Hybrid Bulk Heterojunction Solar Cells Based on the Cooperative Interaction of Liquid Crystals within Quantum Dots and Diblock Copolymers

In this article, the conjugated rod–rod polythiophene diblock copolymers comprising a regioregular poly­(3-hexylthiophene) (P3HT) segment and a side-chain liquid-crystalline polythiophene segment bearing cyanobiphenyl mesogenic pendants (PTcbp), polythiophene-<i>b</i>-poly­{3-[10-(4′-cyanobiphenyloxy)­decyl]­thiophene} (P3HT-<i>b</i>-PTcbp), were rationally designed and synthesized. It was observed that the diblock copolymers could self-assemble into high crystalline and oriented nanofibrils upon 1,2-dichlorobenzene solvent vapor annealing, originating from the crystallization of two segments and the orientation of cyanobiphenyl side-chain mesogens. Hybrid bulk heterojunction (BHJ) solar cells were then fabricated using P3HT-<i>b</i>-PTcbp as electron donors and ZnO and CdS quantum dots (QDs) modified by 4′-hydroxy-[1,1′-biphenyl]-4-carbonitrile (cbp) liquid-crystalline ligands (cbp@ZnO and cbp@CdS) as electron acceptors. The interaction between the cbp ligands on the surface of ZnO and CdS QDs and cyanobiphenyl side-chain mesogens of diblock copolymers promoted the cooperative self-assembly and controllable well-dispersion of QDs in the polymer matrix and, as a consequence, yielded an intimately contacted polymer–QD nanocomposites. The power conversion efficiency (PCE) of the device based on P3HT-<i>b</i>-PTcbp/cbp@ZnO hybrids was improved by 2.6 times compared with that of P3HT/ZnO hybrids from 0.58 to 0.97. In addition, an overall PCE of a homologous device based on the P3HT-<i>b</i>-PTcbp/cbp@CdS hybrid active layer reached 2.3%. The research paved the way for the further development of high-efficiency hybrid BHJ solar cells by introducing block copolymer nanofibrils with favored crystalline domain orientations and liquid-crystalline organization properties

In Situ Fabricating One-Dimensional Donor–Acceptor Core–Shell Hybrid Nanobeams Network Driven by Self-Assembly of Diblock Copolythiophenes

In situ growth of cadmium sulfide (CdS) quantum dots (QDs) was achieved directly through solvent-assisted grafting in the self-assembled templates of amphiphilic all conjugated diblock copolythiophene, poly­(3-hexylthiophene)-<i>b</i>-poly­(3-(2-(2-(2-methoxyethoxy)­ethoxy)­ethoxy)­methylthiophene) (P3HT-<i>b</i>-P3TEGT) and gas–solid reaction. Such diblock polymer templates allowed a desired amount of cadmium sulfide salt (Cd­(Ac)₂) to easily accomplish dispersion and self-assembly via controlled assembling block copolymers in selective solvents. After P3HT-<i>b</i>-P3TEGT polymer templates grafted with Cd²⁺ precursor (P3HT-<i>b</i>-P3TEGT/Cd²⁺) reacting in hydrogen sulfide (H₂S) gas, one-dimensional core–shell nanobeams network P3HT-<i>b</i>-P3TEG/CdS (donor–acceptor) was formed with excellent phase separation between P3HT-<i>b</i>-P3TEGT crystalline domains and inorganic CdS QDs domains at nanoscales, which was driven by the interaction between oxygen atoms of ethylene oxide side chains and Cd²⁺ ions, and the thermodynamic equilibrium between polymer chains deformation. The one-dimensional wire-like nanostructure were highly desirable for the active layers in photovoltaic devices as providing high carrier mobility, large interfacial area between electron donor and acceptor, and highly efficient transport pathways to improve the power conversion efficiency (PCE) of hybrid bulk heterojunction solar cells

Sulfonate Poly(aryl ether sulfone)-Modified PEDOT:PSS as Hole Transport Layer and Transparent Electrode for High Performance Polymer Solar Cells

Polymer solar cells (PSCs) with high short current density (<i>J</i>_sc) have been fabricated through a facile way by using a low-cost polyelectrolyte-modified poly­(3,4- ethylenedioxythiophene):poly­(styrenesulfonate) (PEDOT:PSS, P VP Al 4083) bilayer film as anode buffer layer. Spin-coating a layer of sulfonate poly­(aryl ether sulfone) (SPES) on the surface of PEDOT:PSS hole-transporting layer (HTL) is found to dramatically improve the <i>J</i>_sc value even up to 21.66 mA cm^–2. The notable <i>J</i>_sc is demonstrated to be correlated with interaction between the SPES and PEDOT, which removes the insulator of PSS with formation of continuous PEDOT domains, consequently leading to the improved conductivity and more imitate interfacial contact. It should be noted that the notable <i>J</i>_sc also partly results from the effect of a second anode due to the high conductivity of SPES-modified PEDOT:PSS. Through systematically investigation on a series of devices with different areas, it can be found that a real effective area of the devices should be carefully addressed to exclude the effect of a second anode, especially when a highly conductive interfacial material is incorporated. More interestingly, apart from the successful application in HTL, SPES also works well as transparent electrode. Compared with the pristine PEDOT:PSS (PH1000) anode, SPES-modified PH1000 as transparent anode achieves a dramatically increased performance in the ITO-free PSCs together with overall improved parameters, even equal to the one based on ITO anode. These findings indicate that solution-processed SPES shows a great potential in the fabrication of highly efficient PSCs as well as large-area, flexible printable PSCs

