Publication

Abstract :

The important aspect of PEC solar cells (solid-liquid interface) with other conventional cells (solid-solid interface) are, it contains two interfaces and the charge transport takes place from electronic to ionic and vice versa. In the case of PEC solar cells both energy conversion and energy storage is possible and it is not sensitive to the defects in semiconductor and is easy to form solid/liquid junction. In the present study CdSe (II-VI semiconductors) is used as photo electrode in PEC solar cells and they are prepared by electron beam evaporation technique at a pressure of 10-5 Torr and at different substrate temperature (Ts-27,100 and 200?C). The thickness of the film is ~180nm. The X-ray diffraction analysis shows the preferred orientation of the crystals along (002) direction. The grain size was found to be in the range of 25-39nm. It is noted that the grain size of the films prepared at RT is 25nm and when the temperature is raised to 100?C, the grain size increased to 39nm. This may be attributed to the fact that at low temperature, the ad atoms have low mobility and it is difficult to form isolated small islands and when the Ts increases the mobility increases and hence favors the grouping and nucleation which leads to increase in grain size. Again when the temperature increases (200?C) the desorption of ad atoms which is due to greater absorption of energy than the surface energy takes place and the size decreases to 26nm.The other structural parameters such as strain, dislocation density and the number of crystallites/m2 also varies accordingly.The optical constants are calculated using the transmission graph (300-1500nm). A shift in the optical absorption edge at lower wavelength is observed and it may be due to the increase in grain size which leads to reduction in the density of grain boundary trapping centers (2.29eV-2.18eV). When the temperature increases (200?C), the transmission decreases which may be due to scattering of light at the grain boundaries and hence the band gap increases (2.456eV). For the PEC studies, the thickness of CdSe films was kept as 400 nm. The out-put characteristics of PEC solar cells are studied with the configuration of CdSe (area exposed 0.5x0.5cm)/1M NaOH-1M Na2S-1M S]/graphite. The PEC cells were illuminated at 100 mW/cm2 and the I-V curves were plotted by observing the current and voltage simultaneously by varying resistance. The cell parameters are found to increase first upto 100oC and then decreased. The maximum values obtained for the CdSe films deposited at 100 oC are: open circuit voltage Voc = 0.422 V, short circuit current Isc = 14.5 mA/cm2, Fill Factor FF = 0.64, efficiency η % = 5.60. The increasing trends for the CdSe films deposited at 100 oC may be attributed to the nanocrystalline nature and the resistivity of these films, which might have been optimum when compared to other CdSe films prepared at different Ts.