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Single-crystalline CeO2−x hollow nanorods possess more Ce3+ states and wider surface area than other types of cerium oxide nanostructures and those enable the resultant organic photovoltaic cells to have improved photostability.

Developing intrinsically self-healable semiconducting polymers is particularly important for realizing stretchable electronic devices which can spontaneously recover their mechanical damage. We synthesized a series of conjugated donor polymers (PTO2-tm series) functionalized with a thymine group at the terminal of the side chain. Bulk heterojunction (BHJ) films of PTO2-tm polymers blended with an IT-4F acceptor achieved power conversion efficiencies up to 11.9% from the BHJ-based organic photovoltaics, which are comparable with that of unfunctionalized PTO2 and, however, exhibited much improved stretchability by virtue of stress dissipation in the BHJ films during mechanical deformation. More importantly, the corresponding BHJ film prepared with a melamine additive efficiently recovered their packing structures after being mechanically damaged by stretching. As a result, reversible multiple hydrogen bonding of the melamine molecule with thymine in PTO2-tm polymers showed much improved crack onset strain and maximum recoverable strain compared with PTO2.

Purpose Colonoscopy is an effective method of screening for colorectal cancer (CRC), and it can prevent CRC by detection and removal of precancerous lesions. The most important considerations when performing colonoscopy screening are the safety and satisfaction of the patient and the diagnostic accuracy. Accordingly, the Korean Society of Coloproctology (KSCP) herein proposes an optimal level of standard performance to be used in endoscopy units and by individual colonoscopists for screening colonoscopy. These guidelines establish specific criteria for assessment of safety and quality in screening colonoscopy. Methods The Colonoscopy Committee of the KSCP commissioned this Position Statement. Expert gastrointestinal surgeons representing the KSCP reviewed the published evidence to identify acceptable quality indicators and indicators that lacked sufficient evidence. Results The KSCP recommends an optimal standard list for quality control of screening colonoscopy in the following 6 categories: training and competency of the colonoscopist, procedural quality, facilities and equipment, performance indicators and auditable outcomes, disinfection of equipment, and sedation and recovery of the patient. Conclusion The KSCP recommends that endoscopy units performing CRC screening evaluate 6 key performance measures during daily practice.

With the development of nonfullerene acceptors (NFAs), the efficiency of organic photovoltaics (OPVs) has been remarkably improved and exceeded 18%. The morphology of bulk heterojunction films (BHJs) importantly affects all individual steps of exciton generation and charge separation and transport. Although many solution processing techniques developed from fullerene-based systems have been effectively utilized for morphology control of NFA-based BHJs, the optimization process is still complicated due to diverse chemical structures of donor and NFA materials. In addition, it is important to develop materials and processing techniques for reliable transfer of the BHJ morphology realized in small-areas to large-areas. This article reviews mechanisms of morphology evolution of the BHJ film and recent research progress for control of NFA-based BHJs; this includes studies of structure-property relationship of organic materials and processing techniques which have been practically employed for morphology optimization of the NFA blends, such as uses of ternary compositions and solvent additives and post treatments of the BHJ film. Finally, we survey coating techniques for producing scalable BHJs and provide perspectives to realize high-performance OPV devices for practical industrial applications. This review can guide to resolve the morphological issues for new materials to achieve higher efficiency NFA-based OPVs.

We synthesized thienyl-benzodithiophene and ester-substituted thiophene-based conjugated donor polymers (PTO2-urea series) functionalized with a urea group at the terminus of the side chain. When stretched, the prepared polymer film, PTO2-urea10, in which 10 mol% of monomers constituting the polymer are the urea-functionalized monomers, showed increased crystallinity in the in-plane direction of the film. In contrast, the unmodified PTO2 polymer exhibited anisotropic reorientation of polymer crystallites in the same direction. Experiments showed that stretching-induced temporary molecular alignment in the amorphous region of PTO2 recovered to the initial state when the applied strain was removed. In contrast, hydrogen bonding between the urea groups of the polymer alkyl chains effectively maintained the organized polymer packing structures which were induced under applied strain. As a result, whereas a PTO2-based thin film transistor (TFT) device showed a dramatic decrease in hole mobility from 1.0 × 10−2 to 5.6 × 10−3 cm2 V−1 s−1 because of morphological damage and cracking of the PTO2 film, the device with a PTO2-urea10 film maintained a relatively high TFT mobility of 5.8 × 10−3 cm2 V−1 s−1 in the direction perpendicular to the strain direction because of the increased crystallinity of the polymer.

Understanding the effects of the chemical structures of donor polymers on the photovoltaic properties of their corresponding organic photovoltaic (OPV) devices under various light-intensity conditions is important for improving the performance of these devices. We synthesized a series of copolymers based on poly[(2,6-(4,8-bis(5-(2-thioethylhexyl)thiophen-2-yl)benzo[1,2

A new polymeric semiconductor, which can effectively extend linear dynamic ranges (LDRs) of organic photodiodes (OPDs), was developed. Copolymers based on alkylthio-substituted benzo[1,2-b:4,5-b′]d...

Random terpolymers are developed by incorporating small portions of benzodithiophene into a highly crystalline copolymer of terthiophene and difluorobenzothiadiazole, BDT-Th0. The bulk-heterojuncti...

