The power conversion efficiencies (PCEs) of PbS quantum dot sensitized solar cells (QDSCs) reported are typically below 6%. This poor efficiency is mainly derived from the serious charge recombination in internal QDs and at the interface of QDs/TiO2/electrolyte. In this work, PbS/CdS QDs with a core/shell structure, which were used as the photosensitizer to fabricate sensitized solar cells, were prepared through the ion exchange method. With the reduced trapping state defects on the surface of the PbS QDs and resulting effective suppression of adverse charge recombination, the PbS/CdS QD-based cells have been improved remarkably in comparison with the pristine PbS-based QDSCs. By optimization of the thickness of the CdS shell, a PCE of 7.19% under one full sun illumination was obtained on the fabricated devices, which is among the best performances for liquid-junction PbS QDSCs.

Limited by the volatilization and leakage of liquid electrolytes, the long-term stability of liquid-junction quantum dot sensitized solar cells (QDSCs) remains a main challenge for the application of QDSCs. Herein, a polyelectrolyte with superior water-absorbing and water-holding capacity, sodium polyacrylate (PAAS), was attempted to gelate conventional aqueous polysulfide electrolytes to construct quasi-solid-state QDSCs. PAAS gel electrolytes have a comparable conductivity with liquid polysulfide electrolytes. Meanwhile, the PAAS gel could penetrate readily into the framework of mesoporous TiO2 film electrodes due to the strong coordination ability of carboxylate groups on PAAS polymer chains with metal ions. Benefited from the high conductivity of the PAAS gel and its perfect contact with the TiO2 surface, an impressive photovoltaic performance with a power conversion efficiency of 8.54% in one full sunlight, which is among the best performance for QDSCs, was achieved for CdSeTe QDSCs. Furthermore, the light-soaking stability of the resulting cell devices is significantly improved in comparison with that of the conventional aqueous polysulfide electrolyte based ones.

Besides the relatively high redox potential of the adopted S2−/Sn2− polysulfide redox couple electrolyte, the parasitic charge recombination process is another significant factor that limits the open-circuit voltage and consequent power conversion efficiency (PCE) of quantum dot sensitized solar cells (QDSCs). Herein, we report a facile method to modify the polysulfide electrolyte with the addition of polyethylene glycol (PEG) additives to suppress the charge recombination occurring at the TiO2/QDs/electrolyte interfaces. Impedance spectroscopy and open circuit voltage decay (OCVD) measurements reveal that the PEG additive in the polysulfide electrolyte reduces interfacial recombination when compared with the conventional polysulfide electrolyte in the absence of the PEG additive. A dramatic enhancement of PCE from 5.80% to 6.74% was observed with the introduction of 15 wt% PEG in the polysulfide electrolyte in CdSe based QDSCs. Moreover, the PEG additive also improves the photovoltaic performance stability of the resultant cells.

Surface trap defects are the limited factor for quantum dots (QDs) application in solar cells. The trapping states can be efficiently suppressed by coating a shell of wider band gap material around the core QDs. We choose CdSe0.65Te0.35 (simplified as CdSeTe) as a model core material, and CdS shell was then overcoated around the CdSeTe core QD to decrease surface defect density and to increase the stability of the core QDs. By optimizing the thickness of the CdS shell, the power conversion efficiency (PCE) of the CdSeTe/CdS quantum dots sensitized solar cells (QDSCs) is enhanced by 13% in comparison with that of plain CdSeTe QDSCs. Transient absorption (TA), incident-photo-to-carrier conversion efficiency (IPCE), open-circuit voltage decay (OVCD), and electrochemical impedance spectroscopy (EIS) measurements confirmed the suppressed charge recombination process in internal QDs and QD/TiO2/electrolyte interfaces with the overcoating of CdS shell around CdSeTe core QDs. With the further overcoating of a-TiO2 and SiO2 barrier layers around the QD-sensitized photoanode, the PCE of champion CdSeTe QDSCs achieved 9.48% (Jsc = 20.82 mA/cm2, Voc = 0.713 V, FF = 0.639) with average PCE 9.39 ± 0.09% under AM 1.5 G one full sun illumination.

Facile detection of dopamine (DA) in biological samples for diagnostics remains a challenge. This paper reported an effective fluorescent sensor based on adenosine capped CdSe/ZnS quantum dots (A-QDs) for highly sensitive detection of DA in human urine samples. In this assay, adenosine serves as a capping ligand or stabilizer for QDs to render high-quality QDs dispersed in water, and as a receptor for DA to attach DA onto the surface of A-QDs. DA molecules can bind to A-QDs via non-covalent bonding, leading to the fluorescence quenching of A-QDs due to electron transfer. The A-QDs based fluorescence probe showed a limit of detection (LOD) of ca. 29.3 nM for DA detection. This facile method exhibited high selectivity and anti-interference in the presence of amino acid, ascorbic acid (AA), uric acid (UA) and glucide with 100-fold higher concentration in PBS solution. Furthermore, it was also successfully used in the detection of DA in the human urine samples with quantitative recoveries (94.80–103.40%).

