By: Dr. Eng. Agus Purwanto, ST. MT
The conversion of solar energy into electricity becomes main consideration in the few last decades. To convert solar energy toelectricity, a device called solar cell is needed. In the first development, silicon semiconductor was used in the fabrication of solar cell. Recently, a new class of low cost solar cell was developed which is known as dye-sensitized solar cell (DSSC) or Gratzel cell. The fabrication of DSSC needs transparent conducting oxide (TCO) glass for the electrodes. The most extensively used of TCO films are indium doped tin oxide (ITO) and fluorine doped tin oxide (FTO). ITO exhibits better conductivity than FTO, but the lack of indium availibity becomesgreat consideration. For extreme application, FTO shows better performance on the chemical resistance which is good choice for DSSCelectrodes. Unfortunately, these electrodes cost about 40% of the total fabrication cost. Thus, low cost deposition techniques are required to reduce the production cost.
The results of the first year project (2009) showed that the diret deposition on heated glass substrate (pyrosol technique) was promising for the production of high performance FTO film. Using this technique, good FTO film characteristics could be produced. The sheet resistance as low as 12.3 Ω coud be fabricated. The optimal doping concentration was in the range of 8% to 14% mol of NH4F. From XRD characterization, it is found that SnO2 was tetragonal in structure and was highly crystalline. In addition, the FTO film had transparency for above 70% in the range of visible light wavelength. For conclusion, our proposed technique can be used to produce high performance of FTO films which is applicable for the DSSC fabrication.
From the second year project, it was found that the flame assisted spray deposition (FASD) could be used to prepare high performance FTO films. By this technique, an FTO film with a relatively large area was uniformly grown. By varying the NH4F doping concentration, the optimal concentration was established as 8 at.%. XRD spectra confirmed that the as-grown FTO film was tetragonal SnO2. In addition, the FTO film was comprised of nano-sized grains ranging from 40-50 nm. The heat-treated FTO film exhibited a sheet resistance of 21.8Ω. with an avarage transmittance of 81% in the visible region (λ= 400-800 nm). The figures of merit for ΦTC and MTC were 1.1 x 10-2 Ω-1 and 11.5, respectively, which shows that the prepared FTO film can be used for highly efficient dye-sensitized solar cells (DSSCs) electrodes.
During second year project, 1 national publication (conferences), 2 international publications (1 conference and 1 peer-reviewed paper) could be published. Totally, 3 national publications and 2 international publications could be written from this project