Li’e Mo

Mesoporous TiO2 Yolk-Shell Microspheres for Dye-sensitized Solar Cells with a High Efficiency Exceeding 11%.

Yolk-shell TiO2 microspheres were synthesized via a one-pot template-free solvothermal method building on the aldol condensation reaction of acetylacetone. This unique structure shows superior light scattering ability resulting in power conversion efficiency as high as 11%. This work provided a new synthesis system for TiO2 microspheres from solid to hollow and a novel material platform for high performance solar cells.

One-Pot Synthesis of Mesoporous TiO2 Micropheres and Its Application for High-Efficiency Dye-Sensitized Solar Cells

TiO2 microspheres are of great interest for a great deal of applications, especially in the solar cell field. Because of their unique microstructure and light-scattering effect, TiO2 microsphere-based solar cells often exhibit superior photovoltaic performance. Hence, exploring new suitable TiO2 microspheres for high-efficiency solar cells is essential. In this work, we demonstrate a facile one-pot solvothermal approach for synthesis of TiO2 microspheres using acetone as solvent. The as-prepared TiO2 microspheres are composed of densely interconnected nanocrystals and possess a high specific surface area up to 138.47 m(2) g(-1). As the photoanode, the TiO2 microsphere-based DSSC gives higher dye loading and light adsorption ability as well as longer electron lifetime, resulting in higher short-circuit current value and superior power conversion efficiency (PCE) compared with Dyesol 18 nm TiO2 nanoparticle paste. Finally, the TiO2 microsphere-based DSSC were optimized by adding a TiO2 nanocrystal underlayer and TiCl4 post-treatment, giving a high PCE of 10.32%.

Enhanced photovoltaic performance of dye-sensitized solar cells using a highly crystallized mesoporous TiO2 electrode modified by boron doping

Highly crystallized boron-doped anatase TiO2 nanoparticles are prepared by a facile synthetic route and successfully used as the photoanode of dye-sensitized solar cells (DSCs). We have observed that the boron doping could improve the crystallinity of TiO2. Moreover, the highly crystallized anatase boron-doped TiO2 were analyzed by electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS) and UV-vis spectroscopy, and the internal resistances of the boron-doped DSCs were studied by measuring the electrochemical impedance spectra (EIS). The improved photocurrent density of the boron-doped DSCs is due to a significant enhancement of IPCE in the range 370–650nm in comparison with that of the undoped DSC. Meanwhile, the energy-conversion efficiency of the cell based on the B-doped TiO2 electrode is enhanced significantly, by about 9%, compared to that of the undoped DSC. Overall, DSCs based on B-doped electrodes show good stability and remain over 95% of their initial efficiency under visible light soaking for more than 2400 h.

Characteristics of dye-sensitized solar cells based on the TiO2 nanotube/nanoparticle composite electrodes

The influence of TiO2 nanotubes on the charge collection efficiency and the dynamics of electron transport and recombination in dye-sensitized solar cells (DSCs) based on the TiO2 nanotube/nanoparticle composite films were investigated in this paper. Electrochemical impedance spectroscopy was employed to quantify the charge transfer resistance of DSCs. The different transport and recombination properties of DSCs were studied by frequency-resolved modulated photocurrent/photovoltage spectroscopies. It was shown that the electrons had a longer lifetime in the nanotubes and retarded recombination more significantly than in the nanoparticles. But with increasing the amount of nanotube, the electron pathway was extended seriously in these network structures resulting in increased recombination chances. In addition, the 5 wt% nanotube DSC had the highest charge collection efficiency among all the DSCs, which yielded a high photovoltaic conversion efficiency of 9.79% under simulated AM 1.5 sunlight (100 mW cm−2).

Fine Tuning of Nanocrystal and Pore Sizes of TiO2 Submicrospheres toward High Performance Dye-Sensitized Solar Cells

In general, the properties and performance of mesoporous TiO2 are greatly dependent on its crystal size, crystallinity, porosity, surface area, and morphology; in this regard, design and fine-tuning the crystal and pore sizes of the TiO2 submicrospheres and investigating the effect of these factors on the properties and photoelectric performance of dye-sensitized solar cells (DSSCs) is essential. In this work, uniform TiO2 submicrospheres were synthesized by a two-step procedure containing hydrolysis and solvothermal process. The crystal and pore sizes of the TiO2 submicrospheres were fine-tuned and controlled in a narrow range by adjusting the quantity of NH4OH during the solvothermal process. The effect of crystal and pore size of TiO2 submicrosphere on the performance of the DSSCs and their properties including dye-loading capacity, light scattering effect, power conversion efficiency (PCE), incident photon-to-electron conversion efficiencies (IPCEs), and electron recombination were compared and analyzed. The results show that increasing pore size plays a more significant role in improving the dye-loading capacity and PCE than increasing surface area, and an overall PCE value of 8.62% was obtained for the device with a 7.0 μm film thickness based on the TiO2 submicrospheres treated with 0.6 mL of NH4OH. Finally, the best TiO2 submicrosphere based photoanode film was optimized by TiCl4 treatment, and increasing film thickness and a remarkable PCE up to 11.11% were achieved.