Correction for ‘Crystallinity-modulated hollow CeO2−x nanorods as free radical scavengers for long-term photostability in organic photovoltaics’ by Seongwon Yoon et al., J. Mater. Chem. C, 2023, 11, 970–979, https://doi.org/10.1039/D2TC04152A.

We developed perovskite solar cells (PSCs) with a ZnO electron-transporting layer (ETL) of which the surface was passivated with methoxybenzoic acid self-assembled monolayers (SAMs). The self-assembled monolayer (SAM) simultaneously improved the photovoltaic performance and device stability. First, the methoxybenzoic acid, which is noncovalently bonded to the methylammonium of the perovskite layer, effectively induced dipole moments; in particular, 3,4,5-trimethoxybenzoic acid (TMBA) gave a larger workfunction shift of ZnO ETL compared with 4-methoxybenzoic acid (MBA) and 3,4-dimethoxybenzoic acid (DMBA) owing to its strong dipole moment and hydrogen-bonding between the methoxy group and ammonium. This effectively enhanced the built-in voltage of the perovskite solar cell (PSC) device, which resulted in an improved electron transfer from the active layer to the ETL and a higher open-circuit voltage. Secondly, the SAM layer controlled the wettability of the perovskite precursor solution on the ZnO ETL and significantly improved the crystalline properties of the perovskite layer. Moreover, the ZnO/SAM ETL remarkably increased the PSC device stability under ambient conditions by preventing the proton transfer reaction between the perovskite layer and the ZnO ETL. As a result, the TMBA-SAM based PSC device achieved a significantly enhanced efficiency of 13.75% compared to 1.44% for the bare ZnO with high long-term stability.

We synthesized a donor polymer of bis(2-ethylhexyl)thiophene-substituted benzodithiophene (BDT-Th) and 1,3-bis(2-ethylhexyl)-5,7-di(thiophene-2-yl)benzo[1,2-c:4,5-c′]dithiophene-4,8-dione, for whic...

Charge-transport materials for use in highly efficient and stable perovskite solar cells (PSCs) must exhibit energy levels appropriate for high charge selectivity, sufficiently high charge-transport ability for efficient charge collection, and high humidity resistance for long-term device stability. Polythiophenes are a promising class of hole-transport layer (HTL) materials that could satisfy these requirements. However, PSCs fabricated using conventional poly(3-hexylthiophene) (P3HT) HTLs show limited efficiencies of

Here, we develop a method to prepare a dopant-free hole transporting material by blending an organic semiconductor and a conjugated polymer with 1,8-diiodooctane (DIO) additive. The normal-type solar cell based on the hole transporting material (HTM) blend with DIO + PCDTBT shows enhanced efficiency up to 18.0% compared to 14.7% for the device using the pristine small molecule. Incorporation of DIO results in increased crystallinity, while the conjugated polymer induces an intermolecular network for efficient charge transport with improved film morphology. Consequently, the HTM blend with DIO + PCDTBT shows a higher hole mobility and more efficient charge transfer at the perovskite/hole transporting layer interface compared with the pristine HTM. Furthermore, the solar cell introducing the HTM blend with DIO shows high mechanical and moisture stability; the compact and homogeneous film of high crystalline HTM shows more adhesive contact with perovskite and effectively prevents the penetration of moisture. The efficiency of the unencapsulated device using a small molecular HTM decreases to 60%, whereas the corresponding device with HTM blend maintains 80% performance after storage under 85% relative humidity and 85 °C.

For enhancing the performance and long-term stability of perovskite solar cell (PSC) devices, interfacial engineering between the perovskite and hole-transporting material (HTM) is important. We developed a fluorinated conjugated polymer PFPT3 and used it as an interfacial layer between the perovskite and HTM layers in normal-type PSCs. Interaction of perovskite and PFPT3 via Pb-F bonding effectively induces an interfacial dipole moment, which resulted in energy-level bending; this was favorable for charge transfer and hole extraction at the interface. The PSC device achieved an increased efficiency of 22.00% with an open-circuit voltage of 1.13 V, short-circuit current density of 24.34 mA/cm2, and fill factor of 0.80 from a reverse scan and showed an averaged power conversion efficiency of 21.59%, which was averaged from forward and reverse scans. Furthermore, the device with PFPT3 showed much improved stability under an 85% RH condition because hydrophobic PFPT3 reduced water permeation into the perovskite layer, and more importantly, the enhanced contact adhesion at the PFPT3-mediated perovskite/HTM interface suppressed surface delamination and retarded water intrusion. The fluorinated conjugated polymeric interfacial material is effective for improving not only the efficiency but also the stability of the PSC devices.

