Spray-Coating Technique And Cheap Organic Solar Cells

(a) Schematic build-up of the organic solar cell, (b) SEM and (c) FIB/TEM cross sections of the polymer solar cell with a spray coated Ag top contact. (IMEC)

IMEC of Leuven, Belgium has demonstrated a solution-processed organic solar cell with a spray-coated active layer and a metal top contact spray-coated on top. The resulting cell shows power conversion efficiencies above 3%.

The cell's performance is comparable to organic solar cells produced by spin coating of the organic layer and vacuum evaporation of the top contact metal. This is an important step towards producing organic solar cells with cheap and large-area processes.

Polymer-based (organic) solar cells hold the promise of low-cost production and a high throughput. However, this can only be achieved if all the layers of the cells can be deposited by solution-based, in-line compatible methods. IMEC’s research shows that spray-coating is a suitable deposition technique, and that it can be used to deposit all layers, including the metal top contact.

Spray-coating is a large-area deposition technique for a variety of surfaces with different morphologies and topographies. It is often used for industrial coating and in-line deposition processes. In spray-coating systems, the ink is atomized at the nozzle by pressure or ultrasound and then directed toward the substrate by a gas. An added advantage of spray-coating is its efficiency - compared to other techniques only a small amount of the solutions are wasted.

The active layer deposited with spray-coating that showed power conversion efficiencies above 3% was a solution of P3HT and PCBM. The metal top contact was spray-coated with a solution containing silver nanoparticles. IMEC demonstrated that spray-coating greatly reduces the damage to underlying layers compared to other techniques. The silver nanoparticles were sintered at 150°C, a temperature that is compatible with processing on flexible substrates.

(IMEC)