Effects of organic self-assembled polymer and metal phthalocyanine multilayers on the surface photovoltaic properties of indium tin oxide and titanium oxide

Using a layer-by-layer self-assembly technique, we have deposited multilayers of nickel phthalocyanine tetrasulfonate (NiPc) and poly(diallyldimethylammonium chloride) (PDDA) onto indium tin oxide (ITO) and ITO/TiO₂ substrates, respectively. To probe charge-transfer properties of these self-assembled multilayers on conductive and semiconductive surfaces, Kelvin probe and surface photovoltage measurements have been carried out. The results showed an oscillating behavior of the surface potential or work function (ΔΦ) as the surface layer was alternated between PDDA and NiPc on both substrates with or without light. The average width of this surface potential oscillation was around 350 mV. These changes in surface potential, induced by self-assembled PDDA or NiPc, were due to the modulation of electron affinity rather than band bending at ITO surfaces. The photoinduced change in band bending (δΔV) however, has little correlation to the number of layers (PDDA or NiPc).