M.Phil Thesis, Department of Physics, University of Ruhuna (2006)

Supervisors: C. A. N. Fernando ( nandanaf@phy.ruh.ac.lk)

Investigation of crystal violet dye sensitized CuSCN/n-Cu2O junction photo electrode in solar energy conversion devices
T. N. Gamage

A stable solid state photovoltaic cell is presented by sandwiching crystal violet dye between n-Cu2O prepared on a copper substrate and p-CuSCN transparent thin film prepared on n-Cu2O considerably improving a previously presented (82) solid state photovoltaic cell made from bare p-CuSCN. After sandwiching crystal violet dye between n-Cu2O and p-CuSCN a photo current enhancement can be observed clearly compared to the solid state photovoltaic cells made with bare n-Cu2O, n-Cu2O/p-CuSCN and dye deposited p-CuSCN. This photocurrent enhancement with connection to the dye sensitized junction photoelectrode is due to the efficient charge separation process provided at the space charge layer. The variation of photocurrent quantum efficiency (%) obtained due to the dye sensitization with dye concentration (D0) of the devise is presented. A relationship  = AD0 – BD02 is found by solving the rate equations related to the dye sensitization. Parameters A and B are obtained relating to the rate constants and various factors which can be influenced to . Demonstrating various experimental results, kinetics of the photocurrent generation in the solid state photovoltaic cell is discussed.

A photoelectrochemical cell is made by sandwiching a dye between p-CuSCN and n-Cu2O semiconductor films. A photo current enhancement is clearly found for the dye sensitized junction photoelectrode n-Cu2O/Dye/p-CuSCN in comparison to that of the systems p-CuSCN/Dye, n-Cu2O/p-CuSCN or n-Cu2O bare photoelectrochemical cells. Well cleaned copper substrates are boiled 15 minutes in a 10-4M CuSO4 solution to fabricate n-Cu2O films to prepare Cu/n-Cu2O photoelectrodes. Cu/n-Cu2O films are immersed in a p-CuSCN preparation solution to fabricate transparent p-CuSCN thin films, to prepare Cu/n-Cu2O/p-CuSCN junction photoelectrode. There after, Cu/n-Cu2O/p-CuSCN films are immersed in a 10-3M Crystel Violet Dye Solution for severel minutes to prepare Cu/n-Cu2O/Dyep- CuSCN photoelectrodes, XRD data reveal that the formation of n-Cu2O and p-CuSCN, thin films in the Cu/n-Cu2O/p-CuSCN junction photoelectrode. The reason for the photocurrent enhancementin the Cu/n-Cu2O/Dye/p-CuSCN is the efficient charge separation provided at n-Cu2O/p-CuSCN, junction for the photogenerated carries created by the dye sensitization process associated with p-CuSCN transparent thin film and the direct light absorption of the n-Cu2O film. A dye sensitization process between the dye and the n-Cu2O films is not observed. 10-4 M Fe2+/Fe3+ redox couple is used as the electrolyte.