The performances of polymer solar cells (PSCs) based on non-fullerene acceptors (NFAs) have improved remarkably in recent years, but such devices are insufficiently stable for practical applications. Here, we investigated the effects of NFAs on PSC long-term stability. We found that high performance PBDB-T : ITIC solar cells exhibit much lower stability than PTB7 : PC71BM devices in the 1 sunlight-soaking test; when compared with their initial performances, the performance of PTB7 : PCBM-based solar cells remains above 60% for over 4000 h, whereas that of PBDB-T : ITIC-based devices is reduced to one fifth after 1000 h. We demonstrated that the ITIC-based PSCs exhibit poor photo-stability because ITIC at the interface of the ZnO/active film is readily decomposed by a photocatalytic reaction; this poor stability arises because the vinyl group of ITIC is chemically more vulnerable than the stable aromatic units in the organic active materials. The decomposition of ITIC results in the degradation of the electron transport properties of the active materials located close to ZnO, which leads to severe burn-in degradation and reduced FF and VOC under illumination. It is thus highly important to develop intrinsically stable organic materials composed of chemically stable building blocks in order to realize stable and high efficiency PSCs.

Organic solar cells based on bulk heterojunctions (BHJs) are attractive energy-conversion devices that can generate electricity from absorbed sunlight by dissociating excitons and collecting charge carriers. Recent breakthroughs attained by development of nonfullerene acceptors result in significant enhancement in power conversion efficiency (PCEs) exceeding 17%. However, most of researches have focused on pursuing high efficiency of small-area (

We report a suitable Li-doped NiOx hole-extraction layer of p–i–n type planar perovskite solar cell as an alternative to organic material such as PEDOT:PSS. The Li-doped NiOx used as hole-extraction layer can be prepared by facile method of just adding Li source to NiOx precursor solution to form Li-doped NiOx layer. The presence of Li in NiOx layer has an influence on conductivity of the NiOx layer which is evidenced by the conductive AFM. In addition, the NiOx layer with 50 nm thickness prevents a lot of pinholes inside the film and relatively low processing temperature of 200 °C has the advantage of wide choice of transparent conduction oxide substrate. As a result, p–i–n type planar perovskite solar cell incorporating the Li-doped NiOx hole-extraction layer is improved with significantly enhanced fill factor leading to increase in conversion efficiency of 15.41%.

The control of the optoelectronic properties of the interlayers of perovskite solar cells (PSCs) is crucial for achieving high photovoltaic performances. Of the solution-processable interlayer candidates, NiOx is considered one of the best inorganic hole-transporting layer (HTL) materials. However, the power conversion efficiencies (PCEs) of NiOx-based PSCs are limited by the unfavorable contact between perovskite layers and NiOx HTLs, the high density of surface trap sites, and the inefficient charge extraction from perovskite photoactive layers to anodes. Here, we introduce a new organic-inorganic double HTL consisting of a Cu:NiOx thin film passivated by a conjugated polyelectrolyte (PhNa-1T) film. This double HTL has a significantly lower pinhole density and forms better contact with perovskite films, which results in enhanced charge extraction. As a result, the PCEs of PSCs fabricated with the double HTL are impressively improved up to 17.0%, which is more than 25% higher than that of the corresponding PSC with a Cu:NiOx HTL. Moreover, PSCs with the double HTLs exhibit similar stabilities under ambient conditions to devices using inorganic Cu:NiOx. Therefore, this organic-inorganic double HTL is a promising interlayer material for high performance PSCs with high air stability.

Nonfullerene acceptors have played a critical role in achieving record efficiency of organic photovoltaic (OPV) devices, and ITIC-based materials are an important type of nonfullerene acceptor. Herein, we developed new interlayer polymers for nonfullerene acceptor-based OPVs: PDMA(N)EMA and PDMA (N–O)EMA. In particular, PDMA(N)EMA effectively lowered the work function at the interface with the bulk heterojunction active layer and thus enabled efficient electron collection by the OPV device. Therefore, the OPV device incorporating PDMA(N)EMA showed a power conversion efficiency (PCE) of 8.19%, which was substantially enhanced compared with the 4.54% PCE of an ethoxylated polyethylenimine (PEIE)-based device. Whereas PEIE chemically attacked ITIC and degraded the performance of the OPV device, the PDMA(N)EMA formed a stable interface with ITIC, resulting in a dramatic increase of the VOC of the PDMA(N)EMA-based devices. Furthermore, the suppression of degradation at the PDMA(N)EMA interface also improved device stability at elevated temperatures. This work highlights the importance of the design and development of appropriate interlayer materials for realizing stable and high-efficiency nonfullerene-based OPVs.

Tandem solar cells which are electrically connected with various photoactive materials have the potential to solve the current challenges by exceeding the theoretically limited efficiency of single junction solar cells. Here the first monolithic organic/silicon tandem cell is reported based on a semitransparent polymer on a crystalline silicon (c-Si) substrate. Herein, experimental results are presented for four-terminal (4-T) and monolithic two-terminal (2-T) organic/c-Si tandem cells using organic cells with an inverted n-i-p structure and c-Si cells with an n-type TOPCon structure with detailed analysis. The best 4-T tandem cell efficiency is 15.22%, and 2-T results show that the top (organic) and bottom (c-Si) cells are electrically connected by an open-circuit voltage over 1.4 V. Further, a simulated efficiency of over 20% using the organic/c-Si tandem is achieved, implying the tandem efficiency can be enhanced through further improvement of electric and optical characteristics with the optimization.

