Analysis of Back Surface Field (BSF) Performance in P-Type And N-Type Monocrystalline Silicon Wafer

Ferdiansjah Ferdiansjah,Faridah Faridah,Kelvian Tirtakusuma Mularso,Ir Sunarno,Agus Pulung Sasmito,Liem Peng Hong

doi:10.1051/e3sconf/20184301006

Abstract

Back Surface Field (BSF) has been used as one of means to enhance solar cell performance by reducing surface recombination velocity (SRV). One of methods to produce BSF is by introducing highly doped layer on rear surface of the wafer. Depending on the type of the dopant in wafer, the BSF layer could be either p+ or n+. This research aims to compare the performance of BSF layer both in p-type and n-type wafer in order to understand the effect of BSF on both wafer types. Monociystalline silicon wafer with thickness of 300 μm. area of 1 cm2, bulk doping level NB = 1.5×1016/cm3 both for p-type wafer and n-type wafer are used. Both wafer then converted into solar cell by adding emitter layer with concentration NE =7.5×1018/cm3 both for p-type wafer and n-type wafer. Doping profile that is used for emitter layer is following complementary error function (erfc) distribution profile. BSF concentration is varied from 1×1017/cm3 to 1×1020/cm3 for each of the cell. Solar cell performance is tested under standard condition, with AM1.5G spectrum at 1000 W/m2. Its output is measured based on its open circuit voltage (Voc). short circuit current density (JSC), efficiency (η). and fill factor (FF). The result shows that the value of VOC is relatively constant along the range of BSF concentration, which is 0.694 V – 0.702 V. The same pattern is also observed in FF value which is between 0.828 – 0.831. On the other hand, value of JSC and efficiency will drop against the increase of BSF concentration. Highest JSC which is 0.033 A/cm2 and highest efficiency which is 18.6% is achieved when BSF concentration is slightly higher than bulk doping level. The best efficiency can be produced when BSF concentration is around 1×1017cm-3.. This result confirms that surface recombination velocity has been reduced due to the increase in cell’s short circuit current density and its efficiency. In general both p-type and n-type wafer will produce higher efficiency when BSF is applied. However, the increase is larger in p-type wafer than in n-type wafer. Better performance for solar cell is achieved when BSF concentration is slightly higher that bulk doping level because at very high BSF concentration the cell’s efficiency will be decreased.

Highlights

Solar cell has grown thinner in past decade due to the desire to reduce material cost
Current solar cell that widely produced has P-type based monocrystalline wafer and it shows an increase in its effciency
This layer will function as internal electric field generator that will repel photogenerated minority carrier near the rear surface, and will reduce back surface recombination velocity

Summary

Introduction

Solar cell has grown thinner in past decade due to the desire to reduce material cost. When the wafer become thinner, effect such as surface recombination will become dominant, a way to limit or reduce this effect should be applied. One the method to limit backsurface recombination in a P-type wafer is by applying aluminium layer upon the rear surface of the cell. This layer will function as internal electric field generator that will repel photogenerated minority carrier near the rear surface, and will reduce back surface recombination velocity. The effectiveness of aluminium layer as back surface field generator will depend on Al concentration. This concentration will be limited to its maximum solid solubility in Si, which is around 1018 cm-3 at the standard firing temperature of around 750oC [1]

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