The quenched fluorescence of quantum dots (QDs) attached to TiO2 nanoparticles was selectively switched on by biothiols through ligand replacement, which makes it feasible for facilely sensing biothiols based on the fluorescence turn on mechanism. The present sensor exhibited excellent selectivity and high sensitivity. Furthermore, a novel fluorescent indicating paper was constructed by immobilizing the probe on filter paper to visually detect biothiols in which only a UV lamp was used.

To overcome the low emission efficiency and poor photo and colloidal stability of quantum dots (QDs) prepared in aqueous media, the main challenge is to find suitable capping reagents to obtain stable QD/ligand complexes. Adenosine 5′-monophosphare (AMP) appears very promising for the stabilization and the further functionalization of QDs because AMP has multiple functionalities that can chelate metal cations. Herein, we synthesized high-quality CdTe/CdS core/shell nanostructures in aqueous media, in which AMP and thiopropionic acid (MPA) acting as dual stabilizing agents were introduced directly on the surface of QDs. With the combination of AMP and MPA ligands, it was found that dual ligands could accelerate the reaction kinetics, accompanied by possessing high emission efficiency of QDs. The prepared water-soluble AMP/MPA-QDs exhibit narrow size distribution and nearly spherical morphology. Most importantly, the resultant water-soluble AMP/MPA-QDs exhibit superior photo and colloidal stability, solving the problem of deterioration for biological applications. To demonstrate the targeting capability of QDs, we have used folate-receptor targeting to show good selectivity to tumor cells.

Limited by the volatilization and leakage of liquid electrolytes, the long-term stability of liquid-junction quantum dot sensitized solar cells (QDSCs) remains a main challenge for the application of QDSCs. Herein, a polyelectrolyte with superior water-absorbing and water-holding capacity, sodium polyacrylate (PAAS), was attempted to gelate conventional aqueous polysulfide electrolytes to construct quasi-solid-state QDSCs. PAAS gel electrolytes have a comparable conductivity with liquid polysulfide electrolytes. Meanwhile, the PAAS gel could penetrate readily into the framework of mesoporous TiO2 film electrodes due to the strong coordination ability of carboxylate groups on PAAS polymer chains with metal ions. Benefited from the high conductivity of the PAAS gel and its perfect contact with the TiO2 surface, an impressive photovoltaic performance with a power conversion efficiency of 8.54% in one full sunlight, which is among the best performance for QDSCs, was achieved for CdSeTe QDSCs. Furthermore, the light-soaking stability of the resulting cell devices is significantly improved in comparison with that of the conventional aqueous polysulfide electrolyte based ones.

The power conversion efficiencies (PCEs) of PbS quantum dot sensitized solar cells (QDSCs) reported are typically below 6%. This poor efficiency is mainly derived from the serious charge recombination in internal QDs and at the interface of QDs/TiO2/electrolyte. In this work, PbS/CdS QDs with a core/shell structure, which were used as the photosensitizer to fabricate sensitized solar cells, were prepared through the ion exchange method. With the reduced trapping state defects on the surface of the PbS QDs and resulting effective suppression of adverse charge recombination, the PbS/CdS QD-based cells have been improved remarkably in comparison with the pristine PbS-based QDSCs. By optimization of the thickness of the CdS shell, a PCE of 7.19% under one full sun illumination was obtained on the fabricated devices, which is among the best performances for liquid-junction PbS QDSCs.

Besides the relatively high redox potential of the adopted S2−/Sn2− polysulfide redox couple electrolyte, the parasitic charge recombination process is another significant factor that limits the open-circuit voltage and consequent power conversion efficiency (PCE) of quantum dot sensitized solar cells (QDSCs). Herein, we report a facile method to modify the polysulfide electrolyte with the addition of polyethylene glycol (PEG) additives to suppress the charge recombination occurring at the TiO2/QDs/electrolyte interfaces. Impedance spectroscopy and open circuit voltage decay (OCVD) measurements reveal that the PEG additive in the polysulfide electrolyte reduces interfacial recombination when compared with the conventional polysulfide electrolyte in the absence of the PEG additive. A dramatic enhancement of PCE from 5.80% to 6.74% was observed with the introduction of 15 wt% PEG in the polysulfide electrolyte in CdSe based QDSCs. Moreover, the PEG additive also improves the photovoltaic performance stability of the resultant cells.