Dehua Xiong

Hydrothermal synthesis of ultrasmall CuCrO2 nanocrystal alternatives to NiO nanoparticles in efficient p-type dye-sensitized solar cells

In this study, we present a facile hydrothermal synthesis of ultrasmall delafossite CuCrO2 nanocrystals, with a typical size of 15 nm × 5 nm, and a high surface area of 87.86 m2 g−1, thermally stable up to 400 °C. The screen-printed CuCrO2 films sintered at different temperatures and under different atmospheres present different optical transmittances, tunable BET surface areas, dye adsorbing amounts, and tunable hole transport rates and hole recombination kinetics, which allows the optimization of the performance of p-type dye sensitized solar cells (DSSCs) based on CuCrO2 photocathodes. At optimized conditions, an open circuit voltage of 102 mV, a short circuit density of 0.491 mA cm−2, a fill factor of 0.398 and an overall photoconversion efficiency of 0.0194% were finally achieved for a coumarin 343 dye sensitized CuCrO2 solar cell. This record is acceptably high in comparison to a DSSC based on an NiO photocathode prepared and tested in similar experimental conditions. The light harvesting properties, charge collection capability, and flat-band potential of CuCrO2 photocathodes and the NiO photocathode have been critically compared.

Remarkable photocurrent of p-type dye-sensitized solar cell achieved by size controlled CuGaO2 nanoplates

In this paper, we report the successful hydrothermal synthesis of CuGaO2 nanoplates with a critically small size and deposition methods to fabricate effective p-type semiconductive photocathodes in dye-sensitized solar cells (DSCs). Based on an efficient P1 dye and an iodide electrolyte, the optimal CuGaO2 photocathode has achieved remarkably high photocurrent density, up to 2.05 mA cm−2. To the best of our knowledge, this is the highest achieved by nanocrystalline p-type semiconductors besides NiO. The light harvesting, charge collection in CuGaO2 and NiO based DSCs have been compared. Owing to size control of the CuGaO2 nanoplates and subsequent mechanical pressing for photocathode film deposition, the light harvesting efficiency of the CuGaO2 photocathode is greatly increased to a comparable level to that of the NiO reference. Another noteworthy feature is the remarkably high charge collection efficiency of the CuGaO2 photocathode, which should benefit from the nature of delafossite oxides with a high conductivity leading to a much higher hole diffusion coefficient in the DSC system. The open-circuit voltage is 199.3 mV, about twice as high as that of the NiO reference, benefiting from the valence band position shifting from −5.15 eV for NiO to −5.29 eV for CuGaO2versus the vacuum level.

Efficient p-type dye-sensitized solar cells based on disulfide/thiolate electrolytes

Herein, an organic redox couple 1-methy-1H-tetrazole-5-thiolate (T(-)) and its disulfide dimer (T2) redox shuttle, as an electrolyte, is introduced in a p-type dye-sensitized solar cell (DSC) on the basis of an organic dye (P1) sensitizer and nanocrystal CuCrO2 electrode. Using this iodide-free transparent redox electrolyte in conjunction with the sensitized heterojunction, we achieve a high open-circuit voltage of over 300 mV. An optimal efficiency of 0.23% is obtained using a CoS counter electrode and an optimized electrolyte composition under AM 1.5 G 100 mW cm(-2) light illumination which, to the best of our knowledge, represents the highest efficiency that has so far been reported for p-type DSCs using organic redox couples.

Enhanced Performance of p‐Type Dye‐Sensitized Solar Cells Based on Ultrasmall Mg‐Doped CuCrO2 Nanocrystals

Herein, we present ultrasmall delafossite-type Mg-doped CuCrO2 nanocrystals prepared by using hydrothermal synthesis and their first application as photocathodes in efficient p-type dye-sensitized solar cells. The short-circuit current density (Jsc ) is notably increased by approximately 27% owing to the decreased crystallite size and the enhanced optical transmittance associated with Mg doping of the CuCrO2 nanocrystalline sample. An open-circuit voltage (Voc ) of 201 mV, Jsc of 1.51 mA cm(-2) , fill factor of 0.449, and overall photoconversion efficiency of 0.132% have been achieved with the CuCr0.9 Mg 0.1 O2 dye photocathode sensitized with the P1 dye under optimized conditions. This efficiency is nearly three times higher than that of the NiO-based reference device, which is attributed to the largely improved Voc and Jsc . The augmentation of Voc and Jsc can be attributed to the lower valance band position and the faster hole diffusion coefficient of CuCr0.9 Mg 0.1 O2 compared to those of the NiO reference, respectively, which leads to a higher hole collection efficiency.

SrCl2 Derived Perovskite Facilitating a High Efficiency of 16% in Hole‐Conductor‐Free Fully Printable Mesoscopic Perovskite Solar Cells

Despite the breakthrough of over 22% power conversion efficiency demonstrated in organic-inorganic hybrid perovskite solar cells (PVSCs), critical concerns pertaining to the instability and toxicity still remain that may potentially hinder their commercialization. In this study, a new chemical approach using environmentally friendly strontium chloride (SrCl2 ) as a precursor for perovskite preparation is demonstrated to result in enhanced device performance and stability of the derived hole-conductor-free printable mesoscopic PVSCs. The CH3 NH3 PbI3 perovskite is chemically modified by introducing SrCl2 in the precursor solution. The results from structural, elemental, and morphological analyses show that the incorporation of SrCl2 affords the formation of CH3 NH3 PbI3 (SrCl2 )x perovskites endowed with lower defect concentration and better pore filling in the derived mesoscopic PVSCs. The optimized compositional CH3 NH3 PbI3 (SrCl2 )0.1 perovskite can substantially enhance the photovoltaic performance of the derived hole-conductor-free device to 15.9%, outperforming the value (13.0%) of the pristine CH3 NH3 PbI3 device. More importantly, the stability of the device in ambient air under illumination is also improved.

