In this work, we demonstrate heterojunction photovoltaic devices utilizing transparent and conducting single wall carbon nanotube (SWNT) thin films as the p-layer on n-type crystalline silicon substrate. The best device shows a short circuit current of 2.74 mA/cm2 with an open circuit voltage of 0.4V (AM 1.5). In addition, the concept of applying SWNT film to a thin-film amorphous Si solar cell is also demonstrated. SWNT thin films can be applied via simple solution based methods. SWNT/Si heterojunction devices have remained stable under laboratory conditions for months so far.