Suppressed Charge Recombination Research Articles

Enhancing the Stability and Efficiency of Inverted Perovskite Solar Cells with a Mixed Ammonium Ligands Passivation Strategy.

The perovskite solar cell (PSC), which has achieved efficiencies of more than 26%, is expected to be a promising technology that can alternate silicon-based solar cells. However, the performance of PSCs is still limited due to defects and ion migration that occur at the large number of grain boundaries present in perovskite thin films. In this study, the mixed ammonium ligands passivation strategy (MAPS) is demonstrated, which combines n-octylammonium iodide (OAI) and 1,3-diaminopropane (DAP) can effectively suppress the grain boundary defects and ion migration through grain boundaries by the synergistic effect of OAI and DAP, resulting in improved efficiency and stability of PSCs. It has also been revealed that MAPS not only enhances crystallinity and reduces grain boundaries but also improves charge transport while suppressing charge recombination. The MAPS-based opaque PSC shows the best power conversion efficiency (PCE) of 21.29% with improved open-circuit voltage (VOC ) and fill factor (FF), and retained 84% of its initial PCE after 1900h at 65°C in N2 atmosphere. Amazingly, the MAPS-based semi-transparent PSC (STP-PSC) retained 94% of their maximum power (21.00% at around 10% AVT) after 1000h under 1 sun illumination and MAPS-based perovskite submodule (PSM) achieved a PCE of 19.59%, which is among the highest values reported recently.

Suppressed charge recombination via defect engineering of confined semiconducting quantum dots for photoelectrocatalysis.

Confined semiconducting CuSe quantum dots with abundant Se vacancies are synthesized by pulsed laser deposition with in situ vacuum annealing. With the presence of Se vacancies, the photogenerated charge recombination is suppressed by the self-introduced in-gap trapping states, thus enhancing the photoelectrocatalytic activity under solar illumination.

Low-Cost Fully Non-fused Ring Acceptor Enables Efficient Organic Photovoltaic Modules for Multi-Scene Applications.

Organic photovoltaic (OPV) cells, with highly tunable light-response ranges, offer significant potential for use in driving low-power consumption off-grid electronics in multi-scenarios. However, development of photoactive layer materials that can meet simultaneously the requirements of diverse irradiation conditions is a still challenging task. Herein, a low-cost fully non-fused acceptor (denoted as GS60) featuring well-matched absorption spectra with solar, scattered light and artificial light radiation was designed and synthesized. Systematic characterizations revealed that GS60 possessed outstanding photoelectron properties and ideal morphology, which resulted in reduced voltage loss and suppressed charge recombination. By blending with a non-fused ring polymer PTVT-T, the as-obtained GS60 based OPV cells achieved a good power conversion efficiency (PCE) of 14.1 %, a high value for the cells based on non-fused ring bulk heterojunction. Besides, manufactured large-area OPV modules based on PTVT-T:GS60 yielded PCEs of 11.2 %, 11.8 %, 12.1 %, 23.1 %, and 20.3 % under irradiation of AM 1.5G, natural light of cloudy weather, natural light in shadow, laser and indoor, respectively. The PTVT-T:GS60 devices exhibited considerable potential in terms of improving photostability and reducing material cost. Overall, this work provides novel insight into the molecular design of low-cost non-fused ring acceptors, and extended potential of medium band gap acceptors based OPV cells used in various application scenarios.

Low‐Cost Fully Non‐fused Ring Acceptor Enables Efficient Organic Photovoltaic Modules for Multi‐Scene Applications

