Electrodeposition of PEDOT perchlorate as an alternative route to PEDOT:PSS for the development of bulk heterojunction solar cells

Bulk heterojunction (BHJ) solar cells were fabricated employing different poly(3,4-ethylenedioxythiophene) (PEDOT) buffers: one deposited by electrochemical potentiostatic synthesis (perchlorate as counterion) and the other by casting a commercial polymer (polystyrene sulfonate, PSS, as counterion) on indium tin oxide (ITO) electrodes. The experimental conditions to electrosynthesize the PEDOT film and control its thickness were successfully investigated. [6,6]-phenyl-C61 butyric acid methyl ester (PCBM) was used as electron acceptor in the blend. As electron donor, either the regioregular poly(3-hexylthiophene) (P3HT) or a polythiophene copolymer, functionalized with a porphyrin derivative to improve the absorption of the layer in the visible range, was employed. The morphologies of the PEDOT and the photoactive layers were extensively investigated by atomic force microscopy. The performances of all devices were tested evaluating the power conversion efficiencies which resulted comparable when either PEDOT:ClO4 or PEDOT:PSS was used as buffer layer. That proves electrochemical deposition of PEDOT can represent a good alternative to casting for the production of solar cells, since it is less expensive and permits an excellent control of the layer thickness.