Fluorinated Reduced Graphene Oxide as an Efficient Hole-Transport Layer for Efficient and Stable Polymer Solar Cells

In this work, we have rationally designed and successfully synthesized a reduced graphene oxide (GO) functionalized with fluorine atoms (F-rGO) as a hole-transport layer (HTL) for polymer solar cells (PSCs). The resultant F-rGO has an excellent dispersibility in dimethylformamide without any surfactants, leading to a good film-forming property of F-rGO for structuring a stable interface. The recovery of conjugated CC bonds in GO oxide after reduction increases the conductivity of F-rGO, which enhances the short-circuit current density of photovoltaic devices from 15.65 to 16.89 mA/cm². A higher work function (WF) (5.1 eV) of F-rGO than that of GO (4.9 eV) is attributed to the fluorine group with a high electronegativity. Naturally, the better-matched WF with the highest occupied molecular orbital level of the PTB7-Th (5.22 eV) donor induces an improved energy alignment in devices, resulting in a superior open-circuit voltage of the device (0.776 vs 0.786 V). Consequently, the device with F-rGO as the HTL achieves a higher power conversion efficiency (8.6%) with long-term stability than that of the devices with GO HTLs and even higher than that of the poly­(3,4-ethylenedioxythiophene)/poly­(styrenesulfonate) (PEDOT/PSS) control device. These results clearly verify that the F-rGO is a promising hole-transport material and an ideal replacement for conventional PEDOT/PSS, further promoting the realization of low-cost, solution-processed, high-performance, and high-stability PSCs

Versatile Molybdenum Isopropoxide for Efficient Mesoporous Perovskite Solar Cells: Simultaneously Optimized Morphology and Interfacial Engineering

The high-quality CH₃NH₃PbI₃ film morphology and delicate interfacial modification are critical to achieve high-performance perovskite solar cells (PSCs). Here, we report a facile and efficient method to optimize the morphology and interface of a perovskite solar cell by molybdenum isopropoxide (Mo-IPA) solution treatment during the fabrication process of the perovskite film. After simply being treated with Mo-IPA, both highly crystalline perovskite film and MoO_<i>X</i> interfacial layer could be simultaneously achieved. The Mo-IPA treatment can induce a denser and more uniform morphology of CH₃NH₃PbI₃ with larger crystals size than pure isopropyl alcohol (IPA) treatment. At the same time, the formation of MoO_<i>X</i> can effectively elevate the valence band maximum (VBM) of the perovskite, as a result to favor a better energy alignment with 2,2′,7,7′-tetrakis­(<i>N</i>,<i>N</i>-di-<i>p</i>-methoxyphenylamine)­9,9′-spirobifluorene (Spiro-MeOTAD) hole transport layer (HTL) for efficient hole extraction. With those excellent properties obtained, the photovoltaic performance of the PSCs was remarkably increased from 10.8% to 12.0%

Grain Boundary Modification via F4TCNQ To Reduce Defects of Perovskite Solar Cells with Excellent Device Performance

Solar cells based on hybrid organic–inorganic metal halide perovskites are being developed to achieve high efficiency and stability. However, inevitably, there are defects in perovskite films, leading to poor device performance. Here, we employ an additive-engineering strategy to modify the grain boundary (GB) defects and crystal lattice defects by introducing a strong electron acceptor of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) into perovskite functional layer. Importantly, it has been found that F4TCNQ is filled in GBs and there is a significant reduction of metallic lead defects and iodide vacancies in the perovskite crystal lattice. The bulk heterojunction perovskite–F4TCNQ film exhibits superior electronic quality with improved charge separation and transfer, enhanced and balanced charge mobility, as well as suppressed recombination. As a result, the F4TCNQ doped perovskite device shows excellent device performance, especially the reproducible high fill factor (up to 80%) and negligible hysteresis effect

When Al-Doped Cobalt Sulfide Nanosheets Meet Nickel Nanotube Arrays: A Highly Efficient and Stable Cathode for Asymmetric Supercapacitors

