Conjugated polymer/nanocrystal nanocomposites for renewable energy applications in photovoltaics and photocatalysis.

Conjugated polymer/nanocrystal composites have attracted much attention for use in renewable energy applications because of their versatile and synergistic optical and electronic properties. Upon absorbing photons, charge separation occurs in the nanocrystals, generating electrons and holes for photocurrent flow or reduction/oxidation (redox) reactions under proper conditions. Incorporating these nanocrystals into conjugated polymers can complement the visible light absorption range of the polymers for photovoltaics applications or allow the polymers to sensitize or immobilize the nanocrystals for photocatalysis. Here, the current developments of conjugated polymer/nanocrystal nanocomposites for bulk heterojunction-type photovoltaics incorporating Cd- and Pb-based nanocrystals or quantum dots are reviewed. The effects of manipulating the organic ligands and the concentration of the nanocrystal precursor, critical factors that affect the shape and aggregation of the nanocrystals, are also discussed. In the conclusion, the mechanisms through which conjugated polymers can sensitize semiconductor nanocrystals (TiO2 , ZnO) to ensure efficient charge separation, as well as how they can support immobilized nanocrystals for use in photocatalysis, are addressed.

Achieving High Efficiency and Stability in Organic Photovoltaics with a Nanometer-Scale Twin p-i-n Structured Active Layer.

In pursuing high stability and power conversion efficiency for organic photovoltaics (OPVs), a sequential deposition (SD) approach to fabricate active layers with p-i-n structures (where p, i, and n represent the electron donor, mixed donor:acceptor, and electron acceptor regions, respectively, distinctively different from the bulk heterojunction (BHJ) structure) has emerged. Here, we present a novel approach that by incorporating two polymer donors, PBDBT-DTBT and PTQ-2F, and one small-molecule acceptor, BTP-3-EH-4Cl, into the active layer with sequential deposition, we formed a device with nanometer-scale twin p-i-n structured active layer. The twin p-i-n PBDBT-DTBT:PTQ-2F/BTP-3-EH-4Cl device involved first depositing a PBDBT-DTBT:PTQ-2F blend under layer and then a BTP-3-EH-4Cl top layer and exhibited an improved power conversion efficiency (PCE) value of 18.6%, as compared to the 16.4% for the control BHJ PBDBT-DTBT:PTQ-2F:BTP-3-EH-4Cl device or 16.6% for the single p-i-n PBDBT-DTBT/BTP-3-EH-4Cl device. The PCE enhancement resulted mainly from the twin p-i-n active layer's multiple nanoscale charge carrier pathways that contributed to an improved fill factor and faster photocurrent generation based on transient absorption studies. The PBDBT-DTBT:PTQ-2F/BTP-3-EH-4Cl film possessed a vertical twin p-i-n morphology that was revealed through secondary ion mass spectrometry and synchrotron grazing-incidence small-angle X-ray scattering analyses. The thermal stability (T80) at 85 °C of the twin p-i-n PBDBT-DTBT:PTQ-2F/BTP-3-EH-4Cl device surpassed that of the single p-i-n PBDBT-DTBT/BTP-3-EH-4Cl devices (906 vs 196 h). This approach of providing a twin p-i-n structure in the active layer can lead to substantial enhancements in both the PCE and stability of organic photovoltaics, laying a solid foundation for future commercialization of the organic photovoltaics technology.

Highly Efficient Ternary Near-Infrared Organic Photodetectors for Biometric Monitoring.

