Hongzhao Li

Development of a 16.8% Efficient 18-μm Silicon Solar Cell on Steel

Thin crystalline silicon solar cells have the potential to achieve high efficiency due to the potential for increased voltage. Thin silicon wafers are fragile; therefore, means of support must be provided. This paper reports the design, development, and analysis of an 18-μm crystalline silicon solar cell electrically integrated with a steel alloy substrate. This ultrathin silicon is epitaxially grown on porous silicon and then transferred onto the steel substrate. This method allows the independent processing of each surface. The steel substrate enables robust handling and provides a conductive back plane. Three groups of cells with planar and textured structures are compared; significant improvements in Jsc, Voc, and fill factor (FF) are achieved. The best cell shows an efficiency of 16.8% with an open-circuit voltage of 632 mV and a short-circuit current density of 34.5 mA/cm2.

Oxidation Drive-In to Improve Industrial Emitter Performance by POCl3 Diffusion

In this paper, we investigate the influence of different N2/O2 ambient compositions during POCl3 diffusion on the emitter quality, characterized by secondary ion mass spectrometer and electrochemical capacitance-voltage measurements (J0E) and internal quantum efficiency. It is presented that O2 concentration during the drive-in step strongly impacts both emitter electrical properties and cell performances, supported by the loss breakdown analysis. This process can be easily adapted to the industry, improving the emitter quality for screen-printed solar cells.

Empirical and Quokka simulated evidence for enhanced V OC due to limited junction area for high efficiency silicon solar cells

A new design for high efficiency silicon solar cells with the use of limited p-n junction area and point Al rear contact is proposed. In this work, planar test devices with different emitter area and spacing are fabricated to demonstrate the limited junction area (LIA) design can improve VOC for a well-designed cell structure. Interim lifetime and PL measurements during fabrication confirm lower dark saturation current (I0) and higher implied VOC (iVOC) in the LIA samples with a robust surface passivation scheme. Higher VOC and efficiency are also simulated with Quokka on some LIA devices compared to the full area emitter control sample.

Improvement of industrial phosphorus diffused emitters and impact on solar cell efficiencies

In this study, we investigate the importance of the minority carrier lifetime (τp0) and surface recombination velocity (SRV) of industrial n-type emitters in improving emitter performance and improving solar cell efficiency. When emitters with higher τp0 values are applied to Al-BSF and PERC solar cells separately, they show slightly different responses to the increase in τp0. Simulation results indicate that PERC solar cells receive a larger efficiency enhancement with the same increase in τp0 than that for Al-BSF cells. This is due to the fact that emitter recombination can be a major contributor to efficiency loss for solar cell structures like PERC where the rear surface is well passivated by dielectric stacks. Additionally, LDSE cells have a stronger dependence on the surface passivation quality, especially for the PERC structure.