To achieve highly efficient organic photovoltaic (OPV) devices, the interface between the photoactive layer and the electrode must be modified to afford the appropriate alignment of the energy levels and to ensure efficient charge extraction at the same time as suppressing charge recombination and accumulation. Recently, p-type conjugated polyelectrolytes (CPEs) have emerged as new hole-transporting materials that can be deposited on electrodes through simple solution processes without additional heat treatment. However, the applications of CPEs have been limited so far because the high electron richness of their conjugated backbones result in low work functions, ∼5.0 eV. Here, by inserting a donor−acceptor (D−A) building block into the CPE backbone, we successfully synthesized a new p-type CPE (PhNa-DTBT), which shows a deep work function above 5.3 eV on several electrodes including Au, Ag, and indium tin oxide. More importantly, PhNa-DTBT produces stable polarons on the polymer backbone and thus achieves a high electrical conductivity of 5.7 × 10−4 S cm−1. As a result, an OPV incorporating PhNa-DTBT as a hole-transporting layer was found to exhibit a high performance with a power conversion efficiency of 9.29%. Also, the OPV device shows improved stability in air due to the neutral characteristics of the CPE which is favorable for stabilizing neighbored active and electrode layers.

We developed donor–acceptor (D–A)-type random polymers based on 3,3′-difluoro-2,2′-bithiophene with various relative amounts of 5,6-difluoro-4,7-bis(5-bromo-(2-decyltetradecyl)thiophen-2-yl)-2,1,3-benzothiadiazole (2FBT) and 5,6-difluoro-4,7-bis(5-bromo-(2-octyldodecyl)thiophen-2-yl)-2-(3,4-dichlorobenzyloxybutyl)-2H-benzo[d][1,2,3]triazole (DCB-2FBTZ). Introducing small relative amounts of DCB-2FBTZ into the polymer was found to effectively enhance its solar cell performance, resulting in a power conversion efficiency of 9.02%, greater than the 7.29% that resulted from the PFBT-FTh copolymer. Moreover, when the active area of the BHJ film was increased to 1 cm2, the solar cell reproducibly showed a high performance, here with an efficiency of 8.01% even when the thickness of the active layer was 313 nm. Our studies revealed that including the DCB-2FBTZ group in the polymer simultaneously improved the solution processability and crystallinity of the polymer. These improvements resulted in the formation of...

A series of novel conjugated polyelectrolytes composed of two different building blocks with different composition ratios were designed and synthesized for application as a functional layer in high-performance organic photodiodes (OPDs). A homopolymer and two random copolymers were prepared using different molar ratios of dibromo 1,4-bis(4-sulfonatobutoxy)benzene (SPh) and dibromo 1,4-bis(4-tetraethylene glycol)benzene (EGPh): EG20 with SPh:EGPh ratio of 0.8:0.2 and EG40 with a ratio of 0.6:0.4. Structural analyses by two-dimensional grazing-incidence X-ray diffraction and near-edge X-ray absorption fine structure spectroscopy studies proved that a higher EGPh content could induce more organized polymer chains with face-on orientation of EG20 and EG40. Such an orientation of EG20 and EG40 along with the ordered crystalline organization yielded effective molecular dipole moments in the thin films when applied as an interlayer between ZnO and an active layer of inverted OPDs. As confirmed by ultraviolet pho...

Understanding the role of appended alkyl side chains is a key issue to enhance photovoltaic performance because the side chains control molecular solubility, film crystallinity, and morphology. For this purpose, we synthesized three new planar aromatic backbone molecules ( Eh-Hex , Eh-Eh and Oct-Eh ), where the appended alkyl side chains on the aromatic core unit were either 2-ethylhexyl (Eh) or n-octyl (Oct) and those on the side ends were either Eh or hexyl (Hex). Characterization of the molecular films revealed that all of the molecules were crystalline with mainly edge-on orientation, while the Eh-Hex and Eh-Eh molecules having Eh groups on the core units manifested higher crystallinity than the molecule ( Oct-Eh ) having Oct groups on the core units. Of the small molecule:PC 71 BM blend films, only the Eh-Hex case exhibited both good intermolecular packing and uniformly distributed nanoscopic networks of molecular channels, maintaining extensive interfacial contacts between the Eh-Hex and PC 71 BM domains. On the other hand, the Eh-Eh molecules showed poor miscibility with PC 71 BM, and the Oct-Eh molecules displayed excessive miscibility with PC 71 BM. These morphological differences resulted in significant differences in the photovoltaic performance of the devices using small molecule:PC 71 BM blend films. Inverted-type photovoltaic devices fabricated using the Eh-Hex :PC 71 BM blend had the highest power conversion efficiency among the three molecule-based devices. Overall, this work demonstrated that both the type of alkyl side chain and its position are crucial factors controlling the balance of interactions between small molecules and PC 71 BM molecules, which can significantly alter blend morphology and photovoltaic performance.

