Differential Pulse Electrodeposition of Vanadium Pentoxide Nanostructures for High Performance Polymer Solar Cells

Solar energy, with features like interminable is the most promising technology to solve the energy crisis. In recent years, bulk heterojunction polymer solar cells (BHJ PSCs) have become very popular. Many efforts have been devoted to developing BHJ PSCs due to their great low specific weight and compatibility with flexible substrates [۱]. BHJ PSCs consist of three main substrates: anode, photoactive layer and cathode. The other two components which improve the PSCs' performance are the electron transport layer and the hole transport layer (HTL). The HTL task is to improve the anode's efficiency in collecting the holes in PSCs. The HTL should have good stability, high electrical conductivity, low resistance and high working function. For current PSCs with indium tin oxide (ITO) as the anode, PEDOT:PSS has been widely used as the HTL due to its high work function and smoothing out the rough ITO. Unfortunately, the strong acidity of PEDOT: PSS causes problems such as degradation of cell stability [۲]. VOx is a promising candidate due to its relatively high charge transfer mobility and environmental stability. Vanadium Pentoxide (V۲O۵) has special applications in different fields, such as optical detectors, light-converting devices, lithium-ion batteries and solar cells. V۲O۵ can be synthesized using different methods such as hydrothermal, sol-gel and electrodeposition [۳, ۴]. In this work, V۲O۵ nanostructures were grown on the ITO-coated glass slides using differential pulse voltammetry (DPV) method and utilized as the interfacial layer in the construction of BHJ PSCs. The influences of deposition time and applied potential were investigated. Simple adjustment of the applied potential regime and deposition time led to considerable structural and electrochemical changes of the resulting V۲O۵. Features of the electrochemically-grown V۲O۵ were compared with each other. The best sample was selected in terms of suitable surface conductivity, high optical transparency and appropriate energy levels and applied as HTL in BHJ PSCs. Results revealed that the optimum V۲O۵ sample provided considerably better electrical, optical and electrochemical features. V۲O۵ nanoparticles synthesized with DPV, showed the high electroactive surface area (۰.۲۶ cm۲), high charge mobility (۲.۴۴×۱۰-۴ cm۲.V-۱s-۱) and excellent conductivity (۰.۰۳ mS.cm-۱). The best cell provided an open circuit voltage of about ۰.۵۶ V, a short circuit current of ۹.۴۲ mA cm۲, a fill factor of ۶۵.۳% and a PCE of ۳.۴۰%. PCE of this cell was about ۶۰% higher than that considered for the reference device prepared base on the PEDOT:PSS HTL.