Optimal design, fabrication and characterization of scalable, fullerene-free organic solar cells using roll-processing

The Sun can provide us with a virtually infinite amount of energy, and this is why solar cells represent one of the leading technologies for renewable energy harvesting. Among those, organic photovoltaics (OPVs) have the benefit of short energy payback times and high manufacturing speeds using large-scale roll-to-roll processing at ambient temperatures. However, they are not yet competitive on the market due to their insufficient stability and efficiency, but recent progress on non-fullerene acceptor materials has made it possible to overcome the 15% PCE mark in lab-scale devices. The aim of the project is to obtain a device with the highest possible efficiency using only scalable techniques. This is done by optimizing the chosen active layer, hole transport layer and back electrode depositions on top of a flexible substrate. The main fabrication techniques used are slot-die coating, thermal evaporation and flexographic printing. The study of the optimal active layer is conducted on a system based on a combination of a polymer, P3HT, and a small molecule, O-IDTBR. Our study is conducted by varying the solvents of the active layer solution, the temperature of the bed and the slot-die head during the deposition, and the thickness through the coating parameters (speed and flow rate). The hole transport layer study will be focused on PEDOT:PSS of different viscosities, varying the thickness of the layer. Finally, Ag, Cu and Au are tested for electrode purposes and compared to cheaper, open-air printed Silver paste, as well as different techniques for their deposition. Characterization of the final devices includes testing under a Sun simulator, EQE and transmittance measurements, as well as electrical characterization. The study is enriched with AFM images to get insight on the nanostructure of the active layer.