Stretchability and areal coverage of active devices are critical design considerations of stretchable or wearable photovoltaics and photodetections where high areal coverages are required. However, simultaneously maximizing both properties in conventional island-bridge structures through traditional two-dimensional manufacturing processes is difficult due to their inherent trade-offs. Here, a 3D printer-based strategy to achieve extreme system stretchability and high areal coverage through combining fused deposition modeling (FDM) and flexible conductive nanocomposites is reported. Distinguished from typical approaches of using conductive filaments for FDM which have a flexibility dilemma and conductivity trade-offs, the proposed axiomatic approach to embed a two-dimensional silver nanowire percolation network into the surfaces of flexible 3D printed structures offers sufficient conductivity and deformability as well as additional benefits of electrical junction enhancement and encapsulation of silver nanowires. Kirigami/origami-pattern-guided three-dimensional arrangements of encapsulated interconnections provide efficient control over stretchability and areal coverage. The suggested process enables a perovskite solar module with an initial areal coverage of ∼97% to be electrically and mechanically reversible with 400% system stretchability and 25 000% interconnect stretchability under the 1000 cycle test, by folding down or hiding the origami-applied interconnects under the islands. This 3D printing strategy of potentially low cost, large size capabilities, and high speed is promising for highly flexible future energy conversion applications.

We synthesized a planar pDPPTTi-OD polymer based on diketopyrrolopyrrole (DPP) and thieno [2,3- b ]thiophene (TTi) and investigated the electrical properties of the pDPPTTi-OD polymer. pDPPTTi-OD films displayed a low optical bandgap of 1.57 eV, and HOMO and LUMO levels of −5.40 and −3.74 eV, respectively. The 150°C-annealed pDPPTTi-OD films showed a high hole mobility of 0.16 cm 2 V −1 s −1 in organic thin-film transistor (OTFT) devices. The photovoltaic properties of polymer solar cells (PSCs) incorporating the pDPPTTi-OD were also measured. A pDPPTTi-OD:PC 71 BM blend film was spin-coated at 25, 70 and 90 °C. High-temperature processing significantly improved the power conversion efficiency of PSCs by effectively reducing the PC 71 BM domain sizes, which improved the miscibility between pDPPTTi-OD and PC 71 BM. This work demonstrated that the TTi moiety is a useful donor building block for high- performance D–A type polymers in OTFTs and PSCs, and that processing temperatures should be controlled to fully realize the materials' beneficial intrinsic properties.

The photostability of donor–acceptor (D–A) polymers remains a critical issue despite recent improvements in the power conversion efficiencies (PCEs) of organic photovoltaic (OPV) cells. We report the synthesis of three highly photostable polymers (PDTBDT-BZ, PDTBDT-BZF, and PDTBDT-BZF2) and their suitability for use in high-performance OPV cells. Under 1 sunlight of illumination in air for 10 h, these polymer films demonstrated remarkably high photostability compared to that of PTB7, a representative polymer in the OPV field. While the PDTBDT-BZ, PDTBDT-BZF, and PDTBDT-BZF2 polymer films maintained 97, 90, and 96% photostability, respectively, a PTB7 film exhibited only 38% photostability under the same conditions. We ascribed the high photostability of the polymers to both the intrinsically photostable chemical moieties and the dense packing of alkyl side chains and planar backbone polymer chains, which prevents oxygen diffusion into the PDTBDT-BZ films. This work demonstrates the high photostability of ...

Molybdenum disulfide (MoS 2 ) is a promising material for use as a low-cost electrocatalytic counter electrode (CE) in photoelectrochemical dye-sensitized solar cells (DSSCs). However, currently, the MoS 2 CEs are generally prepared with a high temperature sintering for the synthesis and crystallization of MoS 2 . Here, we report a simple and rapid method for the preparation of highly efficient MoS 2 CEs. The MoS 2 films were synthesized at 70 °C, followed by sintering with a near-infrared (IR) pulsed laser for 1 min. Compared to the conventional heat-sintered MoS 2 CE, the laser-sintered CE showed enhanced crystallinity and improved interconnection between the MoS 2 particles, resulting in superior electrocatalytic activity towards the I − /I 3 − redox couple. When used in a DSSC, the laser-sintered MoS 2 CE exhibited a higher conversion efficiency ( η = 7.19%) compared to that of the heat-sintered CE ( η = 5.96%). Furthermore, the laser-sintered CE had a comparable conversion efficiency compared to that of the conventional Pt CE ( η = 7.42%).

To realize high-performance flexible perovskite solar cells (PSCs), electron selective layers (ESL) that can be processed at low temperatures are required. Here, we develop UV-assisted solution process to prepare highly compact Nb-doped TiO2 (UV-Nb:TiO2) ESLs at low temperature (

Because large amounts of solvents are needed for large-scale fabrication of organic solar cells, it is important to develop solar cell processes using environmentally friendly solvents. In the research, we introduce a new approach to control the morphology of polymer:PC 71 BM blend films by an additive-free and non-halogenated solvent system. Incorporation of a fullerene-compatible o -dichlorobenzene group as the side chain of polythienothiophene-co-benzodithiophene derivatives importantly enhances the compatibility of the polymer with PC 71 BM and improves the nano-scale morphology of the blend film processed from o -xylene. We studied the effect of introducing the o -dichlorobenzene group onto the polymer on the morphology, charge mobility, and solar cell performances as comparing the cases of the polymer before modification. The developed polymer:PC 71 BM-based solar cells prepared using o -xylene show a remarkably improved performance with a PCE of 6.07%.