Near-infrared (NIR) small-molecule acceptors that absorb at wavelengths of up to 1000 nm are attractive for applications in organic photodetectors (OPDs) and biometrics. In this study, we incorporated IEICO-4F as the third component for PffBT4T-2OD:PC71BM-based OPDs to provide an efficient NIR response while greatly suppressing the leakage current at reverse bias. By varying the blend ratio and thickness (250-600 nm), we obtained an NIR OPD displaying an ultralow dark-current density (JD = 2.62 nA cm-2), ultrahigh detectivity [D* = 7.2 × 1012 Jones (850 nm)], high sensitivity, and photoresponsivity covering the region from the ultraviolet to the NIR. We used tapping-mode atomic force microscopy, optical microscopy, grazing-incidence wide-angle X-ray scattering, and contact angle measurements to investigate the effect of IEICO-4F on the performance of the ternary OPDs. The low compatibility of PffBT4T-2OD and IEICO-4F, originating from weak intermolecular interactions, allowed us to manipulate the degree of phase separation between the donor and acceptor in the ternary blends, leading to an optimized blend morphology featuring efficient charge separation, transport, and collection. To demonstrate its applicability, we integrated our OPD with two light-emitting diodes and used the system for precisely calculated transmissive pulse oximetry.

Enhanced performance of P3HT/TiO2 bilayer heterojunction photovoltaic device having gold nanoparticles in the donor layer.

The photovoltaic effects of blending gold nanoparticles (AuNPs) into the donor layer of a poly(3-hexylthiophene) (P3HT)/TiO2 bilayer heterojunction device have been studied. P3HT was synthesized via the modified Gragnard metathesis method and AuNPs with sizes ranging from 12 to 15 nm were formed via a reduction of HAuCl4. The blending of AuNPs into P3HT caused a lower photoluminescence (PL) intensities and a decreased energy level of the highest occupied molecular orbital (HOMO) than the pristine P3HT owing to the good electron-accepting nature of AuNPs. Upon the use of P3HT-AuNPs as the donor layer, the decreased HOMO(donor) resulted in an increased open circuit voltage (V(OC)) and thus enabled the fabricated (P3HT-AuNPs)/TiO2 bilayer heterojunction photovoltaic device to have an improved power conversion efficiency of solar energy. V(OC) as well as the overall power conversion efficiency increased with an increase in the AuNP content as a result of additional interfaces which facilitated the charge separation of excitons and percolation pathways which enhanced the electron transfer to the TiO2 acceptor. Furthermore, unannealed P3HT-AuNPs exhibited nanoholes and provided photovoltaic devices a power conversion efficiency nearly two time higher than annealed P3HT-AuNPs.

Improved Blend Film Morphology and Free Carrier Generation Provide a High-Performance Ternary Polymer Solar Cell.

Non-fullerene organic photovoltaics (OPVs) have displayed the highest power conversion efficiencies (PCEs) among OPVs. Herein, we describe a two-donor (PM6, TPD-3F)/one-acceptor (Y6) ternary blend having an optimized blend morphology that leads to improved OPV performance. Because TPD-3F has a HOMO energy level deeper than that of PM6, the value of VOC of the corresponding ternary device increased. Good miscibility between PM6 and TPD-3F, in conjunction with device optimization through the use of 1-chloronaphthalene as an additive, provided an optimized ternary blend morphology for efficient exciton dissociation and carrier transport and, therefore, larger PCE. Compared with the preoptimized PM6:Y6 binary device, the ternary device functioned with improvements in its short-circuit current density, value of VOC, and fill factor. As a result, the device PCE improved from 15.5 ± 0.19 to 16.6 ± 0.25% under AM 1.5G (100 mW cm-2) irradiation. The champion cell exhibited a PCE of 17.0%-a value that is one of the highest for a ternary OPV. Furthermore, such devices exhibited outstanding shelf lifetimes, with long-term stability in air (25 °C, 40% humidity) without encapsulation; the performance remained high (at 15.4%) after storage for 820 h.

Characterization and Optimization of Silver-Modified In0.2Cd0.8S-Based Photocatalysts.

