This paper presents a comprehensive analysis of the characteristics of the crystalline silicon solar cell that depend on the etched-back structure of the selective emitter by TCAD simulation. The simulation results show that a solar cell with an etched-back selective emitter can have much improved cell characteristics compared to those of the a solar cell with a homogenous emitter by increasing short wavelength spectral response characteristics by decreasing its recombination rate and defect density in the lightly doped region. With the optimized heavily/lightly doped emitter region, the short circuit current (J SC , the open circuit voltage (V OC , the fill factor, and the conversion efficiency of the crystalline silicon solar cell with an etched-back selective emitter were 35.88 mA/cm 2 , 638.8 mV, 78.85%, and 18.07% with 60 nm emitter etched-back depth, respectively. The etched-back structure of the selective emitter increased the short circuit current by 1.2 mA/cm 2 and conversion efficiency by 0.6% from those of the solar cell with a homogeneous-structure emitter, respectively. Therefore, the carrier concentration gradient in the selective emitter can be an important factor in the effective collection of minority carriers.
The low level doping of a selective emitter by etch back is an easy and low cost process to obtain a better blue response from a solar cell. This work suggests that the contact resistance of the selective emitter can be controlled by wet etching with the commercial acid barrier paste that is commonly applied in screen printing. Wet etching conditions such as acid barrier curing time, etchant concentration, and etching time have been optimized for the process, which is controllable as well as fast. The acid barrier formed by screen printing was etched with HF and HNO3 (1:200) solution for 15 s, resulting in high sheet contact resistance of 90 Ω/sq. Doping concentrations of the electrode contact portion were 2 × 1021 cm−3 in the low sheet resistance (Rs) region and 7 × 1019 cm−3 in the high Rs region. Solar cells of 12.5 × 12.5 cm2 in dimensions with a wet etch back selective emitter Jsc of 37 mAcm−2, open circuit voltage (Voc) of 638.3 mV and efficiency of 18.13% were fabricated. The result showed an improvement of about 13 mV on Voc compared to those of the reference solar cell fabricated with the reactive-ion etching back selective emitter and with Jsc of 36.90 mAcm−2, Voc of 625.7 mV, and efficiency of 17.60%.
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