Effect of nanowire lengths on polymer-Si nanowire hybrid solar cells

We demonstrate Al/Si NWs/poly(3,4-ethylenedioxy thiophene)/poly(styrenesulfonate)(PEDOT:PSS)/ITO hybrid solar cells. The lengths of these n-type Si NWs could be controlled by the etching time from 15min to 40min in an aqueous solution of AgNO3 and HF acid for this demonstration. The conductive polymer, PEDOT:PSS, was spin-coated on ITO glass. Before the PEDOT:PSS thin film dried, the top portion of the Si NWs were immersed in the wet PEDOT:PSS thin film. Current versus voltage measurements which were performed under broad band light irradiation show that Si NWs/PEDOT:PSS heterojunctions have remarkable photosensitive behavior. Moreover, when the nanowire etching time is raised, the probability of collecting photogenerated carriers at the interface after separation of hole-electron pair increases because of increasing interface area in the radial directions between the PEDOT:PSS and the silicon nanowire array, which palys an important role in collecting photogenerated electrons and acts as a conducting path to the aluminum electrode, resulting in raising fill factors and power conversion efficiencies.