In this research, we performed scanning electrochemical microscopy to screen M x (In0.2Cd0.8)1-x S (M = V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Ru, Ag, W, Ir, Pt, and Te) photocatalyst arrays for efficient photoelectrochemical reaction. Doping 30% Ag to form the Ag0.3(In0.2Cd0.8)0.7S electrode could result in the highest photocurrent, and also, the anode photocurrents were found to be 1 and 0.53 mA/cm2 under UV-visible and visible light, respectively, comparatively higher than that of the In0.2Cd0.8S electrode (0.45 and 0.25 mA/cm2). The highest incident photo-to-current conversion efficiency of the Ag0.3(In0.2Cd0.8)0.7S photocatalyst and In0.2Cd0.8S were found to be 64% (λ = 450 nm) and 57% (λ = 400 nm), respectively. The Mott-Schottky plots showed that In0.2Cd0.8S and Ag0.3(In0.2Cd0.8)0.7S photoelectrodes could exhibit a flat-band potential of -0.85 and -0.55 V versus Ag/AgCl, respectively. Based on these findings, the superior photocatalytic activity of the Ag0.3(In0.2Cd0.8)0.7S photoelectrode was mainly attributed to its high crystalline structure for efficient charge separation and reduction of charge recombination in the heterojunction of Ag0.3(In0.2Cd0.8)0.7S and Ag2S.

Si-Bridged Ladder-Type Small-Molecule Acceptors for High-Performance Organic Photovoltaics.

In this study, we synthesized 5,11-dihexyl-4,4,10,10-tetraoctylbenzo[1,2- b:4,5- b']bisthieno[4″,5″- b″:4‴,5‴- b‴]silolo[2″,3″- d:2‴,3‴- d']thiophene (ArSi) as a ladder-type electron-rich core for the preparation of three acceptor-donor-acceptor-type nonfullerene acceptors (NFAs)-ArSiID, ArSiID-F, and ArSiID-Cl-featuring (3-oxo-2,3-dihydro-1 H-inden-1-ylidene)malononitrile (ID), 2-(5,6-difluoro-3-oxo-2,3-dihydro-1 H-inden-1-ylidene)malononitrile (ID-F), and 2-(5,6-dichloro-3-oxo-2,3-dihydro-1 H-inden-1-ylidene)malononitrile (ID-Cl) as peripheral electron-poor units, respectively. These molecules exhibit strong absorption covering the region of 600-850 nm. The incorporation of the halogen atoms onto the terminal units adjusted the energy levels and light-harvesting ability of these materials. We employed the conjugated polymers J51 and PBDB-T, having middle optical energy gaps as donor together with these ArSi derivatives as acceptor to study the blend film morphology and the corresponding organic photovoltaic (OPV) performances. After optimization with device engineering works, a PBDB-T:ArSiID-F-based device with a power conversion efficiency up to 9.4% was achieved. This study is the first case to examine the effects of various halogen modifications on the performance of ArSi derivatives that serve as NFAs for OPVs. Our findings should encourage further investigations on this rarely studied core structure for optoelectronic applications.

Dual nanocomposite carrier transport layers enhance the efficiency of planar perovskite photovoltaics.

In photovoltaic devices, more effective transfer of dissociated electrons and holes from the active layer to the respective electrodes will result in higher fill factors and short-circuit current densities and, thus, enhanced power conversion efficiencies (PCEs). Planar perovskite photovoltaics feature an active layer that can provide a large exciton diffusion length, reaching several micrometers, but require efficient carrier transport layers for charge extraction. In this study, we employed two nanocomposite carrier transfer layers-an electron transport layer (ETL) comprising [6,6]phenyl-C61-butyric acid methyl ester (PC61BM) doped with the small molecule 4,7-diphenyl-1,10-phenanthroline (Bphen), to enhance the electron mobility, and a hole transfer layer (HTL) comprising poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) doped with molybdenum disulfide (MoS2) nanosheets, to enhance the hole mobility. We used ultraviolet photoelectron spectroscopy to determine the energy levels of these composite ETLs and HTLs; atomic force microscopy and scanning electron microscopy to probe their surface structures; and transmission electron microscopy and synchrotron grazing-incidence small-angle X-ray scattering to decipher the structures of the ETLs. Adding a small amount (less than 1%) of Bphen allowed us to tune the energy levels of the ETL and decrease the size of the PC61BM clusters and, therefore, generate more PC61BM aggregation domains to provide more pathways for electron transport, leading to enhanced PCEs of the resulting perovskite devices. We used quantitative pump-probe data to resolve the carrier dynamics from the perovskite to the ETL and HTL, and observed a smaller possibility of carrier recombination and a shorter injection lifetime in the perovskite solar cell doubly modified with carrier transport layers, resulting in an enhancement of the PCE. The PCE reached 16% for a planar inverted perovskite device featuring an ETL incorporating 0.5 wt% Bphen within PC61BM and 0.1 wt% MoS2 within PEDOT:PSS; this PCE is more than 50% higher than the value of 10.2% for the corresponding control device.

