I-Ping Liu

Highly electrocatalytic counter electrodes based on carbon black for cobalt(III)/(II)-mediated dye-sensitized solar cells

While carbon black (CB) is an ordinary, commercial and low-cost carbonaceous material, it displays great potential as an alternative to noble metals and conductive polymers in terms of a counter electrode catalyst for dye-sensitized solar cells (DSSCs) using a Co(bpy)32+/3+ (bpy = 2,2′-bipyridine) redox couple. First, the electrocatalytic activity of this low crystalline material in relation to the cobalt-based redox reaction is carefully studied. The experimental results show that both the heat treatment and the amount of CB loading are key parameters affecting the electrochemical behavior of the resultant CB thin films. A well-prepared CB thin film exhibits better electrocatalysis than sputtered platinum does. This CB film demonstrates its ability to replace common platinum as an efficient counter electrode in DSSCs using a Co(bpy)32+/3+ electrolyte. This material is even more suitable than platinum for fabrication of semitransparent counter electrodes for bifacial photovoltaic applications. Most importantly, a highly efficient Y123-sensitized solar cell is assembled using a CB thin film, revealing a power conversion efficiency of 8.81% without any striking mass transport obstruction. The feasibility of this cost-effective CB material for utilization in DSSCs is definitely verified.

Performance Enhancement of Quantum-Dot-Sensitized Solar Cells by Potential-Induced Ionic Layer Adsorption and Reaction

Successive ionic layer adsorption and reaction (SILAR) technique has been commonly adopted to fabricate quantum-dot-sensitized solar cells (QDSSCs) in the literature. However, pore blocking and poor distribution of quantum dots (QDs) in TiO2 matrices were always encountered. Herein, we report an efficient method, termed as potential-induced ionic layer adsorption and reaction (PILAR), for in situ synthesizing and assembling CdSe QDs into mesoporous TiO2 films. In the ion adsorption stage of this process, a negative bias was applied on the TiO2 film to induce the adsorption of precursor ions. The experimental results show that this bias greatly enhanced the ion adsorption, accumulating a large amount of cadmium ions on the film surface for the following reaction with selenide precursors. Furthermore, this bias also drove cations deep into the bottom region of a TiO2 film. These effects not only resulted in a higher deposited amount of CdSe, but also a more uniform distribution of the QDs along the TiO2 film. By using the PILAR process, as well as the SILAR process to replenish the incorporated CdSe, an energy conversion efficiency of 4.30% can be achieved by the CdSe-sensitized solar cell. This performance is much higher than that of a cell prepared by the traditional SILAR process.

High-performance printable electrolytes for dye-sensitized solar cells

High-performance quasi-solid-state electrolytes with printable characteristics are developed herein for dye-sensitized solar cells (DSSCs). The printable electrolytes are prepared based on a 3-methoxypropionitrile liquid electrolyte containing I−/I3− redox couples. Poly(ethylene oxide) (PEO) and poly(vinylidene fluoride) (PVDF) are utilized as agents to regulate the viscosity and properties of the electrolyte pastes; furthermore, TiO2 nanoparticles are used as a filler to enhance the performance of the electrolytes. The results show that PEO is a required material to prepare the electrolyte pastes for operation by a printing process. However, if only PEO is utilized, the conversion efficiency of the corresponding cell (7.65%) is much lower than that of the liquid one (8.34%). By introducing PVDF as a co-regulating agent, the resultant cell can achieve an efficiency of 8.32% similar to that of the liquid cell, mainly attributed to the decrease of charge transfer resistance at the electrolyte/Pt counter electrode interface. In addition, if 4 wt% TiO2 nanoparticles are introduced as fillers into the printable electrolyte, the cell efficiency can be further increased to 8.91%. By applying this printable electrolyte to a sub-module cell, a conversion efficiency of 6.45% is achieved. The DSSCs prepared by the printing process are stable under a long-term stability test at 60 °C.

Highly electrocatalytic carbon black/copper sulfide composite counter electrodes fabricated by a facile method for quantum-dot-sensitized solar cells

A facile and cost-effective method is proposed herein to fabricate highly electrocatalytic carbon black/copper sulfide (CB/CuXS) composite counter electrodes for quantum-dot-sensitized solar cells (QDSSCs). In brief, mesoporous CB thin films and copper salts are first deposited on FTO substrates by a spin-coating process; a sulfidation treatment is then conducted to facilitate accumulations of CuXS catalysts in the mesoporous structure. Experimental results illustrate that during the sulfidation, an ion exchange reaction and a reduction of Cu(II) to Cu(I) take place simultaneously, and that the obtained CuXS catalyst possesses a nonstoichiometric phase. The electrochemical properties of the resultant composite films are carefully investigated. The results show that the electrocatalytic activity of the CB/CuXS films related to the polysulfide redox reaction is much superior to that of common platinum. Compared to a solar cell equipped with a solution-processed CuS counter electrode, the QDSSC using a composite film prepared only by a single spin-coating displays similar photovoltaic performance. Furthermore, increasing the coating times can lead to improvements both in the electrocatalytic activity of the CB/CuXS films and in the cell performance of the relevant QDSSCs. When CdS/CdSe sensitizers are employed, the QDSSC using a CB/CuXS counter electrode fabricated with three coating times demonstrates a conversion efficiency of 5.62% under 1 sun irradiation.

Charge transport of CdS/CdSe Co-sensitized solar cells

CdS, CdSe sensitized solar cells were investigated with excitation-wavelength-dependent, time-resolved photoluminescence technique and charge transport model. This approach is helpful to design semiconductor-sensitized and other types of solar cells.