Characterization of PVA/CuI polymer composites as electron donor for photovoltaic application

Nanopolymer composite of PVA/CuI has been prepared as in both colloidal forms and solid layers and characterized their structure by X-ray diffraction, scanning electron microscopy, AC spectroscopy and optical absorption in UV–visible. It is observed that with the growth of CuI nanoparticles (in the range of 26–46 nm in size) reduces the PVA polymer crystallinity. The temperature dependence of bulk conductivity for PVA/CuI nanocomposite illustrated that the composites behave as the semiconducting materials with the activation energy in the range of 0.27–1.02 eV. It was observed that the direct optical band gap reduces from 3.53 eV to 1.7 eV as the concentration of CuI nanoparticles in the PVA increased from 0% to 10%. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of the PVA/CuI nanocomposites were estimated from the cyclic voltammetry. The electrochemical band gap, that is, the difference between HOMO and LUMO levels also decreases with the increase in the concentration of the CuI in PVA, which is in agreement with the trend observed in the optical band gap. The current–voltage characteristics of the devices based on PVA/CuI nanocomposites, in dark shows that these composites behave as p-type semiconductors. We have also investigated the J–V characteristics under illumination and found that the power conversion efficiency is very low but these composites can be used as electron donor for bulk heterojunction solar cells along with fullerene derivatives as electron acceptor.