Analysis of photoconductivity and effects of CuI as a templating layer in fullerene based Schottky solar cells

Abstract

In this thesis, the bulk-ionized photoconductivity of fullerenes in the Schottky solar cells has been investigated by three experiments. First, comparison of C60 and C70 is carried out. Since C70 has larger exciton generation rate (more overlap with solar spectrum about 2.3 times) than C60, photoconductivity of C70 is higher than C60. But, increase in photoconductivity is only 1.7 times, due to difference in thermalization distance. It is discussed with X-ray scattering data. Then, work function of electrode is changed with interfacial layers. Linear dependence of photocurrent on electric field is observed and changing the interfacial layer to modify work functions of electrode leads to variation of the built-in potential (Vbi). These have been confirmed by calculations using equation from photoconductivity and capacitance-voltage (C-V) characteristics. Third experiment is inserting CuI as a templating layer. In the images of grazing incidence wide angle x-ray scattering (GIWAXS), C60 on CuI layer shows higher crystallinity than C60 on ITO substrate. The preferred orientation is FCC(111) which is closed packing plane for vertical direction to substrate. This effect makes photoconductivity increase by 43.8% in MoO3 used and by 93.5% in ReO3 used Schottky solar cells. Finally, based on these results, high efficiency solar cells with 6.2% have been achieved.