Investigating the Humidity Effect on SiNS/PEDOT: PSS Hybrid Solar Cell and Power Conversion Efficiency Recovery by Re-Deposition of the Hole Transporting Layer

The degradation of silicon nanostructure / poly(3,4-ethylenedioxylthiophene : poly(styrenesulphonic acid) (SiNS/ PEDOT:PSS) hybrid solar cell due to the moisture is investigated with an environmental chamber. The unencapsulated devices were tested under different relative humidity (RH) varied from (15% to 100%). Under different RH, the devices show various degradation trends. After 3hrs of storage under 100% RH, the average device power conversion efficiency (PCE) drops from 6.52% to 1.27%. While the device is stored under 15% RH, the averaged PCE just drop from 6.40% to 5.49% and the device at 60% RH degrades from 5.97% to 3.12%. To understand the cause of the device degradation, we compare the ITO conductivity and apply tunneling electron microscopy (TEM) to study the growth of the silicon dioxide layer on the silicon nanostructures. We confirmed that the major cause of the PCE drop in the current devices are due to the decrease of the PEDOT:PSS conductivity and the increase of the interface resistances. By re-depositing the PEDOT:PSS layer onto the degraded device and recycling the Si (and fresh ITO), we demonstrated that the efficiency of the device can be partially recovered (to fully recovered). The current work not only highlighted the importance of the humidity control in these SiNS/PEDOT:PSS hybrid solar cells, but also identified the major causes of the device degradation. The observation has been reconfirmed by recovering the PCE of the degraded device with a fresh PEDOT:PSS layer and a fresh ITO.