Japanese researchers have produced an HJT solar cell with silicon and a polymer material known as PEDOT:PSS at room temperature. It has an efficiency of 10.1%, an open circuit voltage of 0.57 V, a short-circuit current density of 33.3 mA/cm2 and a duty factor of 0.53.
To form the electrodes without using expensive processes such as screen printing, chemical coating, and vacuum evaporation, the researchers used a highly conductive silver (Ag) ink to coat the semiconductor materials as electrodes. Thus, the fabrication process of their solar cells involved only three coating processes: coating a PEDOT:PESS layer on a bare Si wafer, a top Ag electrode on the PEDOT:PSS layer, and a bottom Ag electrode on the back surface of Si. wafer.
The researchers then investigate the optimal process conditions and sequence that maximizes the solar cell’s performance. They found the best results for cells made by first using a wet hydrofluoric acid treatment to remove the original oxide layer from the Si surface, then a coating behind the Si wafer, followed by immersing the Si wafer in deionized water, and then applying a PEDOT coating. :PSS layer and finally coating the top of the wafer.
After this process, the team said they found “a drastic change in cell efficiency during the immersion time (of the wafer in deionized water), where too little or too much oxidation of the Si top surface seriously degrades the cell.” The researchers found that the optimal time for this process is one minute and the ideal spin speed for the PEDOT:PSS spin coating is 5,000 rpm.
Laboratory measurement 8 mm2 produced under these conditions had a conversion efficiency of 10.1%, an open circuit voltage of 0.57 V and a short circuit current density of 33.3 mA/cm2and a fill factor of 0.53.
The academics said the efficiency value is far from state-of-the-art PEDOT:PSS/Si HJT solar cells “due to the severe limitation of the process conditions… The low fill factor that severely limits the efficiency is due to the relatively high series resistance.”
Nevertheless, the researchers noted that their fabrication method “may lead to convenient, low-cost, and efficient fabrication of photovoltaic devices, which is particularly useful for use in developing countries and educational settings.”
They shared their findings in the paper, “All-Environment, Room-Temperature Processed Solar Cell from Bare Silicon Wafer,” published recently PNAS Nexus.