Extremely thin-absorber solar cells offer low materials utilization and simplified manufacture but require improved means to enhance photon absorption in the active layer. Here, we report enhanced-absorption colloidal quantum dot (CQD) solar cells that feature transfer-stamped solution-processed pyramid-shaped electrodes employed in a hierarchically structured device. The pyramids increase, by up to a factor of 2, the external quantum efficiency of the device at absorption-limited wavelengths near the absorber band edge. We show that absorption enhancement can be optimized with increased pyramid angle with an appreciable net improvement in power conversion efficiency, that is, with the gain in current associated with improved absorption and extraction overcoming the smaller fractional decrease in open-circuit voltage associated with increased junction area. We show that the hierarchical combination of micron-scale structured electrodes with nanoscale films provides for an optimized enhancement at absorption-limited wavelengths. We fabricate 54.7° pyramid-patterned electrodes, conformally apply the quantum dot films, and report pyramid CQD solar cells that exhibit a 24% improvement in overall short-circuit current density with champion devices providing a power conversion efficiency of 9.2%.

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Introducing an intermediate section between two metal-insulator-metal plasmonic waveguides with unequal width considerably enhances the transmission spectra of a direct junction. In this paper, we design various junctions based on analytic optimization to obtain maximum power transfer through a junction. Using advantages of quasi-static approximation for subwavelength devices, a pure analytic expression is derived, which leads to broader bandwidth and higher transmittance at given frequency. We achieve zero reflection from 125 to 25 nm width MIM junctions by inserting transition sections consisting of quarter-wavelength and tapered structures between two waveguides. Our analysis and optimization results are numerically validated by the finite-difference time-domain simulation.

A novel wideband microstrip patch antenna with nonuniform transmission line feed is presented using model predictive control. Nonlinear model predictive control (NMPC) is used to achieve a nonuniform transmission line that matches with the microstrip patch antenna. The transmission line is extended using cosine expansion with the impedance differential equation then being used as the dynamic NMPC equation to find the unknown coefficients of that cosine expansion. The transmission line is designed such that the impedance of the input port matches the impedance of the microstrip antenna at the resonance frequency and its adjacent frequencies. The proposed antenna's impedance is 5.15-5.85 GHz. In this bandwidth, the radiation pattern is stable; the cross polarization and back lobe are −30 dB and −20 dB, respectively. The error in the impedance bandwidth is about 4.2%. The simulation and measurement results are considered satisfactory.

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