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To absorb the photons below the band-gap energy effectively, we proposed a quantum dot (QD) photocell modeled by multi-level system for the quantum yields and photo-to-charge efficiency limits. The theoretical results show the quantum yields are enhanced as compared to the single band-gap solar cell, and the photo-to-charge efficiencies are larger than Shockley and Queisser efficiency in the same absorbed spectrum. What's more, at the room temperature the efficiency limits are well beyond 63% achieved by Luque and Marti (Ref\cite{26}) due to absorbing the low-energy photons via two sub-bands in this proposed photocell system. The achievements may reveal a novel theoretical approach to enhance the QD photocell performance modeled a multi-level absorbing photons system., Comment: 13 pages, 6 figures

The radiative recombination of electron-hole pairs represents a great challenge to the photon-to-charge efficiency in photocell. In this paper, we visit the radiative recombination rate (RRR) in a quantum photocell with or without three dipole-dipole coupled electron donors. The results show that different gaps play the same roles while the ambient temperatures play different roles in the suppressed RRR with or without three dipole-dipole coupled electron donors. What's more, the dipole-dipole coupling strength J can greatly inhibit the RRRs with three dipole-dipole coupled electron donors, which indicates the quantum coherence generated by three coupled donors is an efficient approach to suppress RRR, and it is different from the quantum coherence mentioned by Marlan O. Scully [PRL 104, 207701 (2010)]. This presented scheme may propose some regulating strategies for efficient conversion efficiency via the suppressed RRR., Comment: 10 pages, 4 figures. arXiv admin note: substantial text overlap with arXiv:1902.01804

The radiative recombination of electron-hole pairs represents a great challenge to the photon-to-charge efficiency in the photocell. In this paper, we investigate how to suppress radiative recombination rate (RRR) in a proposed quantum photocell with three dipole-dipole coupled and uncoupled electron donors. The results showed that the RRR could be suppressed in this photocell with three uncoupled electron donors but be enhanced with three dipole-dipole coupled electron donors by the ambient circumstance temperatures, and the increasing energy gap in the donors, the decreasing gap between the donors and acceptor inhabited the RRR with three dipole-dipole both coupled and uncoupled electron donors. When the photocell was manipulated by the electrostatic dipole-dipole coupling strength J at room temperature, the RRR was suppressed to a smaller minimum by the gap between the donors and acceptor than those by different gaps in the donors. These suppressed strategies for RRR point out some significant ways to increase the photon-to-charge efficiency and deserve the further experimental verification., Comment: 10 pages, 8 figures

Selective Harmonic Elimination Pulse Width Modulation (SHEPWM) is an important technique to solve PWM problems, which control the output voltage of an inverter via selecting appropriate switching angles. Based on the Rational Univariate Representation (RUR) theory for solving polynomial systems, the paper presents an algorithm to compute a "nearly parametric" solution to a SHEPWM problem. When the number of switching angles N is fixed, a "nearly parametric" solution can be considered as functions of the modulation index m. So we can adapt the amplitude of the output voltage with the same source voltage by changing the modulation index. When m is given as a specific value, complete solutions to the SHEPWM problem can be obtained easily using univariate polynomial solving. Compared with other methods, m is considered as a symbolic parameter for the first time, and this can help avoid totally restarting when m changes. The average time for computing complete solutions associated to 460 modulation indexes based on a "nearly parametric" solution when N=5 is 0.0284s, so the algorithm is practical. Three groups of switching angles associated to N=5, m=0.75 is simulated in MATLAB, and it verifies the algorithm's correctness.