworks enable them to be weakly hydrophilic. As a result, it served as high-performance but durable photocatalysts for H2O2 production in the water-benzyl alcohol (BA) two-phase system. It delivered a H2O2 production rate of 1240 μmol h-1 gcat-1 and durable catalytic efficiency within 60 h, comparable to the best COF-based catalysts. This study provides an efficient two-phase photocatalytic system for H2O2 production based on weakly hydrophilic imine-linked benzene-acetylene organic photocatalysts.

Efficient organic solar cells by modulating photoactive layer morphology with halogen-free additives

Optimizing the morphology of the photoactive layer by additives strategy is one of the successful methods for increasing efficiency in organic solar cells (OSCs). In this work, a halogen-free solvent additive, methoxy methyl phenyl sulfide (MMPS) added to the PTB7-Th:PC71BM-based system to improve the optoelectronic property for OSCs by modulating the phase separation and crystallinity in the photoactive layer. It is found that the addition of MMPS could well modulate the aggregation and diffusion of donor and acceptor to form an excellent bicontinuous interpenetrating network, which improved exciton dissociation enhanced charge transport and significantly inhibited charge recombination. Consequently, the PCE of device based on the PTB7-Th:PC71BM blend with 3% MMPS is 9.24%, which is a 92.5% efficiency improvement compared to the device without additives. These results indicate that our work effectively optimizes the performance parameters of devices, providing new ideas for the preparation of OSCs on a large scale and industrialization.

Enhanced carrier management via optimized SnO2 preparation and film coverage for improved device performance

Optimized electron transport layers (ETLs) can highly promote charge extraction and reduce carrier depopulation. Herein, tin oxide (SnO2) nanocrystals were prepared with the addition of citric acid to suppress SnO2 aggregation and achieve complete film coverage. The dense and uniform SnO2 films with smaller grain sizes will apparently enhance the external quantum efficiency and alleviate the J–V hysteresis behavior. The improved SnO2 film coverage can also passivate traps at ETL/perovskite interfaces and markedly suppress charge recombination to promote rapid carrier injection from perovskite to SnO2. Surely, the optimized SnO2 shows better electrical properties and device performance than Alfa-SnO2. In addition, the diblock-polymer of (PEO)120-(PPO)30 was incorporated into perovskite films to passivate defects and improve device stability. A power conversion efficiency of 23.12% [a VOC of 1.164 V, a JSC of 24.46 mA cm−2, and a fill factor (FF) of 0.812] for the best-performing device is achieved. The charge dynamics (separation, transport, and extraction) were also analyzed using characterization techniques. The optimized device will largely enhance carrier management and light-harvesting performance, and the controlled SnO2 can also open up an effective way to achieve scalable preparation and commercialization of perovskite solar cells.

P-N Heterojunction System Eu-Doped ZnO@GO for Photocatalytic Water Splitting.

Here, a feather-like Eu-doped ZnO (particle size ≈34.87µm and E g ≈3.13eV) nanoassembly is synthesized by using the capping agent cetyltrimethylammonium bromide-supported hydrothermal method. The Eu-doped ZnO is loaded onto the graphene oxide (GO) surface as Eu-doped ZnO@GO (particle size ≈23.07µm and E g≈0.79eV) and applied to measure the photocatalytic water splitting activity in 20% CH3OH under a 300W Xe light source. Eu-doped ZnO@GO exhibits the higher hydrogen generation activity of 255.8µmolh-1g-1 that is 159 and 1.5 times more than the pristine GO and Eu-doped ZnO systems, respectively. Eu-doped ZnO enhances the photocatalytic activity of GO because the p-n junction formed between GO and Eu-doped ZnO might support the charge-transfer and suppress charge recombination. The light harvesting power of Eu-doped ZnO@GO makes the charge transfer smooth through the GO network. Surface photovoltage and electrochemical impedance studies of the Eu-doped ZnO@GO composite, reveal that GO acts as the p-type semiconductor and Eu-doped ZnO works as an n-type semiconductor and their interface facilitates the p-n junction to ease charge separation and results in enhanced the water-splitting efficiency.

Recent Clay-Based Photocatalysts for Wastewater Treatment

Photocatalysis is a remarkable methodology that is popular and applied in different interdisciplinary research areas such as the degradation of hazardous organic contaminants in wastewater. In recent years, clay-based photocatalyst composites have attracted significant attention in the field of photocatalysis owing to their abundance, excellent light response ability, and stability. This review describes the combination of clay with focusing photocatalysts such as TiO2, g-C3N4, and Bi-based compounds for degrading organic pollutants in wastewater. Clay-based composites have more active surface sites, resulting in inhibited photocatalyst particle agglomeration. Moreover, clay enhances the creation of active radicals for organic pollutant degradation by separating photogenerated electrons and holes. Thus, the functions of clay in clay-based photocatalysts are not only to act as a template to inhibit the agglomeration of the main photocatalysts but also to suppress charge recombination, which may lengthen the electron–hole pair’s lifespan and boost degrading activity. Moreover, several types of clay-based photocatalysts, such as the clay type and main photocatalyst, were compared to understand the function of clay and the interaction of clay with the main photocatalyst. Thus, this study summarizes the recent clay-based photocatalysts for wastewater remediation and concludes that clay-based photocatalysts have considerable potential for low-cost, solar-powered environmental treatment.

