Infrared‐absorbing colloidal quantum dots (IR CQDs) are materials of interest in tandem solar cells to augment perovskite and cSi photovoltaics (PV). Today's best IR CQD solar cells rely on the use of passivation strategies based on lead iodide; however, these fail to passivate the entire surface of IR CQDs. Lead chloride passivated CQDs show improved passivation, but worse charge transport. Lead bromide passivated CQDs have higher charge mobilities, but worse passivation. Here a mixed lead‐halide (MPbX) ligand exchange is introduced that enables thorough surface passivation without compromising transport. MPbX–PbS CQDs exhibit properties that exceed the best features of single lead‐halide PbS CQDs: they show improved passivation (43 ± 5 meV vs 44 ± 4 meV in Stokes shift) together with higher charge transport (4 × 10‐2 ± 3 × 10‐3 cm2 V‐1 s‐1 vs 3 × 10‐2 ± 3 × 10‐3 cm2 V‐1 s‐1 in mobility). This translates into PV devices having a record IR open‐circuit voltage (IR Voc) of 0.46 ± 0.01 V while simultaneously having an external quantum efficiency of 81 ± 1%. They provide a 1.7× improvement in the power conversion efficiency of IR photons (>1.1 µm) relative to the single lead‐halide controls reported herein.

The wormlike-chain model is commonly used to describe the statistical properties of DNA and liquid-crystal polymers. Following the Green's function approach, here we present the confinement free energy, compression force, and conformational properties of a wormlike chain in slit confinement over a full range of chain lengths (from rodlike, to semiflexible, and to flexible) and confinement widths (from wide to narrow). Some of these properties have previously been covered in the extreme asymptotic limits of polymer chain lengths and slit widths. The current calculation yields the numerical results that navigate the crossover between these extremes and hence provides a comprehensive picture over the entire parameter space for an ideal wormlike chain with no excluded-volume effects.

A key model to support the understanding of the forced extension of real polymers is the wormlike chain under a stretching potential, which is characterized by two basic parameters, the stiffness and the external force. Here, adopting commonly used theoretical and computational approaches, we provide a high-precision numerical solution over a large range of the parameter space. The validity of previous theoretical studies and the current work, for both extension− force relations and the mean square end-to-end distance projected along the direction perpendicular to the stretching, is critically examined using the numerical data as the benchmark.

When a semiflexible polymer wraps around a solid cylinder with a radius comparable to the persistence length, it displays a helical conformation. What is the confinement free energy of this particular conformation and what is the pitch, the basic geometric measure of the helix, as a function of the persistence length to cylinder radius ratio? Here we explore these on the basis of a standard wormlike-chain model, by using the Green's function approach in statistical physics and numerical computation of the resulting differential equation. In the asymptotic limits of small and large cylinder radius, a power-law scaling relationship is also established from a scaling argument and from the exact solution to the theoretical model. The results from the calculation agree well with experimental data, computer-simulation data, and a previous theoretical estimate. The work sheds light on recent developments in the area of single-walled carbon nanotubes wrapped by various types of long polymers.