Highly crumpled graphene-based three dimensional (3D) interconnected and hierarchically porous conducting networks were prepared for application as electrocatalytic counter electrode (CE) in dye-sensitized solar cells (DSSCs). Finely and hierarchically crumpled graphene was synthesized from Fe 2 O 3 /graphene oxide (GO) hybrids via a one-step chemical etching–reduction process with HI solution. The synthesized crumpled graphene exhibited not only 24 times higher specific surface area, but also superior dispersibility in aqueous solution compared to conventional reduced graphene oxide (rGO). Owing to its superior solution processability and comparable electrical conductivity, the crumpled graphene could be assembled into 3D interconnected films on the substrates simply by drop casting, without any binders. In addition, although the crumpled graphene was not modified by dopants or high-temperature annealing, it showed much higher electrocatalytic activity for the I − /I 3 − redox couple compared to that of rGO, which is mainly attributed to its significantly larger accessible surface area for electrochemical reduction. As a result, the DSSC containing the crumpled graphene CE exhibited 2.8 times enhanced conversion efficiency (η = 5.15%) compared to that containing a rGO electrode (η = 1.86%).

Lead halide perovskite solar cells (PSCs) are thought to be promising energy power suppliers because of their feasibility for high power conversion efficiency (PCE), light weight, and flexible architecture. The preparation of charge transporting layers at low temperature has been essential for high-performance and flexible PSCs. Recently, low-temperature-processed metal oxides have been a desirable material for charge transport and air stability for PSCs, instead of organic semiconductors. However, pristine metal oxides fabricated at low temperature have still precluded high performance of the device because of their low conductivity and large deviation in energy levels from the conduction band or valance band of the perovskite. Therefore, doping metals in the metal oxides has been considered as an effective method to endow suitable electrical properties. Herein, we developed a highly efficient electron transporting layer (ETL) comprising Li-doped SnO2 (Li:SnO2) prepared at low temperature in solution. The doped Li in SnO2 enhanced conductivity as well as induced a downward shift of the conduction band minimum of SnO2, which facilitated injection and transfer of electrons from the conduction band of the perovskite. The PCE was measured to be 18.2% and 14.78% for the rigid and flexible substrates, respectively. The high-performance and flexible PSCs could be potentially used as a wearable energy power source.

Here we report the effects of iodine doping on small molecule organic semiconductors. Thin films of semiconducting p-DTS(FBTTh2)2 doped with 1–5 wt% iodine were fabricated and their photo-physical, crystallographic, morphological, and electrical properties were systematically analyzed. The doping significantly increased the energetic distance between the highest occupied molecular orbital (HOMO) and Fermi level of p-DTS(FBTTh2)2, typical for p-type doping. In addition, depletion mode transistor measurements showed an increase in the hole concentration with increasing dopant concentration. From grazing incidence X-ray diffraction (GIXD) analyses of iodine-doped p-DTS(FBTTh2)2 films, we observed significant changes in the crystal orientation at the optimal doping ratio of 1 wt%. Atomic force microscopy (AFM) analyses showed morphological changes with respect to dopant concentrations, which were in good agreement with the GIXD results. As a result, accumulation mode transistor measurements demonstrated an increase in the hole mobility by 54% at the optimized doping concentration compared to an undoped device. Furthermore, photoconductive device operation revealed that iodine-doping can induce dramatically enhanced photo-responsivity as high as 2.08 A/W. We demonstrate that iodine doping can be a simple and effective method for enhancing the performance of small molecule-based electronic devices, by optimizing the energy level configuration as well as enhancing intermolecular interactions.

Organo-lead halide perovskite solar cells (PSCs) have received great attention because of their optimized optical and electrical properties for solar cell applications. Recently, a dramatic increase in the photovoltaic performance of PSCs with organic hole transport materials (HTMs) has been reported. However, as of now, future commercialization can be hampered because the stability of PSCs with organic HTM has not been guaranteed for long periods under conventional working conditions, including moist conditions. Furthermore, conventional organic HTMs are normally expensive because material synthesis and purification are complicated. It is herein reported, for the first time, octadecylamine-capped pyrite nanoparticles (ODA-FeS2 NPs) as a bi-functional layer (charge extraction layer and moisture-proof layer) for organo-lead halide PSCs. FeS2 is a promising candidate for the HTM of PSCs because of its high conductivity and suitable energy levels for hole extraction. A bi-functional layer based on ODA-FeS2 NPs shows excellent hole transport ability and moisture-proof performance. Through this approach, the best-performing device with ODA-FeS2 NPs-based bi-functional layer shows a power conversion efficiency of 12.6% and maintains stable photovoltaic performance in 50% relative humidity for 1000 h. As a result, this study has the potential to break through the barriers for the commercialization of PSCs.

