Abstract Preparing large areas of graphene on textured silicon is necessary for the industrialization of graphene/silicon solar cells. However, many passivation films with insulating properties prepared by the solution method are not applicable for the textured structures as the insulation areas are easily formed at the bottom of the pyramid. In this paper, we prepare large-area vertical graphene nanowalls (VGNWs) on textured c-Si by plasma-enhanced chemical vapor deposition (PECVD) and introduce conductive-passivating poly(3,4-ethylenedioxythiophene) (PEDOT):Nafion composite thin films to modify the textured VGNWs/Si Schottky junction. The formation of insulation areas was avoided. Moreover, the reflectivity was reduced to less than 7% as the superposition of textured structures and PEDOT:Nafion film. After applying an interfacial layer of Al 2 O 3 , the cell efficiency was increased to 11.75%, with a large active area of 0.64 cm 2 . This work will promote the industrialization of VGNWs/Si solar cells.
The dark-ring white-eye square super-lattice pattern was studied
in dielectric barrier discharge system for the first time. Each unit
cell of the pattern consisted of a central bright spot surrounded
by a dark ring. The structure of dark ring around the center bright
spot was similar to the white-eye, which was called the dark-ring
white-eyes. The spatial-temporal dynamics of the dark-ring white-eye
square super-lattice pattern was investigated by high speed frame
camera (HSFC). The results showed that the dark-ring white-eye square
super-lattice pattern was an interleaving of four different sub-structures.
The discharge sequence was center bright dot-bright dot halo-vertex
square-vertex connection in each half voltage cycle. The formation
mechanism of dark-ring white-eye square super-lattice pattern and
dark ring was explained by surface charges theory.
We report on the study of moving filaments in a honeycomb pattern in a dielectric barrier discharge system using photomultipliers, a high-speed video camera, and a spectrometer. The honeycomb pattern bifurcates from the hexagonal super-lattice pattern with increasing voltage. It is found that the honeycomb framework is composed of filaments with irregular reciprocating motion, which indicates that the honeycomb framework results from statistical self-organization. The spatiotemporal dynamics show that the pattern consists of three different sub-lattices. The plasma parameters (molecular vibrational temperature and electron density) of the pattern, determined from the optical emission spectra, show that different sub-lattices are in different plasma states. Based on these measurements, the mechanism of the movement of filaments is analyzed briefly.
The linear-zigzag transition is observed and studied in dielectric barrier discharge with rectangular frames for the first time by two photomultipliers, an intensified charge-coupled device, and a high-speed video camera. The unstable linear spot pattern transforms into a stable zigzag superlattice pattern with increasing voltage. The zigzag superlattice pattern is made up of dim spots at each corner, light spots between dim spots, and a zigzag line which is composed of moving spots and zigzag halos. All the spots in the linear spot pattern discharge simultaneously, and they have equal electric quantities, while the discharge sequence in the zigzag superlattice pattern is light spots, dim spots, halos, moving spots, and electric quantities of light spots are more than that of dim spots. The difference in the electric quantities leads to the formation of zigzag halos. In a word, the zigzag superlattice pattern results from unequal wall charge quantities of different sublattices and statistical self-organization of moving spots.
We report a square superlattice pattern with discharge holes due to direction-selective surface discharges (SDs) in a dielectric barrier discharge system for the first time. The instantaneous images with an exposure time of 10 μs (half cycle of voltage) taken using a high-speed video camera show that the directions of surface discharges (SDs) of the small spots are selective, which are different from the directions of SDs of the large spots diffused in all directions. In each positive half cycle of voltage, the graphs captured using an intensified charge-coupled device show that the large spot discharges after the small spots and locates at the center of the square formed by the SDs induced by small spots but not their cross point. In each negative half cycle of voltage, the large spots discharge before the small spot and press the SD of the small spot to stretch along the midperpendicular of two adjacent large spots. In a word, the direction-selective surface discharges play a crucial role for the formation of the pattern with the discharge holes in the dielectric barrier discharge system.