AbstractOrganic photovoltaic (OPV) cells, with highly tunable light‐response ranges, offer significant potential for use in driving low‐power consumption off‐grid electronics in multi‐scenarios. However, development of photoactive layer materials that can meet simultaneously the requirements of diverse irradiation conditions is a still challenging task. Herein, a low‐cost fully non‐fused acceptor (denoted as GS60) featuring well‐matched absorption spectra with solar, scattered light and artificial light radiation was designed and synthesized. Systematic characterizations revealed that GS60 possessed outstanding photoelectron properties and ideal morphology, which resulted in reduced voltage loss and suppressed charge recombination. By blending with a non‐fused ring polymer PTVT−T, the as‐obtained GS60 based OPV cells achieved a good power conversion efficiency (PCE) of 14.1 %, a high value for the cells based on non‐fused ring bulk heterojunction. Besides, manufactured large‐area OPV modules based on PTVT−T:GS60 yielded PCEs of 11.2 %, 11.8 %, 12.1 %, 23.1 %, and 20.3 % under irradiation of AM 1.5G, natural light of cloudy weather, natural light in shadow, laser and indoor, respectively. The PTVT−T:GS60 devices exhibited considerable potential in terms of improving photostability and reducing material cost. Overall, this work provides novel insight into the molecular design of low‐cost non‐fused ring acceptors, and extended potential of medium band gap acceptors based OPV cells used in various application scenarios.

Auxiliary sequential deposition enables 19%-efficiency organic solar cells processed from halogen-free solvents

High-efficiency organic solar cells are often achieved using toxic halogenated solvents and additives that are constrained in organic solar cells industry. Therefore, it is important to develop materials or processing methods that enabled highly efficient organic solar cells processed by halogen free solvents. In this paper, we report an innovative processing method named auxiliary sequential deposition that enables 19%-efficiency organic solar cells processed by halogen free solvents. Our auxiliary sequential deposition method is different from the conventional blend casting or sequential deposition methods in that it involves an additional casting of dithieno[3,2-b:2’,3’-d]thiophene between the sequential depositions of the donor (D18-Cl) and acceptor (L8-BO) layers. The auxiliary sequential deposition method enables dramatic performance enhancement from 15% to over 18% compared to the blend casting and sequential deposition methods. Furthermore, by incorporating a branched-chain-engineered acceptor called L8-BO-X, device performance can be boosted to over 19% due to increased intermolecular packing, representing top-tier values for green-solvent processed organic solar cells. Comprehensive morphological and time-resolved characterizations reveal that the superior blend morphology achieved through the auxiliary sequential deposition method promotes charge generation while simultaneously suppressing charge recombination. This research underscores the potential of the auxiliary sequential deposition method for fabricating highly efficient organic solar cells using environmentally friendly solvents.

Visible light photoredox catalysis for the synthesis of new chromophores as co-sensitizers with benchmark N719 for highly efficient DSSCs

Dye-sensitized solar cells (DSSCs) are becoming increasingly popular as low-cost organic photovoltaic devices due to their ease of fabrication and affordability. However, a primary limitation of DSSCs is their inability to absorb the entire solar spectrum, leading to lower efficiency. To overcome this limitation, a study was conducted to investigate the use of co-sensitization with two dyes that absorb different wavelengths of light to enhance the overall light absorption. In this study, four novel donor-acceptor (D-A) dyes (5a-d) containing benzo-1,4-diazine or benzo-1,4-oxazine groups as donors and a carbonyl group as an anchor were synthesized using a green and sustainable method to be used as co-sensitizers in DSSCs. These photosensitizers were co-sensitized with the Ru(II) dye N719 and were observed to significantly improve the light-harvesting ability of the device. The co-sensitizers (5a-d) reduced charge recombination, inhibiting dye aggregation, and increased dye loading on the TiO2 photoanode, leading to improve the overall device performance because of the appropriate molecular volume structures of (5a-d), which can fill the adsorption gap between N719 dye. The DSSC device of N719 showed a power conversion efficiency (PCE) of 7.81 % (JSC = 19.06 mA cm−2, VOC = 0.65 V, and FF = 61.24%). After co-sensitization, the PCE and short-circuit current of the device were significantly improved to reach (PCE = 8.79, JSC = 22.89 mA cm−2 and VOC = 0.68 V for 5a), (PCE = 8.56%, JSC = 22.37 mA cm−2, and VOC = 0.68 V mA cm−2 for 5b), (PCE = 8.59%, JSC = 22.45 mA cm−2, and VOC = 0.67 V for 5c) and (PCE = 8.50%, JSC = 21.93 mA cm−2, and VOC = 0.67 V for 5d). These findings demonstrate that co-sensitization with these novel dyes can compensate for the absorption defects of the Ru(II) dye and suppress charge recombination, leading to enhanced overall PCE in DSSCs.

