Stimuli responsive self‐folding structures with 2D layered materials (2DLMs) are important for flexible electronics, wearables, biosensors, bioelectronics, and photonics. Previously, strategies have been developed to self‐fold 2D materials to form various robots, sensors, and actuators. Still, there are limitations with scalability and a lack of design tools to obtain complex structures for reversible actuation, high integration, and reliable function. Herein, a mass‐producible strategy for creating monolayer graphene‐based reversible self‐folding structures using either gradient or differentially cross‐linked films of a negative epoxy photoresist widely used in microfluidics and micromechanical systems, namely, SU8 is demonstrated. Wafer‐scale patterning and integration of complex and functional devices in the form of rings, polyhedra, flowers, and bidirectionally folded origami birds are achieved. Also, gold (Au) electrodes to realize functional graphene–Au Schottky interfaces with enhanced photoresponse and 3D angle sensitive detection are integrated. The experiments are guided and rationalized by theoretical methods including coarse‐grained models, specifically developed for the tunable mechanics of this photoresist that simulate the folding dynamics, and finite element method (FEM) electromagnetic simulations. This work suggests a comprehensive framework for the rational design and scalable fabrication of complex 3D self‐actuating optical and electronic devices through the folding of 2D monolayer graphene.

Colloidal quantum dots (CQDs), are a promising candidate material for realizing colored and semitransparent solar cells, due to their band gap tunability, near infrared responsivity and solution-based processing flexibility. CQD solar cells are typically comprised of several optically thin active and electrode layers that are optimized for their electrical properties; however, their spectral tunability beyond the absorption onset of the CQD layer itself has been relatively unexplored. In this study, we design, optimize and fabricate multicolored and transparent CQD devices by means of thin film interference engineering. We develop an optimization algorithm to produce devices with controlled color characteristics. We quantify the tradeoffs between attainable color or transparency and available photocurrent, calculate the effects of non-ideal interference patterns on apparent device color, and apply our optimization method to tandem solar cell design. Experimentally, we fabricate blue, green, yellow, red and semitransparent devices and achieve photocurrents ranging from 10 to 15.2 mA/cm² for the colored devices. We demonstrate semitransparent devices with average visible transparencies ranging from 27% to 32%, which match our design simulation results. We discuss how our optimization method provides a general platform for custom-design of optoelectronic devices with arbitrary spectral profiles.

Colloidal quantum dot (CQD) solar cells have benefited from rapidly rising single-junction efficiencies in recent years and have shown promise in multijunction and color-tuned applications. However, within the context of next-generation solar cells, CQD photovoltaics still have an efficiency deficit compared to mature technologies. Here, we use one-dimensional optoelectronic solar cell simulations to show that much of this efficiency deficit in the highest-performing PbS CQD solar cells can be attributed to the hole transport layer (HTL). We find that increasing both the doping density and, counterintuitively, the electron mobility in this layer should have the largest impact on performance, attributed to the nontrivial role that the HTL plays in photon absorption. We use stoichiometry control through sulfur infusion of the standard CQD HTL materials to improve the carrier mobilities and doping density. This work resulted in a clear performance improvement, to 10.4% power conversion efficiency in the best device.

Although record efficiencies in colloidal quantum dot (CQD) solar cells continue to increase, they are still demonstrated on impractically small-area devices. Concentrators can effectively enlarge the active area, allowing scaled-up energy harvesting. Here, we present an economical and scalable method to fabricate compact concentrators made from polydimethylsiloxane using 3D-printed molds, which are directly bonded to CQD solar cells. The resulting integrated systems deliver more than a 20-fold increase in photocurrent and power, as well as significant open circuit voltage enhancements, over the original cells. We use the integrated systems to identify limiting factors in CQD solar cell operation under high irradiance. Our method could pave the way to making practical high-power solution-processed solar cells.

The displacements for |P> polarization (electric field parallel to the plane-of-incidence) and |S> polarization (electric field perpendicular to the plane-of-incidence) induced by the spin Hall effect of light reflected from a magnetic cobalt thin film have been investigated. The significant differences from those of an air-glass interface are attributed to the special complex permittivity and refractive index of the cobalt film. The real part of the complex refractive index has more influence on displacements for |P> polarization than for |S> polarization. There also exists a particular incident angle corresponding to the zero displacement for |P> polarization. It shifts from 52° to 76° when the real part rises from 1.0 to 4.0. For both |P> and |S> polarizations, the maximal displacements rapidly rise with the decrease of the imaginary part. Our simulations further demonstrate that polarization-insensitive spin separations can be realized by choosing the medium with an optimal permeability.