Chao Yi

Polyaniline-Modified Oriented Graphene Hydrogel Film as the Free-Standing Electrode for Flexible Solid-State Supercapacitors

In this study, we report polyaniline (PANI)-modified oriented graphene hydrogel (OGH) films as the free-standing electrode for flexible solid-state supercapacitors (SCs). The OGH films are prepared by a facile filtration method using chemically converted graphene sheets and then introduced to PANI on the surface of OGH films by in situ chemical polymerization. The PANI-modified OGH films possess high flexibility, high electrical conductivity, and mechanical robustness. The flexible solid-state SCs based on the PANI-modified OGH films exhibit a specific capacitance of 530 F/g, keeping 80% of its original value up to 10 000 charge-discharge cycles at the current density of 10 A/g. Remarkably, the flexible solid-state SCs maintain ∼100% capacitance retention bent at 180° for 250 cycles. Moreover, the flexible solid-state SCs are further demonstrated to be able to light up a red-light-emitting diode. These results indicate that the flexible solid-state SCs based on PANI-modified OGH films as the free-standing electrode have potential applications as energy-storage devices.

Solution-Processed Fe3O4 Magnetic Nanoparticle Thin Film Aligned by an External Magnetostatic Field as a Hole Extraction Layer for Polymer Solar Cells

We report, for the first time, the effect of a solution-processed Fe3O4 magnetic nanoparticle (MNP) thin film and a Fe3O4 MNP thin film aligned by an external magnetostatic field, used as a hole extraction layer (HEL), respectively, in polymer solar cells (PSCs). The thin film of a Fe3O4 MNP shows a smoother surface, better transparency, and higher electrical conductivity than that of a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) thin layer. Moreover, the thin film of a Fe3O4 MNP aligned by an external magnetostatic field possesses an enhanced electrical conductivity and lower internal series resistance, thus leading to greater than 13% enhancement in the power conversion efficiency of PSCs than those using a PEDOT:PSS thin film. It was also found that PSCs incorporated with a Fe3O4 MNP shows better stability compared with those using PEDOT:PSS as an anode buffer layer. These results demonstrated that utilization of a Fe3O4 MNP as a HEL in PSCs blazes a trail to achieve highly efficient and long-time-stable devices.

Enhanced Thermoelectric Properties of Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) by Binary Secondary Dopants.

UNLABELLED To simultaneously increase the electrical conductivity and Seebeck coefficient of poly(3,4-ethylenedioxythiophene):polystyrenesulfonate ( PEDOT PSS) was a challenge for realizing efficient organic thermoelectrics. In this study, for the first time, we report both increased electrical conductivities and Seebeck coefficients, hence, enhanced thermoelectric properties of PEDOT PSS thin films by doped with binary secondary dopants, dimethyl sulfoxide (DMSO) and poly(ethylene oxide) (PEO). Without modifying film morphology, the molar ratios of PEDOT to PSS are tuned by PEO, resulting in increased proportions of PEDOT in the bipolaron states. Our study provides a facile route to optimizing thermoelectric properties of PEDOT PSS thin films.

Effects of Magnetic Nanoparticles and External Magnetostatic Field on the Bulk Heterojunction Polymer Solar Cells

The price of energy to separate tightly bound electron-hole pair (or charge-transfer state) and extract freely movable charges from low-mobility materials represents fundamental losses for many low-cost photovoltaic devices. In bulk heterojunction (BHJ) polymer solar cells (PSCs), approximately 50% of the total efficiency lost among all energy loss pathways is due to the photogenerated charge carrier recombination within PSCs and low charge carrier mobility of disordered organic materials. To address these issues, we introduce magnetic nanoparticles (MNPs) and orientate these MNPS within BHJ composite by an external magnetostatic field. Over 50% enhanced efficiency was observed from BHJ PSCs incorporated with MNPs and an external magnetostatic field alignment when compared to the control BHJ PSCs. The optimization of BHJ thin film morphology, suppression of charge carrier recombination, and enhancement in charge carrier collection result in a greatly increased short-circuit current density and fill factor, as a result, enhanced power conversion efficiency.

Conductive Water/Alcohol-Soluble Neutral Fullerene Derivative as an Interfacial Layer for Inverted Polymer Solar Cells with High Efficiency

Dipole induced vacuum level shift has been demonstrated to be responsible for the enhanced efficiency in polymer solar cells (PSCs).The modified energy level alignment could reduce the energy barrier and facilitate charge transport, thereby increasing the efficiency of PSCs. Herein, we report a new mechanism toward enhanced efficiency by using a nondipolar water/alcohol-soluble neutral fullerene derivative to reengineer the surface of the zinc oxide (ZnO) electron extraction layer (EEL) in inverted PSCs. Because of the neutral property (ion-free) of the fullerene derivatives, no dipole moment was introduced at the EEL/active layer interface. A negligible change in open-circuit voltage was observed from inverted PSCs with the neutral fullerene derivative layer. The neutral fullerene derivative layer greatly increased the surface electronic conductivity of the ZnO EEL, suppressed surface charge recombination, and increased the short-circuit current density and fill factor. An overall power conversion efficiency increase of more than 30% from inverted PSCs was obtained. These results demonstrate that the surface electronic conductivity of the EEL plays an important role in high performance inverted PSCs.