A Biphase Tandem Redox Electrolyte for Efficient Quantum Dot‐Sensitized Solar Cell

A new biphase tandem redox electrolyte system is designed by immobilizing imidazolium iodide on Co, N‐doped carbon electrode in conjunction with polysulfide redox mediator in aqueous solution. Due to its biphasic feature, this redox system is enabled to separate the redox reactions in different phases, and hence, prevent the intertwined problem of redox reactions that occurred in one‐phase tandem redox system. Investigations show that the biphase redox system can efficiently accelerate electron reduction, and thereby inhibit charge recombination. Consequently, quantum dot (QD)‐sensitized solar cell fabricates using this biphase tandem redox together with CdSe QD‐sensitized photoanode achieved a high cell efficiency of 6.85% at 100 mW cm2 simulated AM 1.5, showing about 33% increment as compared to the traditional pure polysulfide‐based device (5.14%). The encouraging results indicate that the utilization of biphase tandem electrolytes can be an efficient way to improve the performance of sensitized solar cells.

Solid-state magic: How Bi2O3 and V2O5 combine to create a high-performance photoanode for water oxidation

A simple method to create a BiVO4–V2O5 photoanode with excellent interfacial contact and self-doping with V4+ and oxygen vacancies was proposed in this study. Direct generation of BiVO4 within the film through a solid state reaction between Bi2O3 and V2O5 was achieved, resulting in a highly efficient charge separation and a photocurrent density of 6.6 mA cm−2 at 1.23 V vs. RHE. The bulk charge separation efficiency was 95 %. This study highlights the importance of good interfacial contact for suppressing charge recombination and enabling efficient water oxidation. The developed synthesis method can be a practical approach for fabricating advanced photoelectrodes for sustainable water-splitting technologies, enabling carbon-free fuel production.

Doping engineering of ZnO electron transporting layer for high performance CsPbI2Br inorganic perovskite solar cells

An inorganic CsPbI2Br perovskite has garnered significant interest due to its outstanding photoelectrical properties in recent years. However, CsPbI2Br-based perovskite solar cells (PSCs) generally suffer from large energy loss, hindering their further development. Herein, we proposed a facile and effective approach to dope the ZnO electron transporting layer (ETL) with alkaline earth metal ions to boost the photovoltaic performance of CsPbI2Br PSCs. Particularly, the ZnO ETL doped with Ca2+ can simultaneously ameliorate electron transport, energy level alignment, and the quality of the upper CsPbI2Br film, thus resulting in faster charge extraction and suppressed charge recombination. Consequently, the ZnO:Ca-based PSC achieves a champion power conversion efficiency (PCE) of 16.39% with an excellent VOC of 1.292 V, while the control ZnO-based PSC just exhibits an inferior PCE of 14.22% with a VOC of 1.178 V. Furthermore, the ZnO:Ca-based devices also present considerable enhancements in device stability without encapsulation. Our work offers a promising strategy to mitigate the energy loss toward efficient and stable PSCs.

Surfactant-free synthesis of AgGO and subsequent catalytic performance of AgGO and WO3-x/AgrGO composites

Suppressing charge recombination in semiconductors via triggering interfacial polarization and synergism provides an effective way to redeem multifunctionality and achieve environmental sustainability. Herein, we anchor a single-step facile synthesis of AgGO, providing bandgap control through varying oxidation time and subsequent simultaneous incorporation of Ag and rGO via the in situ hydrothermal method in WO3-x. The resulting WO3-x/AgrGO composite demonstrated a broadening of optical absorption and excellent suppression of carrier recombination, thereby improving the catalytic properties. The synergism and excellent conductivity of AgrGO enhance the interfacial polarization to store the carriers for longer times and help carriers carry most of their energy to the catalyst’s surface. When WO3-x/AgrGO was tested against RhB under visible light irradiation, its degradation constant reached 0.034/min, 7.4 times faster than pure WO3-x. It has left no viable bacteria during the photoinactivation of gram-negative E. coli bacteria, and even its inactivation rate is 1.07 times faster than AgGO. So, this study provides a direct method of metal-GO composite synthesis and subsequent introduction into WO3-x to broaden the versatility of environmental semiconductors.