Superior energy band structure and retarded charge recombination for Anatase N, B codoped nano-crystalline TiO2 anodes in dye-sensitized solar cells

This work reports the preparation of N, B codoped TiO2 (N, B–TiO2) electrodes in dye-sensitized solar cells (DSCs) by a facial modified sol–gel method. After the nitrogen and boron dopants incorporated into the TiO2 electrodes, the cubic-like TiO2 nanocrystallites with diameters of 22∼24 nm were obtained efficiently. The back electron transfer of the DSC based on the N, B–TiO2 electrode was studied by measuring the electrochemistry impedance spectra (EIS) and the EIS for the DSCs showed that the enhanced electron lifetime for the dye-sensitized B, N–TiO2 solar cells could be attributed to the formation of an O–Ti–B–N bond in the TiO2 photoelectrode, which retards electron recombination at the dyed N, B–TiO2 photoelectrode/electrolyte interface after N, B codoping as compared to the undoped DSC. We found that a high efficiency of 8.4% for the DSC (active area:4 cm2) based on the N, B–TiO2 anode under 0.2 sun illumination was received. In particular, the photovoltaic performance of the DSC under high temperature conditions (60 °C) and one-sun light soaking over a time of more than 1100 h showed that the DSC based on the N, B–TiO2 electrode exhibited a better stability compared to the undoped DSC. The excellent photoelectrochemical performance could be attributed to the ideal combination of retarded electron recombination and superior energy band structure from the unique N, B–TiO2 particle structure.

Solvothermal Synthesis of Hierarchical TiO2 Microstructures with High Crystallinity and Superior Light Scattering for High-Performance Dye-Sensitized Solar Cells

In this article, hierarchical TiO2 microstructures (HM-TiO2) were synthesized by a simple solvothermal method adopting tetra-n-butyl titanate as the titanium source in a mixed solvent composed of N,N-dimethylformamide and acetic acid. Due to the high crystallinity and superior light-scattering ability, the resultant HM-TiO2 are advantageous as photoanodes for dye-sensitized solar cells. When assembled to the entire photovoltaic device with C101 dye as a sensitizer, the pure HM-TiO2-based solar cells showed an ultrahigh photovoltage up to 0.853 V. Finally, by employing the as-obtained HM-TiO2 as the scattering layer and optimizing the architecture of dye-sensitized solar cells, both higher photovoltage and incident photon-to-electron conversion efficiency value were harvested with respect to TiO2 nanoparticles-based dye-sensitized solar cells, resulting in a high power conversion efficiency of 9.79%. This work provides a promising strategy to develop photoanode materials with outstanding photoelectric conversion performance.

TiO2 SUB-MICROSPHERES AS A BI-FUNCTIONAL SCATTERING LAYER FOR HIGH-PERFORMANCE DYE-SENSITIZED SOLAR CELLS

The sub-microspheres play multiple roles in enhancing dye adsorption and light-scattering to improve the performance of dye-sensitized solar cells (DSSCs). In this work, the well-defined TiO2 sub-microspheres with anatase granular-like nanocrystals are prepared in high yield by combining hydrolytic process with solvothermal treatment. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results indicated that plenty of rhombic nanoparticles with ~ 18 nm diameter having mutual contacts to neighboring nanoparticles were densely self-assembled into sub-microspheres, and abundant mesopores existed in the whole sub-microspheres with superior light scattering ability. The appropriate pore diameter and relatively high specific surface area of the as-obtained sub-microsphere result in a higher dye adsorption. As expected, by using the sub-microspheres as a scattering layer, a higher photovoltaic conversion efficiency of 10.15% is obtained for DSSCs.

Enhancing the Photovoltaic Performance of Perovskite Solar Cells with a Down-Conversion Eu-Complex

Organometal halide perovskite solar cells (PSCs) have shown high photovoltaic performance but poor utilization of ultraviolet (UV) irradiation. Lanthanide complexes have a wide absorption range in the UV region and they can down-convert the absorbed UV light into visible light, which provides a possibility for PSCs to utilize UV light for higher photocurrent, efficiency, and stability. In this study, we use a transparent luminescent down-converting layer (LDL) of Eu-4,7-diphenyl-1,10-phenanthroline (Eu-complex) to improve the light utilization efficiency of PSCs. Compared with the uncoated PSC, the PSC coated with Eu-complex LDL on the reverse of the fluorine-doped tin oxide glass displayed an enhancement of 11.8% in short-circuit current density (Jsc) and 15.3% in efficiency due to the Eu-complex LDL re-emitting UV light (300-380 nm) in the visible range. It is indicated that the Eu-complex LDL plays the role of enhancing the power conversion efficiency as well as reducing UV degradation for PSCs.

High Performance Dye‐Sensitized Solar Cells with Enhanced Light‐Harvesting Efficiency Based on Polyvinylpyrrolidone‐Coated Au–TiO2 Microspheres

Surface plasmon resonance using noble metal nanoparticles is regarded as an attractive and viable strategy to improve the optical absorption and/or photocurrent in dye-sensitized solar cells (DSSCs). However, no significant improvement in device performance has been observed. The bottleneck is the stability of the noble-metal nanoparticles caused by chemical corrosion. Here, we propose a simple method to synthesize high-performance DSSCs based on polyvinylpyrrolidone-coated Au-TiO2 microspheres that utilize the merits of TiO2 microspheres and promote the coupling of surface plasmons with visible light. When 0.4 wt % Au nanoparticles were embedded into the TiO2 microspheres, the device achieved a power conversion efficiency (PCE) as high as 10.49%, a 7.9% increase compared with pure TiO2 microsphere-based devices. Simulation results theoretically confirmed that the improvement of the PCE is caused by the enhancement of the absorption cross-section of dye molecules and photocurrent.