A quartz crystal microbalance (QCM) was applied to study the kinetics of adsorption of nearly monodisperse, high molecular weight polystyrene (PS) onto gold from dilute solutions at the condition. An analysis of QCM frequency shifts during adsorption, based on the mechanical resonance theory of Kanazawa et al.,24,28 predicts that the shift is proportional to a linear combination of the adsorbed layer depth and the polymer coverage. A method is proposed to extract the portion of the shift due to the coverage, which enables one to construct the expected isotherm from equilibrium frequency shifts. The effects on the adsorption kinetics of polymer molecular weight and of bulk polymer concentration were studied systematically. The data were compared to a preliminary theory by de Gennes6,6 which assumes that an adsorbed layer relaxes instantaneously during adsorption and that the adsorption rate is controlled by end-in reptation of chains across the partially developed layer. The data deviate from the theory in two ways. Firstly, the adsorption process has a much longer time scale than any realistic estimate based on the end-in reptation mechanism, and this time scale is insensitive to molecular weight, which is at odds with prediction. Secondly, the transmission coefficient of a partially formed adsorbed layer clearly depends on how the layer was formed, suggesting that memory effects play an important role in the layer formation process. In toto, the kinetic data suggest that long time scale surface rearrangements insensitive to molecular weight control the adsorption rate in this system.

Colloidal quantum dots (CQDs) have a large specific surface area and a complex surface structure. Their properties in diverse optoelectronic applications are largely determined by their surface chemistry. Therefore, it is essential to investigate the surface chemistry of CQDs for improving device performance. Herein, we realized an efficient surface chemistry optimization of lead sulfide (PbS) CQDs for photovoltaics by annealing the CQD solution with concentrated lead halide ligands after the conventional solution-phase ligand exchange. During the annealing process, the colloidal solution was used to transfer heat and create a secondary reaction environment, promoting the desorption of electrically insulating oleate ligands as well as the trap-related surface groups (Pb-hydroxyl and oxidized Pb species). This was accompanied by the binding of more conductive lead halide ligands on the CQD surface, eventually achieving a more complete ligand exchange. Furthermore, this strategy also minimized CQD polydispersity and decreased aggregation caused by conventional solution-phase ligand exchange, thereby contributing to yielding CQD films with twofold enhanced carrier mobility and twofold reduced trap-state density compared with those of the control. Based on these merits, the fabricated PbS CQD solar cells showed high efficiency of 11% under ambient conditions. Our strategy opens a novel and effective avenue to obtain highefficiency CQD solar cells with diverse band gaps, providing meaningful guidance for controlling ligand reactivity and realizing subtly purified CQDs.

Chemical surface treatment of colloidal quantum dots (CQDs) by phase-transfer ligand-exchange (PTLE) is essential to implement highly densified, well-passivated CQD films for optoelectronic applications, such as infrared photovoltaics, light-emitting diodes, and photodetectors. PTLE, however, involves parallel and interactional processes of ligand exchange, phase transfer, and surface passivation of CQDs, which render the optimization of PTLE still challenging. Herein, we explored the action mechanism of a widely used additive, ammonium acetate (AA), on the PTLE of PbS CQDs to recognize the dynamic balance during the PTLE process and its impact on the performance of colloidal quantum dot solar cells (CQDSCs). Our research definitely shows that the AA additive can modify the dynamics of PTLE by participating in all of the three processes, and the amount of AA significantly influences the defect passivation and colloidal stability of PbS CQDs. At an appropriate concentration (∼50 mM) of AA, PbS CQDs are well iodide-passivated by PTLE, and the fabricated CQDSCs achieve a power conversion efficiency (PCE) of ∼10% associated with improved carrier transport and reduced trap-assisted carrier recombination. However, excessive AA causes trace residual AA on the CQD surface, resulting in the insufficient surface passivation of PbS CQDs and trap issues of CQDSCs. The double-edged sword effect of the AA additive on PTLE, demonstrated in our work, suggests that realizing a dynamic balance of different processes during PTLE is crucial for further performance promotion of CQDSCs.

These anticancer drug-loaded poly(carbonate-ester) nanospheres showed the potential as drug delivery systems for cancer therapy.

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