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The investigation on the quality of aluminum rear emitter for n-type solar cells

Since rear emitter characterization is the crucial factor for aluminum back junction n-type cells, the emphasis of this paper is focused on the quality of this Al-Si alloy layer. Diffusion profile test is used to describe the diffusion of Al in the silicon rear side. It is found that the Al-Si alloy layers thickness of about 6 μm should be better. In order to get a thicker thickness, a higher temperature or a slow belt velocity is needed in the firing process. However, it is found that a higher temperature is not suitable, which will cause a higher concentration of Al atoms in the layer. A lower firing speed almost only thickens the alloy layer. A high Voc of 650 mV and a high fill factor of 0.818 have been obtained by slowing down the firing speed.

The investigation on the front surface oxidation for aluminum rear emitter n-type solar cells

Since front surface field characterization is one of the crucial factors for aluminum back junction n-type cells, the emphasis of this paper is focused on the quality of this n+ layer. Oxidation process is wildly used for high efficiency solar cells. Higher temperature and thicker SiOx layers can provide a better passivation effect. However oxidation process can also reduce the surface concentration of phosphorus, and thicken the n+ layer. Both of a too low surface concentration and a thick n+ layer are not needed. After the optimization, the oxidation temperature and time are fixed on 900 □ and 15 min, respectively. The passivation effect is well-done; the minority lifetime of the wafers after oxidation is nearly 400 μs. And the sheet resistance of about 150 Ω/□ is better for the cells fabrication. A high open-circuit voltage of over 645 mV and a high fill factor of over 0.80 have been obtained.

The investigation on the texture differences between p-type and n-type crystalline silicon wafers

Surface reflectivity is one of the important factors for solar cells. The anisotropic etching behavior of different types of monocrystalline silicon was studied in this paper. The etching rate is determined as a function of temperature, crystal orientation, and etchant composition. It is found that the etching rate of n-type silicon is faster than that of p-type silicon in the same corrosive solution. The reason is analyzed in this paper. For p-type silicon wafers, well-proportioned texturization was obtained in 2.0% NaOH(in mass, the same below) and 10% IPA aqueous solution at 80□ with 25 min, while for n-type wafers, the process time should be reduced to 20 min. The texturization was better when adding 3% Na2SiO3 in the solution, and the lowest reflectivity could be 9.5%.

Effect of post-annealing treatment on the contact resistance of small molecule solar cells

Small molecule solar cells with structure of ITO/ZnPc/C60/LiF/Al were fabricated by vacuum evaporation method, and thermal annealing treatment was considered to be an effective and economized approach to further improve the power conversion efficiency and lifetime of devices. The optimal annealing process was 100°C, 20min in air ambient, and it respectively promoted the power conversion efficiency by 2.4 times and the stability of unencapsulated devices by 4.4 times As a conclusion, the main reason is attributed to the decrease of contact resistance. Moreover, the improvement of interfacial morphology at the ITO/ZnPc interface contributes the benefit.

The investigation on fast and uniform diffusion for silicon solar cell production

Diffusion tubes are used in normal production process. It can provide a high minority carrier lifetime. But it is determined by the cleanliness of the tubes. Trace amount of impurity in the tubes will strongly influence the lifetime. Additionally, the phosphorous source, POCl3 is a highly toxic and corrosive chemical, which needs a high cost to manage. In this paper, a fast and uniform diffusion process used for solar cell production is investigated. A kind of nontoxic and low corrosive phosphorous source is sprayed on the surface of silicon wafers. And then the wafers are transported inline into a high temperature nitrogen atmosphere by an alloy belt. After this inline diffusion, the unevenness of sheet resistance can be decreased to below 5%, the efficiency of the cells using inline diffusion is a little higher than that of the cells diffused in tubes which may be attribute to the excellent uniformity.

The investigation and optimization of LiF cathode buffer layer based on ZnPc/C 60 solar cells

Using electrode buffer layer is one of effective ways to enhance electric performances of organic solar cells. And LiF is the widest materials, which is used as a cathode buffer layer. In this paper, small molecule organic solar cells based on ZnPc and C60 are fabricated. And the LiF cathode buffer layer is studied. The mechanisms and functions of LiF layer are summarized and qualitatively explained. The thickness of LiF is also investigated. And it is found that its optimum thickness must be controlled at the interval from 1.0nm to 1.5nm.

Optimization of the structure of bilayer organic solar cells based on light intensity distribution and quantity of effective excitons

The light intensity distribution inside organic solar cells is described by optical propagation matrix and the quantity of effective excitons is defined in this paper. The quantity of effective excitons describes the total intensity near the donor/acceptor interface, which can contribute to the generation of holes and electrons. The optimum structure then can be obtained by maximizing this parameter. In this paper, CuPc/C60 structure is taken as an example. It is found the optimum structure is CuPc(15nm)/C60(40nm). The verification experiments are established and only 5nm error appears in the thickness of CuPc.