Although cobalt sulfide is a promising electrode material for supercapacitors, its wide application is limited by relative poor electrochemical performance, low electrical conductivity, and inefficient nanostructure. Here, we demonstrated that the electrochemical activity of cobalt sulfide could be significantly improved by Al doping. We designed and fabricated hierarchical core-branch Al-doped cobalt sulfide nanosheets anchored on Ni nanotube arrays combined with carbon cloth (denoted as CC/H-Ni@Al-Co-S) as an excellent self-standing cathode for asymmetric supercapacitors (ASCs). The combination of structural and compositional advantages endows the CC/H-Ni@Al-Co-S electrode with superior electrochemical performance with high specific capacitance (1830 F g^–1/2434 F g^–1 at 5 mV s^–1/1 A g^–1) and excellent rate capability (57.2%/72.3% retention at 1000 mV s^–1/100 A g^–1). The corresponding all-solid-state ASCs with CC/H-Ni@Al-Co-S and multilayer graphene/CNT film as cathode and anode, respectively, achieve a high energy density up to 65.7 W h kg^–1 as well as superb cycling stability (90.6% retention after 10 000 cycles). Moreover, the ASCs also exhibit good flexibility and stability under different bending conditions. This work provides a general, effective route to prepare high-performance electrode materials for flexible all-solid-state energy storage devices

Large-Scale Stretchable Semiembedded Copper Nanowire Transparent Conductive Films by an Electrospinning Template

With recent emergence of wearable electronic devices, flexible and stretchable transparent electrodes are the core components to realize innovative devices. The copper nanowire (CuNW) network is commonly chosen because of its high conductivity and transparency. However, the junction resistances and low aspect ratios still limit its further stretchable performance. Herein, a large-scale stretchable semiembedded CuNW transparent conductive film (TCF) was fabricated by electrolessly depositing Cu on the electrospun poly­(4-vinylpyridine) polymer template semiembedded in polydimethylsiloxane. Compared with traditional CuNWs, which are as-coated on the flexible substrate, the semiembedded CuNW TCFs showed low sheet resistance (15.6 Ω·sq^–1 at ∼82% transmittance) as well as outstanding stretchability and mechanical stability. The light-emitting diode connected the stretchable semiembedded CuNW TCFs in the electric circuit still lighted up even after stretching with 25% strain. Moreover, this semiembedded CuNW TCF was successfully applied in polymer solar cells as a stretchable conductive electrode, which yielded a power conversion efficiency of 4.6% with 0.1 cm² effective area. The large-scale stretchable CuNW TCFs show potential for the development of wearable electronic devices

High-Performance Polymer Solar Cells Realized by Regulating the Surface Properties of PEDOT:PSS Interlayer from Ionic Liquids

Significant efforts have been dedicated to the interface engineering of organic photovoltaic device, suggesting that the performance and aging of the device are not only dependent on the active layer, but also governed by the interface with electrodes. In this work, controllable interfacial dipole and conductivity have been achieved in ionic liquids (ILs) modified poly­(3,4-ethylenedioxythiophene):poly­(styrenesulfonate) (PEDOT:PSS). We conclude that an appropriate interfacial conductivity is as essential as the suitable work function for an efficient buffer layer. Through forming favorable dipoles for hole transportation and reducing the film resistance by [HOEMIm]­[HSO4] treatment, an averaged performance of 8.64% is obtained for OPVs based on PTB7:PC71BM bulk heterojunction with improved stability. However, the improvement of performance is inconspicuous for OPVs based on PTB7-Th:PC71BM bulk heterojunction due to the incompetent energy level of high concentration ILs-modified PEDOT:PSS. The enhanced in-plane conductivity will reduce shunt resistance, and produce a fake high short-circuit current density (<i>J</i>_sc) with a lower fill factor. We point out that the <i>J</i>_sc can be improved by decreasing series resistance; meanwhile, the accompanying reduced shunt resistance has an unfavorable effect on device performance

Roll-To-Roll Printing of Meter-Scale Composite Transparent Electrodes with Optimized Mechanical and Optical Properties for Photoelectronics

Flexible transparent electrodes are an indispensable component for flexible optoelectronic devices. In this work, the meter-scale composite transparent electrodes (CTEs) composed of poly­(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) and Ag grid/polyethylene terephthalate (PET) with optimized mechanical and optical properties are demonstrated by slot–die roll-to-roll technique with solution printing method under a low cost ($15–20 per square meter), via control of the viscosity and surface energy of PEDOT:PSS ink as well as the printing parameters. The CTEs show excellent flexibility remaining 98% of the pristine value after bending 2000 times under various bending situations, and the square resistance (<i>R</i>_s) of CTEs can be reduced to 4.5–5.0 Ω/sq with an appropriate transmittance. Moreover, the optical performances, such as haze, extinction coefficient, and refractive index, are investigated, as compared with indium tin oxide/PET, which are potential for the inexpensive optoelectronic flexible devices. The CTEs could be successfully employed in polymer solar cells with different areas, showing a maximal power conversion efficiency of 8.08%