For realizing flexible perovskite solar cells (PSCs), it is important to develop low-temperature processable interlayer materials with excellent charge transporting properties. Herein, a novel polymeric hole-transport material based on 1,4-bis(4-sulfonatobutoxy)benzene and thiophene moieties (PhNa-1T) and its application as a hole-transport layer (HTL) material of high-performance inverted-type flexible PSCs are introduced. Compared with the conventionally used poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), the incorporation of PhNa-1T into HTL of the PSC device is demonstrated to be more effective for improving charge extraction from the perovskite absorber to the HTL and suppressing charge recombination in the bulk perovskite and HTL/perovskite interface. As a result, the flexible PSC using PhNa-1T achieves high photovoltaic performances with an impressive power conversion efficiency of 14.7%. This is, to the best of our knowledge, among the highest performances reported to date for inverted-type flexible PSCs. Moreover, the PhNa-1T-based flexible PSC shows much improved stability under an ambient condition than PEDOT:PSS-based PSC. It is believed that PhNa-1T is a promising candidate as an HTL material for high-performance flexible PSCs.

We report the synthesis of a new low band gap planar polymer of poly(2,5-bis(2-decyltetradecyl)-3-(5-(dithieno[3,2-b:2′,3′-d]thiophen-2-yl)thieno[3,2-b]thiophen-2-yl)-6-(thieno[3,2-b]thiophen-2-yl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione) (PTTDPP-DT-DTT) for use in organic thin film transistors (OTFTs). The polymer backbone is highly planar and well-conjugated, facilitating interchain stacking. The PTTDPP-DT-DTT-based OTFTs were fabricated and carrier mobilities were improved by using a binary solvent system: chloroform (CF):toluene (Tol), CF:chlorobenzene (CB), and CF:o-dichlorobenzene (DCB). The addition of higher boiling point solvents promoted film crystallinity with more edge-on orientations. Thus, the use of CF:DCB yielded the highest carrier mobility obtained among the devices tested. Thermal annealing further enhanced the mobility of the CF:DCB device. Atomic force microscopy images disclosed the most fibrous feature in the thermally annealed polymer film cast from CF:DCB solution. This work highlights that both the proper selection of a binary solvent and thermal annealing can manage film morphology of rigid planar conjugated polymer semiconductors effectively for high-performance OTFTs.

We report high-performance organic thin-film transistors (OTFTs) with an ultrathin active layer of difluorobenzothiadiazole-dithienosilole copolymer (PDFDT) form by using the wire bar-coating process. The top-gate/bottom contact (TG/BC) OTFTs based on bar-coated PDFDT polymer as channel material and poly(methyl methacrylate) (PMMA) as gate dielectric show a hole mobility of up to 2.2 cm2 V−1s−1 with a current ON/OFF ratio (Ion/Ioff) of 104∼105, with the mobility being two times larger than that of the spin-coated PDFDT based OTFTs. The higher mobility of the bar-coated PDFDT polymer films can be attributed to the well-organized fibril structures of the polymer chains. Importantly, two different molecular weight polymers (Mn = 23 and 34 kDa) were employed to conduct these experiments and both batches showed about the same performance, which mitigates the typical batch-to-batch variation in OTFT performance. Furthermore, we explored the operational stability of the bar-coated OTFTs in ambient air and nitrogen environments. The bias-stress and cycling tests between the ON/OFF states of the bar-coated devices showed high stability in both nitrogen and air. Conclusively, here we demonstrate that (i) a simple bar-coating process is a better method to control and obtain good polymer morphology in comparison to spin-coating, and (ii) the PDFDT polymer has great potential to provide good reproducibility and stability in large-area OTFT devices.

To transfer spin-coating based high performance polymer solar cells (PSCs) to large area using roll-to-roll compatible solution process, it is important to understand effect of the processing method and materials on morphology of bulk-heterojunction (BHJ) films. We developed PBDB-T based PSCs modules using PC71BM or nonfullerene acceptor ITIC with blade coating. It is found that crystallization of ITIC and its following aggregation are significantly affected by solvent drying dynamics which is induced by thermal heating whereas PC71BM shows similar BHJ morphology regardless heating temperature. We studied mechanism and effects of acceptors on BHJ film forming during the coating. ITIC-solvent interaction makes ITIC to form high crystalline structures and but, large aggregated domains during slow solvent evaporation at room temperature. Such aggregated morphology of PBDB-T:ITIC is much improved to optimal morphology for effective charge generation and transporting with a 50 °C heating process. As a result, PBDB-T:ITIC photovoltaic module (active area 58.5 cm2) prepared at 50 °C showed much enhanced efficiency of 9.03% than 5.0% of room temperature processed one. This result is among the highest performance of large active-area PSC modules and provides research guidelines for efficient transfer of spin-coating based small cell technology to roll-to-roll based large-area PSC modules.

Background Ligation of the intersphincteric fistula tract (LIFT) is a sphincter-preserving operation for anal fistulas. Although it has advantages in preserving continence after surgery, it is difficult to perform owing to the narrow field of view. We performed a modified surgical procedure based on the LIFT to overcome these drawbacks. Materials and methods Twenty-eight patients who were scheduled to undergo high ligation of the anal fistula tract by the lateral approach for the treatment of transsphincteric anal fistulas were prospectively studied. Instead of making a new stab incision on the intersphincteric groove, we dissected along the fistula tract from the external opening until the intersphincteric space appeared. The fistula tract was then ligated close to the internal anal sphincter with absorbable sutures, and the distal part of the ligation was cut off. A cored-out wound was left open for drainage. Results The median follow-up was 16 months (range, 8–27 months). Of the 28 patients, 19 (68%) had simple transsphincteric fistulas and 9 (32%) had complex transsphincteric fistulas. Successful fistula closure was achieved in 21 patients (75%), with a median healing time of 4 weeks (range, 3–7 weeks). None of the patients complained of any incontinence symptoms after the procedure. Of the seven patients (25%) who failed to heal successfully, two (7%) did not heal up to 2 months after surgery and five (18%) experienced recurrence after complete healing. Conclusion High ligation of the anal fistula tract by lateral approach may be a useful sphincter-sparing procedure for transsphincteric anal fistulas.

