3.2 Towards the sustainable, industrial fitting fabrication of cellulose based, flexible organic solar cells using spray deposition

In future functional designs of electronic devices such as a bulk hetero junction (BHJ) organic solar cells (OSC), the use of environmentally friendly materials as well as the implementation of sustainable production processes are as topical than ever. Wood based cellulose nanofibrils (CNFs) are biodegradable, lightweight, flexible, and strong, making them a suitable candidate for replacing synthetic polymers in the fabrication of flexible composite materials. Spray deposition is a fast and easy to implement technique: The preparation of thin, homogenous films of large scale and with ultra low roughness as well as the functionalization of cellulose films is possible. Here, spray deposition was used to transform the standard BHJ OSC model into a sustainable, thin and flexible alternative using CNF as template, flexible silver nanowires to replace the brittle ITO, conductive poly(3,4 ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) as electron blocking layer and a mixture of poly(3 hexylthiophene) (P3HT) and [6,6] phenyl C61 butyric acid methylester (PCBM) as active layer. Toxic standard solvents were exchanged with green alternatives. The resulting layers were characterized using SEM, AFM, grazing incidence small angle Xray scattering (GISAXS), and four point measurements. The resulting insights show among other things the beneficial templating effects of CNF, leading the way towards a sustainable production route for BHJ OSCs.