Key Word: CuPc thin film, ITO glass substrate, organic film
Harjana dan Ari Handono Ramelan
LPPM UNS, DP2M Dikti, Penelitian, Hibah Strategi Nasional, 2009
These days, the solar-power conversion efficiency of a monocrystalline silicon solar cell has reached 24 %. However, production of this kind of inorganic device requires difficult manufacturing processes involving high temperatures as well as numerous lithographic steps. Thus, an alternative way of producing a photovoltaic cell is needed, which is less expensive and more economic. One alternative way is to use organic photovoltaic cells, because chemical synthesis can easily modify a molecular structure to achieve a desired optical or electrical property. Most of the small molecules used in organic photovoltaic cells are deposited by using thermal evaporation to obtain a desired film thickness. These photovoltaic cells have been intensively studied for the last ten years. In 1986, Tang developed a photovoltaic cell by using CuPc/PV organic materials and obtained a solar power efficiency of about 1 % with corresponding external quantum efficiency of about 30 %. It is reported that reported a photovoltaic cell having a power-conversion efficiency of 3.6 % in a structure of ITO/CuPc/C60/BCP/Al under illumination of AM 1.5 solar spectrum. Conjugated polymers can also be used for photovoltaic devices by spreading a solution on a substrate by means of spin coating. Polymers make it possible to manufacture large-area, flexible and lightweight devices. Polymer photovoltaic cells with a heterojunction structure show an estimated power-conversion efficiency of 2 % under illumination of AM 1.5 solar spectrum. Optical illumination onto an organic semiconductor generates electron-hole pairs that are called excitons, with a binding energy higher than that in inorganic semiconductors. To transport generated carriers to the opposite electrodes, an electric field should be applied to separate the excitons. Since the exciton diffusion length in organic semiconductors is about 10 nm, the photoactive layer thickness is important in the aspect of efficiency of the device.8 In this paper, we report the deposition condition effects in optical properties and crystal structure of CuPc organic film. The growth of CuPc thin film on a ITO glass substrate has been done using vacuum evaporation method. The deposition of CuPc thin film has done by varying of CuPc mass from 50 mg to 200 mg. The characterization of CuPc film was conducted by using UV-Visible Spectrophotometer (UV-Vis) for optical properties of CuPc thin film including absorbance, transmittance, energy gap. The thickness of the CuPc film was determined from absorbance value. The crystal structure was determined by using X-Ray Diffractometer (XRD). UV-Vis results show that the absorbance and transmittance of thin film depend on thickness of the thin film. The energy gap of the thin film is approximately 1.6 eV. The CuPc thin film has a crystal structure of (100), ( 13), ( 13), (112), (311), ( 06), (212) planes