[Distribution of nitrogen and hydrogen in diamond and its significance to nucleation and growth of diamond].

From the center to the rim of natural diamond there are differences in nitrogen and C-H bond contents, suggesting that diamond was formed under varying substance conditions. Both the nitrogen and C-H bond contents tend to decrease from the center to the rim as a whole, indicaing that nitrogen and hydrogen are expended little by little during the formation of diamond. But in the middle area of the sample both the nitrogen and C-H bond contents have a tendency to increase. This implies that nitrogen and hydrogen are added into the environment of diamond formation, meanwhile nitrogen is added earlier. So the procedure of diamond formation may be divided into three stages, namely nucleation and growth in the early stage, growth in the middle stage and in the late stage. In the early and late stages nitrogen and hydrogen are consumed in the environment of diamond formation. In the middle stage nitrogen and hydrogen must be replenished for the growth of diamond, and nitrogen should be replenished earlier than hydrogen. Hydrogen is useful to the nucleation and growth of diamond. During the formation of diamond the compounds of nitrogen and hydrogen do not exist. So we must avoid the formation of compounds of nitrogen and hydrogen for the nucleation and growth of diamond if we plan to introduce hydrogen to the synthesis of diamond at high temperature and high pressure (HPHT). Implanted hydrogen in graphite for the HPHT synthesis of diamond is a good choice.

Fluorene Conjugated Polymer/Nickel Oxide Nanocomposite Hole Transport Layer Enhances the Efficiency of Organic Photovoltaic Devices.

A nanocomposite layer comprising the conjugated polymer poly[(9,9-bis(3'-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctyl)fluorene] (PFN) and nickel oxide (NiOx) has been employed as the hole transport layer (HTL) in organic photovoltaics (OPVs) featuring PBDTTBO-C8 and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as the active layer. The optimal device incorporating the PFN:NiOx nanocomposite as the HTLs displayed a power conversion efficiency (PCE) to 6.2%, up from 4.5% for the corresponding device incorporating pristine NiOx as the HTL layer: a nearly 40% improvement in PCE. X-ray photoelectron spectroscopy (XPS) was used to determine the types of chemical bonding, ultraviolet photoelectron spectroscopy (UPS) to measure the change in work function, and atomic force microscopy (AFM) to examine the morphology of the composite layers. The growth of nickel trioxide, Ni2O3, in the PFN:NiOx layer played a key role in producing the p-doping effect and in tuning the work function, thereby improving the overall device performance.

Block Copolymer-Tuned Fullerene Electron Transport Layer Enhances the Efficiency of Perovskite Photovoltaics.

In this study, we enhanced the power conversion efficiency (PCE) of perovskite solar cells by employing an electron transfer layer (ETL) comprising [6,6]phenyl-C61-butyric acid methyl ester (PC61BM) and, to optimize its morphology, a small amount of the block copolymer polystyrene-b-poly(ethylene oxide) (PS-b-PEO), positioned on the perovskite active layer. When incorporating 0.375 wt % PS-b-PEO into PC61BM, the PCE of the perovskite photovoltaic device increased from 9.4% to 13.4%, a relative increase of 43%, because of a large enhancement in the fill factor of the device. To decipher the intricate morphology of the ETL, we used synchrotron grazing-incidence small-angle X-ray scattering for determining the PC61BM cluster size, atomic force microscopy and scanning electron microscopy for probing the surface, and transmission electron microscopy for observing the aggregation of PC61BM in the ETL. We found that the interaction between PS-b-PEO and PC61BM resulted in smaller PC61BM clusters that further aggregated into dendritic structures in some domains, a result of the similar polarities of the PS block and PC61BM; this behavior could be used to tune the morphology of the ETL. The optimal PS-b-PEO-mediated PC61BM cluster size in the ETL was 17 nm, a large reduction from 59 nm for the pristine PC61BM layer. This approach of incorporating a small amount of nanostructured block copolymer into a fullerene allowed us to effectively tune the morphology of the ETL on the perovskite active layer and resulted in enhanced fill factors of the devices and thus their device efficiency.

