Two-dimensional function photonic crystals, in which the dielectric constants of medium columns are the functions of space coordinates 𝑟, are proposed and studied numerically. The band gaps structures of the photonic crystals for TE and TM waves are different from the two-dimensional conventional photonic crystals. Some absolute band gaps and semi-Dirac points are found. When the medium column radius and the function form of the dielectric constant are modulated, the numbers, width, and position of band gaps are changed, and the semi-Dirac point can either occur or disappear. Therefore, the special band gaps structures and semi-Dirac points can be achieved through the modulation on the two-dimensional function photonic crystals. The results will provide a new design method of optical devices based on the two-dimensional function photonic crystals.

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A diamond p-n junction is used to convert the decay energy of 63 Ni source into electrical energy. The selfabsorption effect of the 63 Ni source, the backscatter process and the transport process of beta particles in diamond materials are studied. Then the theoretical maximum of electrical properties and the energy conversion efficiencies of diamond-63 Ni p-n junction batteries are achieved. Finally, a feasible design of 𝑝 + 𝑝 − 𝑛 + junction battery, which has the maximum output power density of 0.42 𝜇W/cm 2 and the optimal device conversion efficiency of 26.8%, is proposed.

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Herein, we investigated the effect of molecular weight (MW) on the efficiency of PDTS-DTffBT based polymer solar cells (PSCs). PDTS-DTffBTs with three different MWs were synthesized by controlling the polymerization conditions. The performance of PSCs improved significantly as the number-average molecular weight (M n) increased from 9 to 36 kDa. Combined with UV–vis absorption and electrochemical cyclic voltammetry measurements, the absorption properties and frontier orbital energy levels of the polymers were estimated, indicating the red-shifted light absorption and up-shifted highest occupied molecular orbital (HOMO) energy level when MW increased. PDTS-DTffBT with high MW also provided increased charge mobility, smoother film surface, and reduced domain size in morphology of the PDTS-DTffBT:PC71BM active layer. The performance of PDTS-DTffBT based PSCs was improved owing to these MW related properties, and both short circuit current density (J SC) and power conversion efficiency (PCE) went up significantly with increasing MW. The best PCE of 6.40% was achieved by the devices based on the PDTS-DTffBT with a M n value of 36 kDa.