ZnO Thin Films with adjusted Surface Work Function for Organic Solar Cells

An ITO PEDOT PSS poly 3,4 ethylendioxythiophene poly styrenesulfonate electrode is widely used as anode in organic solar cells OSCs . Aluminium doped zinc oxide ZnO Al is presented as a possible substitution for ITO in such anodes. Containing only abundant elements, ZnO Al serves as cost effective alternative to the indium requiring ITO. To optimize the surface work function of the ZnO Al PEDOT PSS anode the pH value of the PEDOT PSS dispersion is modified. In this work 2 dimethylaminoethanol DMAE is used for the pH modification of the PEDOT PSS dispersion. PEDOT PSS dispersions modified by different DMAE concentrations were applied to both ITO and ZnO Al films. The surface work functions of the prepared electrode stacks were determined by ultraviolet photoelectron spectroscopy UPS and compared to the corresponding pH value. Additionally, we investigated the influence of the modified PEDOT PSS layers on the photovoltaic properties in ZnPc C60 based organic solar cells using ITO as well as ZnO Al as TCO. By analysis of the solar cell performance of ZnO Al based devices we identified a range of the DMAE concentrations showing the highest device efficiency. In this range we observed a solar cell performance similar to that of solar cells with ITO as TCO. Comparison of the open circuit voltage and the surface work function shows that a minimum work function of amp; 934; 4.7 eV is necessary to form a charge selective contact at the anode absorber interfac