Photothermal effect act as controllable switch for tunable photocatalytic selective oxidation of 5-Hydroxymethylfurfural

The selective oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-dicarbofuran (DFF), and 2,5-furanedicarboxylic acid (FDCA) is essential to its practical application. Herein, a novel Pt/ZIS/MnO2 (PMZIS) photocatalysts with photothermal effect were well designed for selective and controlled oxidation of HMF toward DFF or FDCA. The product distribution of HMF photo-oxidation on PMZIS can be regulated by the photothermal effect. At a low temperature (10 °C) with PMZIS, DFF is the primary oxidation product with the yield of 54.6% and selectivity of 85.4%. At a high temperature (60–70 °C) induced by photothermal effect, the FDCA can be obtained with the yield of 61.5 % and selectivity of 82.9%. Moreover, the Z-scheme transfer pathway and Pt cocatalysts realize the spatial charge separation structure of PMZIS heterojunctions. This unique structure greatly inhibits charge recombination and maximizes the activation ability of molecular oxygen to efficiently generate of the reactive oxygen species (e.g., 1O2 and O2–), thus significantly improving the photocatalytic performance. This work would provide valuable insight in the product regulation through photothermal effect for the photocatalytic specific selective oxidation of organic molecules.

Preparation of a flexible photoanode of the photoelectrochemical ultraviolet photodetector based on rutile TiO2 nanowires and the suppressed charge recombination at solid/liquid interface

Flexible ultraviolet (UV) photodetector exhibits a promising application in portable electronic gadgets, display devices and biomedical imaging. In this study, a flexible photoanode of the photoelectrochemical (PEC)-type UV photodetector based on rutile TiO2 nanowires (TiO2 NWs) grown on carbon fiber cloth is realized. In photovoltaic applications, an insulating layer is usually introduced to suppress interfacial recombination and reduce the surface trap states. The interfacial recombination of semiconductor/electrolyte is suppressed by coating an Al2O3 barrier layer on the TiO2 NWs. The photodetectors of the TiO2@Al2O3 NWs show stable photocurrent, a high light/dark current ratio (I light/I dark) of 1170, a faster rise and decay response times of 0.09 and 0.09 s, and excellent spectral selectivity from 300 to 400 nm. The peak responsivity of the photodetectors reaches 2.8 mA W−1 at 360 nm. This flexible photoanode have a potential application in wearable PEC UV photodetector.

Design of benzotriazole-based A2-A1-D-A1-A2-type fully non-fused non-fullerene acceptors for P3HT

Designing fitted acceptors for the homopolymer poly(3-hexylthiophene) (P3HT) has been a hot topic in research field of organic solar cells (OSCs) because of its unique advantages of low-cost, stability and simplicity of synthesis. In resent years, we have been committed to the development of fused non-fullerene acceptors (NFA) containing benzotriazole (BTA) unit in order to achieve high power conversion efficiency (PCE). The modulation of the crystallinity of P3HT in the active layer affecting exciton dissociation, charge transfer and recombination has always been a challenge. Here, two simple non-fused NFAs containing BTA with different terminal units were easily prepared. P3HT:BTA31 device delivered an initial PCE of 3.95 % due to the unbalanced charge mobility and adverse trap-assisted recombination. Due to the efficient charge separation and suppressed charge recombination, P3HT:BTA33 device showed an increased PCE of 5.68 %. Our results suggest that these non-fused NFAs are promising candidates for application of P3HT-based OSCs.

Dual Optimization of Interface Defects and Hole Transporting Layers with Tetrathiafulvalene Derivatives for Antimony Selenosulfide Solar Cells

Modification of hole transporting layers (HTLs) to reduce the interface defects is an important strategy to promote hole extraction and suppress charge recombination for Sb2(S,Se)3 (antimony selenosulfide) solar cells. Herein, a simple doping method with the tetrathiafulvalene derivatives (MeS‐TTF and Cyano‐TTF) is developed to reduce the dangling bonding defects on the surface of Sb2(S,Se)3 films and improve the photovoltaic performances of Sb2(S,Se)3 solar cells. The studies show that the tetrathiafulvalene derivatives can effectively passivate the ionic defects through the chelation mechanism with Sb atoms and suppress the nonradiative recombination. Meanwhile, the MeS‐TTF dopant can also enhance the hole mobility of HTLs and improve the hole transport. The results indicate that the MeS‐TTF can achieve the dual function of interface defect passivation and hole mobility improvement. As a result of the dual‐function dopant, a significant increase in efficiency from 7.73% to 8.45% can be obtained. The outcomes of this study highlight that this dual‐function doping strategy is an effective method to passivate the interface defects and enhance the hole mobility for the excellent photovoltaic performances of Sb2(S,Se)3 solar cells.