Solution-processed zinc oxide/polyethylenimine nanocomposites as tunable electron transport layers for highly efficient bulk heterojunction polymer solar cells.

In this study, we employed polyethylenimine-doped sol-gel-processed zinc oxide composites (ZnO:PEI) as efficient electron transport layers (ETL) for facilitating electron extraction in inverted polymer solar cells. Using ultraviolet photoelectron spectroscopy, synchrotron grazing-incidence small-angle X-ray scattering and transmission electron microscopy, we observed that ZnO:PEI composite films' energy bands could be tuned considerably by varying the content of PEI up to 7 wt %-the conduction band ranged from 4.32 to 4.0 eV-and the structural order of ZnO in the ZnO:PEI thin films would be enhanced to align perpendicular to the ITO electrode, particularly at 7 wt % PEI, facilitating electron transport vertically. We then prepared two types of bulk heterojunction systems-based on poly(3-hexylthiophene) (P3HT):phenyl-C61-butryric acid methyl ester (PC61BM) and benzo[1,2-b:4,5-b́]dithiophene-thiophene-2,1,3-benzooxadiazole (PBDTTBO):phenyl-C71-butryric acid methyl ester (PC71BM)-that incorporated the ZnO:PEI composite layers. When using a composite of ZnO:PEI (93:7, w/w) as the ETL, the power conversion efficiency (PCE) of the P3HT:PC61BM (1:1, w/w) device improved to 4.6% from a value of 3.7% for the corresponding device that incorporated pristine ZnO as the ETL-a relative increase of 24%. For the PBDTTBO:PC71BM (1:2, w/w) device featuring the same amount of PEI blended in the ETL, the PCE improved to 8.7% from a value of 7.3% for the corresponding device that featured pure ZnO as its ETL-a relative increase of 20%. Accordingly, ZnO:PEI composites can be effective ETLs within organic photovoltaics.

Distribution of crystalline polymer and fullerene clusters in both horizontal and vertical directions of high-efficiency bulk heterojunction solar cells.

In this study, we used (i) synchrotron grazing-incidence small-/wide-angle X-ray scattering to elucidate the crystallinity of the polymer PBTC12TPD and the sizes of the clusters of the fullerenes PC61BM and ThC61BM and (ii) transmission electron microscopy/electron energy loss spectroscopy to decipher both horizontal and vertical distributions of fullerenes in PBTC12TPD/fullerene films processed with chloroform, chlorobenzene and dichlorobezene. We found that the crystallinity of the polymer and the sizes along with the distributions of the fullerene clusters were critically dependent on the solubility of the polymer in the processing solvent when the solubility of fullerenes is much higher than that of the polymer in the solvent. In particular, with chloroform (CF) as the processing solvent, the polymer and fullerene units in the PBTC12TPD/ThC61BM layer not only give rise to higher crystallinity and a more uniform and finer fullerene cluster dispersion but also formed nanometer scale interpenetrating network structures and presented a gradient in the distribution of the fullerene clusters and polymer, with a higher polymer density near the anode and a higher fullerene density near the cathode. As a result of combined contributions from the enhanced polymer crystallinity, finer and more uniform fullerene dispersion and gradient distributions, both the short current density and the fill factor for the device incorporating the CF-processed active layer increase substantially over that of the device incorporating a dichlorobenzene-processed active layer; the resulting power conversion efficiency of the device incorporating the CF-processed active layer was enhanced by 46% relative to that of the device incorporating a dichlorobenzene-processed active layer.