We developed p-DTS(FBTTh2)2:PC71BM-based small molecule bulk heterojunction solar cells using 1,8-diiodooctane (DIO) and small amounts of PCDTBT polymer. In the film, PCDTBT effectively suppresses the over aggregation of the p-DTS(FBTTh2)2 donor phase and promotes formation of percolating networks between the donor and acceptor phases. Moreover, the portion of p-DTS(FBTTh2)2 crystallites with the face-on orientation in the blend film is significantly increased and phase separation is decreased, which enables efficient charge generation and transport. Consequently, these solar cells consistently exhibit high fill factors and photocurrent densities and high efficiencies in the range 6.68–8.13% regardless of the DIO content (0.4–3 v/v%). In contrast, a large variation was found in the performance of the solar cells with blend films processed with DIO alone, with efficiencies of 2.75–6.68% depending on the DIO content. More importantly, the PCDTBT-processed solar cells exhibit remarkably improved stability under heating and 65 °C/85% RH. Thus, processing photoactive layers utilizing a combination of DIO and PCDTBT is an effective way of preparing promising small molecule solar cells: DIO promotes the crystallinity of the donor phase, and the intermolecular interactions between the polymer and the push–pull moiety in p-DTS(FBTTh2)2 induce distribution of donor crystallites to form percolating networks by suppressing donor over-segregation.

A series of hole-transporting materials (HTMs) based on [2,2]paracyclophane and triphenyl-amine (TPA) was synthesized. We studied the effect of the chemical structure of the HTM on the photovoltaic performance of perovskite solar cells by varying the number of TPA charge transporting components in the HTM. Tetra-TPA, in which four TPAs are incorporated into the [2,2]paracyclophane core, exhibited better hole transport properties than di-TPA and tri-TPA, which contain two and three TPAs, respectively. In particular, incorporation of the TPA group with a multi-armed structure effectively enhanced the conductivity of the HTM layer in the out-of-plane direction in the solar cell device. Due to the improved charge transport and appropriate molecular energy levels of tetra-TPA, the perovskite solar cell based on the tetra-TPA HTM achieved higher Jsc and FF values than the devices based on di-TPA and tri-TPA HTMs, with a high solar cell efficiency (17.9%).

We prepared a series of small molecules based on 7,7'-(4,4-bis(2-ethylhexyl)-4H-silolo[3,2-b:4,5-b']dithiophene-2,6-diyl)bis(4-(5'-hexyl-[2,2'-bithiophene]-5-yl)benzo[c][1,2,5]thiadiazole) with different fluorine substitution patterns (0F-4F). Depending on symmetricity and numbers of fluorine atoms incorporated in the benzo[c][1,2,5]thiadiazole unit, they show very different optical and morphological properties in a film. 2F and 4F, which featured symmetric and even-numbered fluorine substitution patterns, display improved molecular packing structures and higher crystalline properties in a film compared with 1F and 3F and thus, 2F achieved the highest OTFT mobility, which is followed by 4F. In the bulk heterojunction solar cell fabricated with PC71BM, 2F achieves the highest photovoltaic performance with an 8.14% efficiency and 0F shows the lowest efficiency of 1.28%. Moreover, the planar-type perovskite solar cell (PSC) prepared with 2F as a dopant-free hole transport material shows a high power conversion efficiency of 14.5% due to its high charge transporting properties, which were significantly improved compared with the corresponding PSC device obtained from 0F (8.5%). From the studies, it is demonstrated that low variation in the local dipole moment and the narrow distribution of 2F conformers make intermolecular interactions favorable, which may effectively drive crystal formations in the solid state and thus, higher charge transport properties compared with 1F and 3F.

We have synthesized a series of benzo[1,2-b:4,5-b′]-dithiophene (BDT)-co-thieno[3,4-b]thiophene (TT) based polymers with various alkyl side chains and bridging-atom on their TT units and studied the effects of the variation in the effective van der Waals volumes (eVol) of the side chains on the photovoltaic properties of the associated bulk heterojunction (BHJ) solar cells. eVol was found to be correlated with the degree of phase separation in the BHJ film, which affects the area of the polymer-PC71BM interface and the charge mobility. The polymer has a 2-ethylhexyl group that results in a relatively optimal BHJ film morphology, with sufficient polymer-PC71BM interfacial area for efficient charge generation and minimal charge mobility loss upon BHJ film formation. As a result, the solar cell device (2-ethylhexyl polymer) exhibits the highest power conversion efficiency of 8.25% because its short-circuit current density value (16.24 mA/cm2) and fill factor (0.674) are the highest of the synthesized polymers.