Phosphotungstate-Based Anode Interfacial Material for Constructing High-Performance Polymer Solar Cells with a Fill Factor over 80.

In the field of organic solar cells (OSCs), the interfacial layer plays the role of enhancing carrier extraction/transportation, inhibiting their recombination, etc. In contrast to the wide variety of cathode interfacial materials with good modification ability, much less effort has been reported for anode interfacial materials. In this study, we report a polyoxometalate-based inorganic molecular cluster, zinc phosphotungstate (Zn3P2W24O80, denoted ZnPW), as an anode interfacial layer. Based on the PM6/EH-HD-4F/L8-BO-F ternary system, the device with ZnPW modification achieved a high power conversion efficiency (PCE) and a fill factor of up to 18.67 and 80.29%, respectively, which are higher than the counterpart device (PCE of 18.01%) with PEDOT/PSS as the anode interfacial layer. Detailed studies revealed that under the modification of ZnPW, the devices obtained promoted light absorption and suitable energy level matching between the active layer and the electrode, reduced contact resistance, and suppressed charge recombination. In addition, the ZnPW-modified devices had improved photostability and storage stability compared to PEDOT/PSS-modified devices. Our work shows that the polyoxometalate-based inorganic nanocluster ZnPW has great advantages in enhancing the device performance and stability of OSCs.

Passivation of Hematite by a Semiconducting Overlayer Reduces Charge Recombination: An Insight from Nonadiabatic Molecular Dynamics.

Hematite (α-Fe2O3) is a promising photoanode material for photoelectrochemical water splitting. Surface-passivating layers are effective in improving water oxidation kinetics; however, the passivation mechanism is not fully understood due to the complexity of interfacial reactions. Focusing on the Fe-terminated Fe2O3 (0001) surface that exhibits surface states in the band gap, we perform ab initio quantum dynamics simulations to study the effect of an α-Ga2O3 overlayer on charge recombination. The overlayer eliminates surface states and suppresses charge recombination 4-fold. This explains in part the observed cathodic shift in the onset potential for water oxidation. The increased charge carrier lifetime is an outcome of two factors, energy gap and electron-vibrational coupling, with a positive contribution from the former but a negative contribution from the latter. This work presents an advance in the atomistic time-domain understanding of the influence of surface passivation on charge recombination dynamics and provides guidance for designing novel α-Fe2O3 photoanodes.

Diethanolamine Modified Perovskite-Substrate Interface for Realizing Efficient ESL-Free PSCs.

Simplifying device layout, particularly avoiding the complex fabrication steps and multiple high-temperature treatment requirements for electron-selective layers (ESLs) have made ESL-free perovskite solar cells (PSCs) attractive. However, the poor perovskite/substrate interface and inadequate quality of solution-processed perovskite thin films induce inefficient interfacial-charge extraction, limiting the power conversion efficiency (PCEs) of ESL-free PSCs. A highly compact and homogenous perovskite thin film with large grains was formed here by inserting an interfacial monolayer of diethanolamine (DEA) molecules between the perovskite and ITO substrate. In addition, the DEA created a favorable dipole layer at the interface of perovskite and ITO substrate by molecular adsorption, which suppressed charge recombination. Comparatively, PSCs based on DEA-treated ITO substrates delivered PCEs of up to 20.77%, one of the highest among ESL-free PSCs. Additionally, this technique successfully elongates the lifespan of ESL-free PSCs as 80% of the initial PCE was maintained after 550 h under AM 1.5 G irradiation at ambient temperature.

Manipulating electronic structure and light absorption of carbon nitride via P-doping and local crystallization for efficient photocatalytic reduction of CO2

Graphitic carbon nitride (g-C3N4, CN) with high light harvesting and suppressed charge recombination is desired in photocatalytic reactions. Herein, locally crystalline CN (KP/CN) with photoresponse edge of 648 nm was synthesized by a two-step calcination method. First step was P-doping via calcining phytic acid and nitrogen-containing precursor. Another was local crystallinity tailoring via calcining with KSCN. The obtained KP/CN facilitated the n → π* electronic transition, exhibited improved light utilization and charge mobility. Theoretical calculations confirmed that CO2 adsorption and activation became easy on KP/CN-2. The yields of CO and CH4 under KP/CN catalysis were 58.7 and 29.0 μmol g−1, respectively, after 5 h in the presence of 0.5 mL water. This work demonstrated the synergistic enhancement of light absorption and charge carrier dissociation via doping and partial crystallization.