Enhanced ZnO-based ETL and nanostructured interface modification for improved perovskite solar cells efficiency

Compared to standard silicon solar cells and other thin film cells, perovskite solar cells (PSCs) can achieve high power conversion efficiency and reduce the production costs. ZnO-based ETL in perovskite solar cells provides a lot of benefits, such as low processing temperature and high mobility. However, the reported instability of perovskite layers placed atop ZnO, resulting in poor device performance, has prevented it from being widely used in perovskite solar cells, though. In this work, an innovative way of insuring device performance and longer-term stability is proposed via the incorporation of a novel efficient process. Herein, a V-doped ZnO/Y-doped TiO2 electron transport bilayer was developed to combine the benefits of strong electron extraction and minimal interfacial recombination. This combined approach of engineering both the improved performance of VZnO as ETL and YTiO2 flower like structures at the interface ETL/Perovskite results in large improvements in the performance of the PSC. V-doped ZnO (VZnO) was introduced into the PSC structure as an ETL, due to its excellent electrical and optical properties, to improve electron extraction efficiency, with a doping amount of 4 at.% of vanadium. The latter has been optimized in our previous study. On the other hand, extrinsically doping TiO2 with an amount of 5 at.% of Yttrium (YTiO2) was utilized to enhance its physicochemical properties. The PSC based on VZnO/YTiO2 bilayer ETL possess the best PCE of 15.1%, compared to 9.4% in the pristine ZnO-based ETL solar cell, with the open-circuit voltage (Voc) of 923 mV, short-circuit photocurrent density (Jsc) of 22 mA cm−2, and fill factor (FF) of 74%. Obtained improvements are ascribed to the suppressed charge recombination via the incorporation of YTiO2 flower-like nanostructures at the interface VZnO/perovskite and the enhanced electron transporting in the resulting ETL bilayer structure.

High Detectivity Near Infrared Organic Photodetectors Using an Asymmetric Non-Fullerene Acceptor for Optimal Nanomorphology and Suppressed Dark Current.

Recently, the development of non-fullerene acceptors (NFAs) for near-infrared (NIR) organic photodetectors (OPDs) has attracted great interest due to their excellent NIR light absorption properties. Herein, we developed NFAs by substituting an electron-donating moiety (branched alkoxy thiophene (BAT)) asymmetrically (YOR1) and symmetrically (YOR2) for the Y6 framework. YOR1 exhibited nanoscale phase separation in a film blended with PTB7-Th. Moreover, substituting the BAT unit effectively extended the absorption wavelengths of YOR1 over 1000 nm by efficient intramolecular charge transfer and extension of the conjugation length. Consequently, YOR1-OPD exhibited significantly reduced dark current and improved responsivity by simultaneously satisfying optimal nanomorphology and significant suppression of charge recombination, resulting in 1.98 × 1013 and 3.38 × 1012 Jones specific detectivity at 950 and 1000 nm, respectively. Moreover, we successfully demonstrated the application of YOR1-OPD in highly sensitive photoplethysmography sensors using NIR light. This study suggests a strategic approach for boosting the overall performance of NIR OPDs targeting a 1000 nm light signal using an all-in-one (optimal morphology, suppressed dark current, and extended NIR absorption wavelength) NFA.

Morphology Control for Efficient Nonfused Acceptor-Based Organic Photovoltaic Cells.

