•We first synthesized CuCr1-xGaxO2 with 15–50 nm through hydrothermal method.•The Ga3+ ions were substituted at Cr3+ in CuCrO2 and formed CuCr1-xGaxO2.•The optical transmittance of CuCr1-xGaxO2 films about 60–75% in the visible region.•The valence band energy position of CuCr1-xGaxO2 is range from 5.29 to 5.44 eV.•CuCr1-xGaxO2 nanocrystals were applied as photocathodes in p-type DSSC devices.Pure phase of CuCr1-xGaxO2 (x = 0.10, 0.20, 0.30, 0.40, 0.50.) nanocrystals with the crystal size ranging from 15 nm to 50 nm were synthesized through hydrothermal method. The crystal structure, morphology, element composition information, optical properties and valence band energy position of these delafossites were analyzed by XRD, SEM/EDS, TEM/EDS, XPS/UPS, and Uv–vis measurements. It was found that the Ga3+ ions were perfectly substituted at Cr3+ in CuCrO2 lattice and finally formed the CuCr1-xGaxO2 solid solution. The crystal size of CuCr1-xGaxO2 enlarged from 15 nm to 50 nm with the increasing of Ga composition x from 0.10 to 0.50. The optical transmittance of these CuCr1-xGaxO2 films approached about 60–75% in the visible region and the direct band gap values around 3.25–3.30 eV. The valence band energy position of these CuCr1-xGaxO2 nanocrystals ranged from 5.29 to 5.44 eV, which is much lower than traditional NiO nanoparticles used in p-type dye sensitized solar cells (DSSCs). Moreover, these CuCr1-xGaxO2 nanocrystals were applied as photocathodes in p-type DSSC devices, and the CuCr0.90Ga0.10O2 based solar cell show the best performance (134 mV, 1.56 mA cm−2, 0.10%) after roughly optimizing the composition and the thickness of photocathode films.We present CuCr1-xGaxO2 nanocrystals with 15–50 nm were prepared through hydrothermal method and applied as photocathodes in p-type DSCCs.Download high-res image (297KB)Download full-size image

Perovskite solar cell (PVSC), after its invention since 2009, has attracted tremendous attention from both academia and industry, because of its low cost, ease of manufacturing features and the sky-rocketing efficiencies being achieved within such a short period of time. Currently, the new efficiency record has reached 21.0%, comparable to that of the commercialized PV technologies developed for decades, such as multi-crystalline Si, CIGS and CdTe thin film solar cells. It is very possible that PVSCs would one day step over the threshold of marketization, share or even overturn the current PV market dominated by crystalline-Si solar cells. However, there are still several obstacles to be overcome on the road towards PVSC industrialization. This paper has reviewed the brief developing history and the current research status of PVSCs, and explained: Why PVSCs are so important in the next-generation solar cells, why organometal halide perovskites work so well as light absorbers, and what the inherent differences are among different cell configurations. The prospects on how to realize scale-up industrialization of PVSCs have also been given in the sequence of efficiency, stability, cost, toxicity, and short-term objectives. Resolutions to the remaining challenges according to their orders of technical difficulty and importance have also been discussed.

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.

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.Keywords: charge injection; fluorene; NiO; organic sensitizer; p-type dye-sensitized solar cells;

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.

Self-standing single crystalline NiCo2S4 hollow nanorod arrays are prepared for catalysing the polysulfide redox couple in quantum dot-sensitized solar cells (QDSCs). The QDSCs using NiCo2S4 as a counter electrode (CE) achieved a power conversion efficiency of 4.22%, which exceeds the performance of QDSCs based on a Pt CE by 38.4%.

Tandem structured dye-sensitized solar cells (DSSCs) can take full advantage of sunlight, effectively broadening the absorption spectrum of the cell, resulting in a higher open circuit voltage or short circuit current than that of the conventional DSSC with single light absorber. The theoretical maximum efficiency is therefore suggested to be over the Schottky-Queisser limit of 33%. Accordingly, tandem design of DSSC is thought to be a promising way to break the performance bottleneck of DSSC. Besides, the tandem designs also broaden the application diversity of DSSC technology, which will accelerate its scale-up industrial application. In this paper, we have reviewed the recent progress on photo-electrochemical applications associated with kinds of tandem designs of DSSCs, in general, which are divided into three kinds: “n-type DSSC + n-type DSSC,” “n-type DSSC + p-type DSSC” and “n-type DSSC + other solar conversion devices.” The working principles, advantages and challenges of these tandem structured DSSCs have been discussed. Some possible solutions for further studies have been also pointed out together.

Self-standing single crystalline NiCo2S4 hollow nanorod arrays are prepared for catalysing the polysulfide redox couple in quantum dot-sensitized solar cells (QDSCs). The QDSCs using NiCo2S4 as a counter electrode (CE) achieved a power conversion efficiency of 4.22%, which exceeds the performance of QDSCs based on a Pt CE by 38.4%.

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.