Application of biodegradable substrates and inkjet printing in dye-sensitized solar cells

Abstract

Dye-sensitized solar cells (DSSCs) are electrochemical devices, which convert photon energy to electrical energy and they are promising alternative power unit candidates for small-scale electronics. Despite of efforts devoted to the research of DSSCs, the integration of efficient devices onto cellulose-based substrates is yet to be achieved, due to the challenging liquid electrolyte within the device. Additionally, the precursor wastage produced during the manufacture of solution processable layers, uncontrolled levels of deposition and layer positioning as well as the dependence on the pre-drilled glass substrates are not practical for many applications. The aims of this work were to determine the consequences of replacing the conventional counter electrode (CE) and glass substrate with a cellulose based alternative. Moreover, an assessment of the introduction of the inkjet printing method into the device fabrication was also performed. In first part of this thesis, alternative CEs were produced on a laminated cellulose sheet by first coating it with a carbon nanotube ink and subsequently p-toluenesulfonate doped poly(3,4-ethylenedioxythiophene) ink. The new CEs exhibited flexibility and low charge transfer resistance. Additionally, the cells produced with these CEs demonstrated only a 20% less efficiency compared to the reference cells with glass/fluorine-doped tin oxide (FTO)/platinum (Pt). The remainder of the thesis was devoted to the inkjet printing of the dye and Pt layers as well as the electrolyte of DSSCs. Initially, the three most popular electrolytes in DSSC research were characterized in terms of their physiochemical properties. Subsequently, the least dilatant electrolyte was inkjet-printed on sensitized mesoporous oxide to produce DSSCs. Thanks to this method, the device fabrication sequence was simplified and the device containing inkjet-printed electrolyte exhibited enhanced stability and less resistive losses. The conventional way of sensitizing mesoporous oxide surface entails exposure to a dilute solution of dye for long hours. In addition to the environmental burden of wasting ruthenium based dyes, the accuracy in the position and amount of the dye layer is uncontrolled. In order to overcome all these aforementioned challenges, inkjet printing was proposed as a new method for the sensitization step and the cells with inkjet-printed dyes provided the opportunity for tailor-made devices of various colors with tuned intensity. Pt, traditional catalyst for the DSSCs, is deposited by casting a drop on the FTO coated glass substrates for the lab-scale production of DSSCs, however it is both an expensive and is currently defined by the EU as a critical metal resource. In order to minimize Pt wastage and create precisely patterned catalyst layers with custom-made transparency, inkjet printing of Pt precursor was investigated. The cells with inkjet-printed catalyst exhibited a similar performance and stability to the reference cells.