SnO2 modified mesoporous ZrO2 is used to replace the mesoporous TiO2 layer and serves as a kind of mesoporous electron-transport layer during the low-temperature fabrication of mesoscopic perovskite solar cells that are based on carbon electrode. X-ray/ultraviolet photoelectron spectroscopy studies and electrical test observe that SnO2 modification brought down the work function while increasing the conductivity of the mesoporous ZrO2. Transient photovoltage/photocurrent decay curves, impedance spectroscopy, and photoluminescence mapping show that after the bottom layer of ZrO2 is modified by SnO2, the charge extraction process is accelerated while recombination is retarded. This modification helps to increase the power conversion efficiency from 4.70 (±0.85)% to 10.15 (±0.35)%, along with the optimized efficiency at 13.37% (AM1.5G, 100 mW/cm2) for the low-temperature devices. In addition, the effects of modification layers of SnO2 on the power conversion properties are carefully studied. This study shows that SnO2 modified mesoporous ZrO2 could serve as an efficient electron-transport layer for the low-temperature mesoscopic devices.
A symmetry-based hybrid precoder and combiner is a high spectral efficiency structure in millimeter-wave (mmWave) massive multiple-input multiple-output (mMIMO) non-orthogonal multiple access (NOMA) system. To improve the spectral efficiency of the mmWave mMIMO-NOMA system, we first propose a user grouping scheme to suppress the strong inter-user interference caused by NOMA, then the hybrid precoder based on user channel alignment and the zero-forcing algorithm is constructed to further improve the signal-to-interference-plus-noise ratio (SINR) of the receiver. Subsequently, the non-convex spectral efficiency optimization problem is transformed into a convex optimization problem of inter-cluster power allocation and the closed-form solution for the optimal power under the minimum rate constraint is obtained by solving the KKT condition to further improve the spectral efficiency. The simulation results show that the proposed scheme can achieve higher spectral efficiency compared to orthogonal multiple access (OMA), fixed power allocation (FPA), K-means, and cluster head selection (CHS).
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