Polymer Solar Cells based on Benzodithiophene copolymers

Polymer solar cells are widely seen as the promise to a cheap alternative to the silicon-based ones. In addition to their low costs, they also have other advantages such as light weight, easy processability and compatibility with large scale flexible substrates, which make them suitable for a wide range of applications. However, the efficiency of photovoltaic energy conversion for these plastic devices is still low and this is limiting their commercial use. The efficiency of these polymeric photovoltaic cells got a significative increase when the bulk heterojunction (BHJ) configuration was introduced: it consists in an interpenetrating network of electron donor and acceptor materials that largely increases the active area and diminishes the distance that charge carriers have to travel. Recently, benzodithiophene (BDT) based polymers (Fig.1) have been used as electron donors in polymer solar cells showing very promising properties such as an increased charge transport and a red shift on the absorption spectra. In this work, the synthesis of different regioregular copolymers having substituted BDT as one of the monomers are described. The obtained polymers are characterized by spectroscopic and electrochemical techniques. Energy conversion measurements of BHJ solar cells produced with these polymers were conducted, and the electrical performances were compared in order to study the influence of the different comonomers on the overall efficiency of the devices.