Hua Zhang

The balance between band structure, composition and defect is essential for improving the optoelectronic properties of ternary and quaternary quantum dots and the corresponding photovoltaic performance. In this work, ascorbic acid (AA) as capping ligand is introduced into the reaction system to prepare green Zn-Cu-In-Se (ZCISe) quantum dots. Results show that the addition of AA can increase the Zn content while decrease In content, resulting in the enlarged band gap, high conduction band energy level and suppressed charge recombination. When AA/Cu ratio is 1, the quantum dots possess the largest band gap of 1.49 eV and the assembled quantum dot sensitized solar cells exhibit superior photovoltaic performance with ~ 17% increment mainly contributed by the dramatically increased current density. The new record efficiency of 10.44% and 13.85% are obtained from the ZCISe cells assembled with brass and titanium mesh based counter electrodes respectively.

Intrinsically weak interaction between oil-soluble quantum dots (QDs) and TiO2 in a direct adsorption process limits QD loading and the performance of QD-sensitized solar cells (QDSCs). Herein, the underlying chemistry and mechanisms governing QD adsorption on TiO2 were studied to improve QD loading and cell performance. Experimental results indicate that solvent polarity plays the crucial role in determining QD loading. Compared with single-component solvents, substantially greater QD loading can be realized at the critical point (CP) of bicomponent solvents, where QDs become metastable and start to precipitate. Through this strategy, average efficiency of 12.24% was obtained for ZCISe QDSCs, which is comparable to those based on the capping ligand induced self-assembly route. This report demonstrates the great potential of bicomponent solvents at the CP for high QD loading and excellent cell performance and presents a platform for assembling functional composites with the use of different nanocrystals and substrates.

Although copper sulfide and/or carbon materials have been utilized in counter electrodes (CEs) due to their good catalytic activity and conductivity, the efficiency of the assembled quantum dot-sensitized solar cells (QDSCs) is still unsatisfactory because of the relatively low photovoltage (V_oc), which is commonly less than 0.7 V. In this study, graphene hydrogels (GHs) compressed onto titanium mesh served as the CE and the assembled CdSeTe QDSCs exhibited a photovoltaic conversion efficiency (PCE) of 9.85% and a V_oc as high as 0.756 V, which increased by 19.0% and 14.9%, respectively, and are higher than those of the conventional CuS on FTO. By incorporating CuS nanoparticles into GH during gelation, the as-prepared GH–CuS CEs show further improved performance and the maximum PCE and V_oc obtained were 10.71% and 0.786 V, respectively. The fill factor of the cells was also continuously increased. The excellent performance of the devices could be attributed to the synergistic effects of the water-rich GH (having a 3D porous structure accompanied by good conductivity) and highly catalytic CuS, reflected from the small series resistance, high catalytic activity, small electron transfer resistance, and stability, which have been confirmed by EIS, Tafel polarization, and CV curves.

A Cu₂S/Ni foam CE has been fabricated via a redox reaction between Ni and Cu ions followed by sulfidation. The as-prepared bendable CE shows superior catalytic activity and conductivity. The assembled flexible CdSe QDSCs exhibit the highest conversion efficiency of 3.55% reported to date.

CdS nanocrystals with a wide variety of shapes including spheres, tetrahedra, and branched and flower-like structures have been conveniently tuned by only changing the amount of trioctylphosphine (TOP) used in a noninjection synthetic approach, in which CdO and S powder were directly used as reactants in paraffin media. The noninjection approach could be facilely scaled up to tens of grams scale in one batch reaction. The shape-controlled growth mechanism could be explained by the TOP-concentration-dependent nuclei structure and monomer concentration. This is further confirmed by the effects of the amount of oleic acid and the Cd/S ratio on the morphology of the obtained CdS nanocrystals. All the CdS nanocrystal samples with different morphologies exhibit good photocatalytic activity for degradation of dyes. The observed lower photocatalytic activity of the sphere-shaped CdS nanocrystals could be ascribed to the higher PL emission efficiency relative to those with other morphologies, which results in low electron–hole separation efficiency. Our reported preparation approach can satisfy the requirements of industrial production bearing the advantage of low-cost, reproducibility and scalability.