Enhanced performance of polymer solar cells using PEDOT:PSS doped with Fe3O4 magnetic nanoparticles aligned by an external magnetostatic field as an anode buffer layer.

Low efficiency and poor stability are two major obstacles limiting the manufacturing of renewable and cost-effective polymer solar cell (PSCs). To address these problems, solution-processed poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) doped with Fe3O4 magnetic nanoparticles ((PEDOT:PSS):Fe3O4), and above (PEDOT:PSS):Fe3O4 thin film aligned by an external magnetostatic field ([(PEDOT:PSS):Fe3O4] W/H) were used as the anode buffer layer for PSCs, respectively. As compared with PSCs with PEDOT:PSS as an anode buffer layer, 38.5% enhanced efficiency and twice improved stability are observed from PSCs incorporated with [(PEDOT:PSS):Fe3O4] W/H anode buffer layer. It was found that enhanced efficiency and improved stability resulted from a combination of reduced acidity of PEDOT:PSS and enhanced electrical conductivity that originated from generated counterions and the paramagnetism of Fe3O4 magnetic nanoparticles by an external magnetostatic field.

Efficient polymer solar cells fabricated from solvent processing additive solution

In this study, we investigate the device performance of bulk heterojunction (BHJ) polymer solar cells (PSCs) fabricated from pristine chlorobenzene (CB) solution, CB solutions with different concentrations of solvent processing additive, chloronaphthalene (CN) which has a high boiling point temperature, and pristine CN solution. An efficiency of 7.12% is observed from PSCs processed from pristine CN solution as compared with 4.01% of that from pristine CB solution. The correlation between the efficiency of PSCs with the concentrations of CN was systematically studied by absorption spectra, atomic force microscopy and cross-section transmission electron microscopy images, wide angle X-ray diffraction and grazing incidence small angle X-ray patterns of BHJ active layers and impedance spectroscopies of BHJ PSCs. It was found that the addition of CN into CB solution does not affect the crystallization or the molecular packing of the donor polymer in BHJ layers, but it changes the film morphology of the BHJ layers. The phase separation between the donor polymer and fullerene derivatives was reduced and BHJ layers were redistributed as the concentration of CN is increased in CB solutions. As a result, increased ratios of the donor polymer to fullerene derivatives, and high hole mobilities of the donor polymer in BHJ layers were obtained for the resultant films. Consequently, a high efficiency was observed from PSCs processed from CN solution rather than from CB solution. Our findings provide a method to approach highly efficient PSCs.

Protonation process of conjugated polyelectrolytes on enhanced power conversion efficiency in the inverted polymer solar cells

Abstract. In this study, two conjugated polyelectrolytes, polythiophene derivative (PTP) and poly[(9,9-bis [6′-N, N, N-trimethylammonium] hexyl)-fluorenylene-phenylene] dibromide (PFP), are utilized to modify the surface properties of ZnO electron extraction layer (EEL) in the inverted polymer solar cells (PSCs). Both higher short-circuit current densities and larger open-circuit voltages were observed from the inverted PSCs with ZnO/PFP or ZnO/PTP as compared with those only with ZnO EEL. The protonation process for PTP and PFP in solution is distinguished. Overall, more than 40% enhanced power conversion efficiency (PCE) from the inverted PSCs with ZnO/PFP, in which the PFP could be fully ionized in deionized water, and more than 30% enhanced PCE from the inverted PSCs with ZnO/PTP, as the case that the PTP could not be fully ionized in deionized water, as compared with the inverted PSCs with ZnO EEL were observed, respectively. These results demonstrate that the conjugated polyelectrolytes play an important role in enhancement of device performance of inverted PSCs and that the protonation process of the conjugated polyelectrolytes is critical to the modification for EEL in PSCs.

Highly electrically conductive polyethylenedioxythiophene thin films for thermoelectric applications

In this study, we report the utilization of protonic acids to treat polyethylene glycol-triblock-polypropylene glycol (PP) modified polyethylenedioxythiophene (PEDOT) doped with tosylate (Tos−) counter-ion (PP-modified PEDOT:Tos) thin films. Investigations using absorption, Raman, electron spin resonance and X-ray photoemission spectroscopies indicate that nearly 100% enhanced electrical conductivity and over a 30% improved power factor observed from the PP-modified PEDOT:Tos thin films with protonic acid treatment are attributed to the increased densities of the polaron state and the stabilized densities of the bipolaron state. Further studies by grazing incidence wide angle X-ray scattering and atomic force microscopy reveal that the crystal structure, amorphous regions, and the size of the exchanging counter ion have great influences on the electrical conductivities, the Seebeck coefficients and the power factors. Our studies provide a facile route to realize highly electrically conductive polymers for the development of effective organic thermoelectric devices.

Efficient Perovskite Hybrid Solar Cells via Controllable Crystallization Film Morphology

Perovskite hybrid solar cells (pero-HSCs) have attracted significant attention due to their promising photovoltaic efficiency, solution processibility, and low-cost manufacturing process. In this study, we report efficient solution-processed planar heterojunction (PHJ) pero-HSCs. By fine-tuning the film formation procedures, uniform perovskite thin films with high surface coverage and superior optical and electrical properties are produced, which results in over 14% efficiency. These results demonstrate that the quality of perovskite thin films plays an important role in approaching efficient solution-processed PHJ pero-HSCs.