Coating Technique Uses Solution, Not Heat, to Create OPV Interlayers

Researchers have developed a spin coating technique to create zinc-related oxide (ZnOx, ZnOHx) ultrathin films (ceramic films) for use as buffer layers for organic photovoltaic (OPV) cells. Buffer layers, also called OPV interlayers, separate electrons from the holes produced by light energy and transport electrons and holes to each electrode in an OPV.

Scientists from Osaka University and Kanazawa University collaborated on the coating technique for ZnOx, ZnOHx. They deposited the films in a solution process using the metal organic decomposition (MOD) method at ambient temperature and pressure without a heating process. The thin films obtained from the precursor concentrations tuned with ethanol dilution were analyzed by UV-VIS, XPS, UPS, and AFM measurements.

Organic photovoltaic solar cells and schematic figure of the cell structure. Current density voltage (JV) characteristics during light irradiation and dark condition. Courtesy of Osaka University.

“We succeeded in forming nano-size oxide ultrathin films by our blended solution coating method without heating,” said professor Tohru Sugahara.

The team demonstrated that thin films produced with this technique could be used as buffer layers for OPV cells. The films achieved a power conversion efficiency (PCE) equivalent to that of ZnO thin films produced by conventional methods involving sintering. Researchers reported the highest PCE under any use of an ultrathin film of about 20 nm. The thickness of the team’s ultrathin film can be controlled in the range of 5 to 100 nm.

This technique could reduce the cost and shorten the production process for OPV cells, which are fabricated using low-cost roll-to-roll printing processes. The research team anticipates that their amorphous ZnOHx film will be recognized as a candidate for future devices using OPVs.

PV cells using organic compounds have several advantages: they are lightweight, flexible, and sophisticated, and their production cost is low. For these reasons, they are anticipated to be next-generation PV cells.

The research was published in Scientific Reports (doi: 10.1038/s41598-018-27953-6).