Solution processing is the most appealing aspect of organic photovoltaic (OPV) devices. The possibility of printing low‐cost, lightweight, and efficient polymer solar cells (PSC) is the commonly accepted paradigm associated with printable materials deposited as inks using solution‐processing techniques. In addition to slot–die, serigraphy, and flexo/gravure printing, spray coating can be used for photo‐active polymer blends, interface materials for hole and electron extraction, and electrodes. This technique is widely accepted in the industrial world as one of the most suitable for coating thin layers onto virtually any kind of substrate (e.g., glass, metal, plastic) with a degree of conformability insuperable by any other high‐speed coating technique. We present the basic principles governing the mechanisms of atomization, the main techniques adopted for PSCs, the state of the art applications of spray coating for building up each layer of a PSC, and an overview of the perspectives for industrialization.
In organic photovoltaics, large-area-compatible and solution-based processes are the best candidates for achieving high throughput at low cost. Among these, spray coating is a well-established technique in the industry that can be successfully applied to polymer solar cells (PSCs). In this study we report the demonstration of an automated spray process, completely performed in air, to fabricate the first fully spray-coated modules on glass/transparent-conducting-oxide (TCO) substrates. For this purpose we started with optical and electrical characterization of single layers (TiO2, P3HT:PCBM, PEDOT-CPP, and PEDOT-PH1000), to obtain films with the desired properties. Then, photovoltaic cells and modules were fabricated by increasing the number of sprayed layers (1-layer, 2-layers, and fully sprayed devices completely free from evaporation processes). Good reproducibility and encouraging electrical performances were obtained. In particular, the 1-layer, 2-layer, and full modules (active area= 6 cm(2)) exhibited conversion efficiencies of 1.8%, 1.3%, and 0.9%, respectively. Therefore, the feasibility of a scalable and reliable process for spraying all layers of a semitransparent PSC module were demonstrated here with the potential of being applicable to plastic substrates by the introduction of a low-temperature-processed layer in place of TiO2
The use of environmental friendly solvents for the fabrication of solution processed organic photovoltaics is a key issue to scale up the technology. Nowadays however, toxic and harmful chlorinated solvents are largely used in polymer solar cell laboratory research. In this work we successfully reached high solubility and miscibility of the low band gap polymer Poly [[4,8-bis[(2-ethylhexyl)(PBDTTT-E-F, commonly known as PTB7), blended with [6,6]-Phenyl-C71-butyric acid methyl-ester ([70] PCBM fullerene derivative) in a non-chlorinated solvent (Dimethylbenzenes also known as Xylenes). We studied the solar cells realized depositing blend solutions based on various Xylenes (ortho, para and an isomeric mixture from technical grade) achieving high power conversion efficiencies up to 8.7%.
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