Abstract
In this paper, the relationship between coordination complexes and electrical properties according to the bonding structure of boron and silicon was analyzed to optimize the p–n junction quality for high-efficiency n-type crystalline solar cells. The p+ emitter layer was formed using boron tribromide (BBr3). The etch-back process was carried out with HF-HNO3-CH3COOH solution to vary the sheet resistance (Rsheet). The correlation between boron–silicon bonding in coordination complexes and electrical properties according to the Rsheet was analyzed. Changes in the boron coordination complex and boron–oxygen (B–O) bonding in the p+ diffused layer were measured through X-ray photoelectron spectroscopy (XPS). The correlation between electrical properties, such as minority carrier lifetime (τeff), implied open-circuit voltage (iVoc) and saturation current density (J0), according to the change in element bonding, was analyzed. For the interstitial defect, the boron ratio was over 1.8 and the iVoc exceeded 660 mV. Additional gains of 670 and 680 mV were obtained for the passivation layer AlOx/SiNx stack and SiO2/SiNx stack, respectively. The blue response of the optimized p+ was analyzed through spectral response measurements. The optimized solar cell parameters were incorporated into the TCAD tool, and the loss analysis was studied by varying the key parameters to improve the conversion efficiency over 23%.
Highlights
The n-type crystalline silicon solar cells possess advantages in terms of high efficiency due to their higher minority carrier lifetime, robustness and light-induced degradation (LID) in comparison with p-type substrates silicon solar cells [1]
Optimization of diffusion technology to form good-quality p–n junctions is the basis for realizing the high-efficiency potential of n-types and must be emphasized in the future. This is because the formation of p+ diffused layers using BBr3 is expected to maintain about 85% of the market share until
It can be interpreted that as the binding energy shifts, the interstitial defect decreases, and the sufficiently activated boron in silicon increases. It shows an increase in conductivity [19], which affects the electrical properties of the p+ diffused emitter and the output properties of the solar cell
Summary
The n-type crystalline silicon solar cells possess advantages in terms of high efficiency due to their higher minority carrier lifetime, robustness and light-induced degradation (LID) in comparison with p-type substrates silicon solar cells [1]. P-type-based solar cells dominate the photovoltaic market with the advantage of material cost due to their cheaper wafer cost and process compatibility and the fact that they have an formed emitter and local back-surface field (LBSF) using phosphorus diffusion and Al–Si-alloy formation through laser-opening screen printing—a fast-firing process [2] Despite this situation, the International Technology Roadmap for Photovoltaic (ITRPV) predicts that n-type products, which currently have about 10% market share, will have an equal market share with p-type products by 2029 [3]. The mass production of various n-type high-efficiency technologies, such as the TOPCon ( known as passivated contact) and the monopoly solar cell [4], which is under continuous development, will accelerate this situation [5,6,7,8] In this regard, optimization of diffusion technology to form good-quality p–n junctions is the basis for realizing the high-efficiency potential of n-types and must be emphasized in the future. Assuming that the sheet resistance (Rsheet ) is higher than the current as predicted in the market, determination of the dominant factor for improving the efficiency and loss factor in whole solar cell structures, such as recombination front/rear surfaces and contact loss, was analyzed using the TCAD tool [12,13]
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