We report on a square super-lattice pattern by interaction of surface discharge with the applied voltage increasing in a dielectric barrier discharge system. The pattern consists of bright spots, bright lines, and dim spots. The spatio-temporal dynamics of the pattern is studied by photomultiplier (PMT), high speed video camera and normal camera. Results show that the bright spots discharge several times during each half cycle and they are formed by volume discharge (VD), bright line was formed by superposition of the surface discharges (SDs) over a long period of time, and the dim spots are consist of four small spots. The dim spots are formed by the repulsion of SDs. The light intensity of the bright and dim spots of the patch was compared and it was found that the ratio of the light intensity of the bright spot to the dark spot was about 10. The measurement of the emission spectroscopy show the parameters of the bright spots are different from that of the bright lines and dim spots, the discharge type of bright spots an dim spots is different, and reflects that the dim spots are formed by the interaction of SDs. The formation of the pattern is explained by the wall charge theory.
Abstract Using plasma-enhanced chemical vapor deposition (PECVD) to directly grow graphene nanowalls (GNWs) on silicon to preparate the solar cells is compatible with current industrial production. However, many defects in the GNWs hinder improvement of the power conversion efficiency (PCE) of solar cells. In this work, we found that the defects in GNWs can be reduced under the condition of keeping the appropriate sheet resistance of GNWs by simultaneously reducing the growth temperature and increasing the growth time. Then, a PCE of 3.83% was achieved by minimizing the defects in the GNWs under the condition of ensuring adequate coverage of GNWs on bare planar silicon. The defects in GNWs were further reduced by adding a poly(3,4-ethylenedioxythiophene) (PEDOT):Nafion passivation coating, and the PCE was significantly improved to 10.55%. Our work provides an innovative path and a simple approach to minimize the defects in graphene grown directly on silicon for high-efficiency solar cells.
Pattern formation and self-organization are fascinating phenomena found widely in nature and in laboratory environment such as dielectric barrier discharge (DBD). Significant efforts have been made to explain the dynamic pattern formation. In DBD, the formation of side discharges is generally supposed to be a key factor responsible for diversity and spatial-temporal symmetry breaking of pattern formation. However, it is still not clear how such discharges are induced. Here, we present the observations of side discharges in a filamentary dielectric barrier discharge from both numerical simulations and experiments. Two-dimensional particle-in-cell simulations with Monte Carlo collisions included have revealed formation dynamics of side discharges, suggesting that transverse plasma diffusion and ion induced secondary electron emission play critical roles. Moreover, a novel honeycomb superlattice pattern is observed in experiment, where the side discharges associated with honeycomb superlattice are verified by utilizing a high speed camera. Experimental observations and numerical simulation are in good agreement.
Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is one of the most popular hole transport materials for replacing traditional high-temperature boron diffusion technology due to its low cost and easy preparation. However, pristine PEDOT:PSS has drawbacks, such as poor work function (WF) and poor film quality, which inhibit the improvement of cell efficiency. According to current research reports, a single dopant can improve only one of these two drawbacks. In this paper, we used Nafion to simultaneously improve the WF and wettability of PEDOT:PSS for preparing novel PEDOT:PSS/n-Si hybrid heterojunction solar cells with a tunnel-oxide passivated contact (TOPCon) back surface field structure, which we call PEDOT:PSS-Nafion (PPN)/n-Si hybrid heterojunction TOPCon solar cell. A cell efficiency of 11.08% was achieved after optimizing the ratio of PEDOT:PSS and Nafion. The three easily improved parameters, namely, series resistance (RS), reflectivity, and WF, were studied and optimized through simulation, achieving a cell efficiency of 20.66%. To reduce RS in the experiment, the Triton X-100-doped PEDOT:PSS film (PPTX) was introduced between the n-Si and PPN films to form highly conductive PPN/PPTX double hole transport layers, and the cell efficiency was increased from 11.08 to 13.7%. The experimental and simulated work presented a new thought and practical guidance for realizing low-cost, easy preparation, and high-efficiency silicon-based solar cells.
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