Fabrication and characterization of monocrystalline silicon solar cell

Abstract

In the present study, monocrystalline silicon solar cells are fabricated using variation of texturing time and chemicals like Potassium Hydroxide (KOH) and Isopropyl Alcohol (IPA). Fabricated solar cells are then characterized using different characterization techniques. During the fabrication of solar cell, a number of process steps are followed. At first, p-type square silicon wafers of 127×127 mm2, 200 μm in thickness and (100) oriented Czochralski Si (or Cz-Si) are taken. In this research, 14 sample wafers are taken for the cleaning and texturing. The samples are cleaned and textured using a chemical solution of KOH, IPA and H2O (De-ionized) at 70° C temperature by the variation of time, KOH and IPA. Then the morphology of the samples is studied using the Field Emission Scanning Electron Microscope (FESEM) and the surface reflectance is measured by the Surface Reflection Measurement (SRM) system. From the SEM morphology and SRM result, it is observed that the sample textured with 10 minutes time gives more uniform pyramid structure and minimum surface reflectance of about 15.08 %. Sample textured with KOH concentration of 1 gram gives more uniform pyramid structure and minimum surface reflectance of about 15.08 % and the sample textured with IPA concentration of 7 ml gives more uniform pyramid structure and the lowest surface reflectance of about 13.59 %. It is also observed that sample textured with 10 minutes time is found the best for solar cell fabrication and named in respect of surface morphology as SC-A and sample textured with the chemical variation like KOH and IPA using the chemical recipe of KOH: IPA: H2O (DI) = 1 gram: 7 ml: 25 ml for etching time 10 minutes at 70° C temperature is found the best for solar cell fabrication and named as SC-B. Fabrication of solar cell, SC-A and SC-B is successfully completed by following the same process steps like edge isolation of the wafers by the diffusion barrier past for masking the edge of the wafers, phosphorous diffusion by the high temperature diffusion furnace to form n-type layer on the p-type wafer, sheet resistance measurement using the four point probe method before and after the phosphorous diffusion to check phosphorous is properly and uniformly doped or not, metallization by screen printers to collect electricity from the solar cell and finally rapid thermal annealing is performed to form ohmic contacts between metal and semiconductor. Fabricated monocrystalline silicon solar cells are then characterized using three different characterization techniques. Transmission Line Method (TLM) is used to measure the contact resistance between metal and semiconductor of a solar cell. From the TLM results, it is found that front and back contact resistance for SC-A is 0.414 Ω and 1.10875 Ω respectively and for SC-B is almost same as SC-A due to the same doping concentration and metallization materials. Surface Photovoltage (SPV) measurement system is used to determine the minority carrier diffusion length and life time. From the SPV results, it is found that minority carrier diffusion length and life time for SC-A are 82.31 μm and 2.51 μsec respectively and for SC-B are 86.41 μm and 2.75 μsec respectively. Light-Current-Voltage (LIV) measurement system is used to measure the efficiency of a solar cell. From the LIV results, it is found that the efficiency for SC-A and SC-B is 6.89 % and 7.69 % respectively. From the comparison, it is found that the efficiency of solar cell, SC-B is higher than the solar cell, SC-A. The efficiency for both the samples found in the present study is much higher than the efficiency found the solar cells fabricated in the solar lab previously.