Solution processing of back electrodes for organic solar cells with inverted architecture

Abstract

Solution processing of the electrodes is a big challenge towards scaling up and R2R processing of organic solar cells. Inkjet printing is a non-contact printing method, it can be realized by solution processing at ambient condition and provides freedom of shape in the electrode pattern. The inkjet and screen printing of the back electrode in organic solar cells with inverted architecture is investigated. To this purpose, different types of PEDOT:PSS hole transport layers were combined with ambient processed inkjet printed or evaporated Ag electrodes. The thickness of the PEDOT:PSS layer is the main factor determining the performance of the devices. A too thin layer of EL-P5015 PEDOT:PSS allows penetration of the solvents from the Ag ink, which leads to degradation of the devices and a drop in performance. To overcome this effect, a 1200nm thick layer of EL-P5015 is required. Alternatively, an aqueous based coating formulation of PEDOT:PSS (S305), can be combined with either inkjet printed or screen printed electrode at significantly reduced thickness down to 40nm. At the same time, the performance of these devices was comparable to devices with an evaporated electrode. Reducing the thickness of PEDOT:PSS layer from 1200nm to 40nm is a very efficient way to reduce the manufacturing costs of OPV devices. In addition, combining of thin PEDOT:PSS layer with an inkjet printed Ag grid structure allows manufacturing of semi-transparent devices.