Synthesis and Characterization of CuAlO2 and AgAlO2 Delafossite Oxides through Low-Temperature Hydrothermal Methods

In this work, we present one-step low temperature hydrothermal synthesis of submicrometer particulate CuAlO2 and AgAlO2 delafossite oxides, which are two important p-type transparent conducting oxides. The synthesis parameters that affect the crystal formation processes and the product morphologies, including the selection of starting materials and their molar ratios, the pH value of precursors, the hydrothermal temperature, pressure, and reaction time, have been studied. CuAlO2 crystals have been synthesized from the starting materials of CuCl and NaAlO2 at 320-400 °C, and from Cu2O and Al2O3 at 340-400 °C, respectively. AgAlO2 crystals have been successfully synthesized at the low temperature of 190 °C, using AgNO3 and Al(NO3)3 as the starting materials and NaOH as the mineralizer. The detailed elemental compositions, thermal stability, optical properties, and synthesis mechanisms of CuAlO2 and AgAlO2 also have been studied. Noteworthy is the fact that both CuAlO2 and AgAlO2 can be stabilized up to 800 °C, and their optical transparency can reach 60%-85% in the visible range. Besides, it is believed the crystal formation mechanisms uncovered in the synthesis of CuAlO2 and AgAlO2 will prove insightful guildlines for the preparation of other delafossite oxides.

Modulated Charge Injection in p-Type Dye-Sensitized Solar Cells Using Fluorene-Based Light Absorbers

In this study, new pull-push arylamine-fluorene based organic dyes zzx-op1, zzx-op2, and zzx-op3 have been designed and synthesized for p-type dye-sensitized solar cells (p-DSCs). In zzx-op1, a di(p-carboxyphenyl)amine (DCPA) was used as an electron donor, a perylenemonoimide (PMID) as an electron acceptor, and a fluorene (FLU) unit with two aliphatic hexyl chains as a π-conjugated linker. In zzx-op2 and zzx-op3, a 3,4-ethylenedioxythiophene (EDOT) and a thiophene were inserted consecutively between PMID and FLU to tune the energy levels of the frontier molecular orbitals of the dyes. The structural modification broadened the spectral coverage from an onset of 700 nm for zzx-op1 to 750 nm for zzx-op3. The electron-rich EDOT and thiophene lifted up the HOMO (highest occupied molecular orbital) levels of zzx-op2 and zzx-op3, making their potential more negative than zzx-op1. When three dyes were employed in p-type DSCs with I(-)/I3(-) as a redox couple and NiO nanoparticles as hole materials, zzx-op1 exhibited impressive energy conversion efficiency of 0.184% with the open-circuit voltage (VOC) of 112 mV and the short-circuit current density (JSC) of 4.36 mA cm(-2) under AM 1.5G condition. Density functional theory calculations, transient photovoltage decay measurements, and electrochemical impedance spectroscopic studies revealed that zzx-op1 sensitized solar cell exhibited much higher charge injection efficiency (90.3%) than zzx-op2 (53.9%) and zzx-op3 (39.0%), indicating a trade-off between spectral broadening and electron injection driving force in p-type DSCs.

Near Field Enhanced Photocurrent Generation in P-type Dye-Sensitized Solar Cells

Over the past few decades, the field of p-type dye-sensitized solar cell (p-DSSC) devices has undergone tremendous advances, in which Cu-based delafossite nanocrystal is of prime interest. This paper presents an augment of about 87% improvement in photocurrent observed in a particular configuration of organic dye P1 sensitized CuCrO2 delafossite nanocrystal electrode coupled with organic redox shuttle, 1-methy-1H- tetrazole-5-thiolate and its disulfide dimer when Au nanoparticles (NPs, with diameter of about 20 nm) is added into the photocathode, achieving a power convert efficiency of 0.31% (measured under standard AM 1.5 G test conditions). Detailed investigation shows that the local electrical-magnetic field effect, induced by Au NPs among the mesoporous CuCrO2 film, can improve the charge injection efficiency at dye/semiconductor interface, which is responsible for the bulk of the gain in photocurrent.

Selective laser sintering of TiO2 nanoparticle film on plastic conductive substrate for highly efficient flexible dye-sensitized solar cell application

In this paper, we report a novel selective laser sintering of TiO2 nanoparticle (Degussa P25) film on plastic conductive substrates for highly efficient flexible dye-sensitized solar cell (DSC) applications. The so-called “selective sintering” means that the absorbed laser energy can effectively promote the electrical contacts between the TiO2 nanoparticles, but does not cause damage to the plastic conductive substrate. The choice of the near-infrared (wavelength = 1064 nm) laser source is critical for the effectiveness of the laser sintering. The laser sintering technology can effectively decrease electron transport resistance and increase recombination resistance of the TiO2 nanoparticle film characterized by electrochemical impedance spectroscopy and transient photovoltage/photocurrent decay measurements, resulting in much improved charge collection efficiency. Thus, compared to the reference sample, the laser sintered film has achieved an improved short-circuit current density from 9.2 to 10.4 mA cm−2, fill factor from 0.71 to 0.77, and solar conversion efficiency from 4.5% to 5.7%. The fast and effective selective laser sintering technique has great potential to be integrated into scalable roll-to-roll manufacturing of highly efficient flexible DSCs.