Optimization of Monocrystalline Silicon Solar Cells Based on the Phosphorus Diffusion Time
Paper ID : 1172-ICRSSSA
Authors
Rabaa Mahmoud Ali *1, Mohamed Zahran2, Mai Allam3, Aref Eliwa4, Amr Bayoumi5
1المعمل القومی المصری الصینى للطاقة الجدیدة والمتجددة بسوهاج
2National Authority of Remote Sensing and Space Science “NARSS”, Cairo, Egypt
3National Research Center Academy of Scientific Research and Technology, Cairo, Egypt
4Photovoltaic Cells Department, Electronics Research Institute, Cairo, Egypt Electrical Engineering Department, Faculty of Engineering, 6 October University, Egypt
5Electrical Engineering Department, Faculty of Engineering, Zewail University, Egypt
Abstract
Optimization of diffusion profile is required to obtain junction depth and diffusion layer sheet resistance that are suitable for P-N junction that effectively separating photogenerated electrons and holes to improve efficiency.
POCl3 diffusion technique used to deposit N-layer on P-type substrate. P-type wafers of 156×156 mm2 and 180 µm thickness, doped with boron with resistivity of 0.828 Ω.cm. To evaluate influence of diffusion time on sheet resistance and electrical parameters of monocrystalline Si SC, time varied from 600 sec to 1800 sec at constant temperature of 825 ℃ for pre-deposition and 875 ℃ for drive-in and gases flow rate (POCl3/O2) of 1900/2800 SCCM/min for Pre-deposition and 1200/2000 SCCM/min for drive-in. Sentaurus TCAD used to simulate diffusion process to know diffusion time effect on physical structure of emitter as phosphorous doping profile and junction depth.
Results show that sheet resistance decreases while diffusion time increases where it decreased from 33 Ω/□ at 600 sec to 25 Ω/□ at 1000 sec. However, at 1300 sec, sheet resistance started to increase again.
The highest efficiency is 18.18% at sheet resistance of 25Ω/□ and 1000 sec.
As deposition time increases, heavily doped emitter will be formed leading to low sheet resistance resulting in reducing low contact resistance. But with very long deposition time, phosphorus accumulates at cell surface. The excess phosphorus atoms create a defect source that makes emitter electrically inactive. This dead layer is the major recombination source of photogenerated carriers.
So, diffusion time should be appropriate not too long or too short
Keywords
Monocrystalline silicon solar cell; POCl3 diffusion technique; Diffusion time; Sentaurus TCAD simulation program; Sheet resistance; junction depth; Diffusion profile; Electrical parameters of Si SC; Efficiency.
Status: Accepted (Oral Presentation)