A crystalline Si solar cell using a carbon nanotube thin film as the back electrode

Due to their outstanding charge collecting and transport ability, carbon nanotubes (CNTs) can be used as electrode materials in solar cells. Here, we replaced the aluminum back electrode in a crystalline silicon (c-Si) solar cell with a CNT thin film to form a c-Si/CNT film solar cell. The c-Si/CNT solar cell had a high short-circuit current density of 35.5 mA cm^-2, which is higher than that using aluminum as the back electrode, indicating that CNTs can be used as hole transport materials in silicon-based solar cells. The power conversion efficiency of the c-Si/CNT solar cell was increased from 7.1% to 10.9% by dropping a few drops of a dilute HF solution (5 wt%) at the interface of the c-Si and the CNT film. This is because HF etches away the oxide layer on the c-Si surface, increases the interfacial contact area between the CNT film and the c-Si and decreases the recombination rate of electron/hole pairs.