Non-fused electron acceptors have huge advantages in fabricating low-cost organic photovoltaic (OPV) cells. However, morphology control is a challenge as non-fused C─C single bonds bring more molecular conformations. Here, by selecting two typical polymer donors, PBDB-TF and PBQx-TF, the blend morphologies and its impacts on the power conversion efficiencies (PCEs) of non-fused acceptor-based OPV cells are studied. A selenium-containing non-fused acceptor named ASe-5 is designed. The results suggest that PBQx-TF has a lower miscibility with ASe-5 when compared with PBDB-TF. Additionally, the polymer networks may form earlier in the PBQx-TF:ASe-5 blend film due to stronger preaggregation performance, leading to a more obvious phase separation. The PBQx-TF:ASe-5 blend film shows faster charge transfer and suppressed charge recombination. As a result, the PBQx-TF:ASe-5-based device records a good PCE of 14.7% with a higher fill factor (FF) of 0.744, while the PBDB-TF:ASe-5-based device only obtains a moderate PCE of 12.3% with a relatively low FF of 0.662. The work demonstrates that the selection of donors plays a crucial role in controlling the blend morphology and thus improving the PCEs of non-fused acceptor-based OPV cells.

Nanomaterials for Advanced Photocatalytic Plastic Conversion.

As the disposal of waste plastic emerges as a societal problem, photocatalytic waste plastic conversion is attracting significant attention. Ultimately, for a sustainable future, the development of an eco-friendly plastic conversion technology is essential for breaking away from the current plastic use environment. Compared to conventional methods, photocatalysis can be a more environmentally friendly option for waste plastic reprocessing because it uses sunlight as an energy source under ambient temperature and pressure. In addition to this, waste plastics can be upcycled (i.e., converted into useful chemicals or fuels) to enhance their original value via photocatalytic methods. Among various strategies for improving the efficiency of the photocatalytic method, nanomaterials have played a pivotal role in suppressing charge recombination. Hence, in recent years, attempts have been made to introduce nanomaterials/nanostructures into photocatalytic plastic conversion on the basis of advances in material-based studies using simple photocatalysts. In line with this trend, the present review examines the nanomaterials/nanostructures that have been recently developed for photocatalytic plastic conversion and discusses the direction of future development.

Recent Progresses on Dopant‐Free Organic Hole Transport Materials toward Efficient and Stable Perovskite Solar Cells†

Comprehensive SummaryAs the third generation new battery, the power conversion efficiency (PCE) of metal halide perovskite solar cells (PSCs) has increased from 3.8% in 2009 to 25.8% currently certified, which fully shows that they have great research value and development prospect. As one of the main components of high‐efficiency PSCs, hole transport materials (HTMs) play an important role in extracting and transporting holes and inhibiting charge recombination. However, commonly used HTMs require doping, and the hygroscopicity and corrosiveness of the dopants will destroy the stability of PSCs and hinder their commercialization. Therefore, it is of great significance to develop dopant‐free HTMs. In this review, the dopant‐free HTMs in recent six years are reviewed and summarized systematically, including organic small molecules, polymers and cross‐linkable materials. We focus on the design of the molecular cores and discuss their structure–property correlation, conductivity, and photovoltaic performance. Finally, how to design an ideal HTM is summarized. We hope that this review can provide reference for the development of low‐cost and dopant‐free HTMs to prepare efficient and stable PSCs.

Spatial charge separated two-dimensional/two-dimensional Cu-In2S3/CdS heterojunction for boosting photocatalytic hydrogen production

Two-dimensional (2D) beta indium sulfide (β-In2S3) shows great potential in photocatalytic hydrogen production due to its broad-spectrum response, relatively negative conduction band edge, high carrier mobility and low toxicity. However, the high charge recombination rate limits the application of In2S3. Here, we in-situ grew 2D cadmium sulfide (CdS) on the surface of In2S3 doped with copper ions (Cu2+) to construct a heterojunction photocatalyst that suppresses charge recombination. The in-situ grown method and shared sulfur composition were conducive to forming the efficient interface contact between In2S3 and CdS, promoting charge transfer and showing the high spatial charge separation rate, resulting in a hydrogen production rate of 868 µmol g-1h−1. The induced Cu2+ extended the light absorption range and stabilized the photocatalyst. By creating stable 2D/2D heterojunction photocatalysts with high charge separation efficiency, this work opens new possibilities for applying In2S3 materials in photocatalytic hydrogen production.