Researchers from Germany's Karlsruhe Institute of Technology (KIT) have developed a scalable two-step evaporation and inkjet process for perovskite thin-film solar cells. The new technique is said to enable champion cells with the same efficiencies as those made with the spin coating process.
The process is described as a scalable and reliable technique for high-quality perovskite deposition, which combines the use of an evaporated lead iodide layer with inkjet-printed organic perovskite precursor materials. It is also said to exhibit high reproducibility and potential for conformal growth on textured silicon, and that provide films that are free of drying effects and toxic solvents.
The team explained that it was challenging to improve the performance of solar cells based on evaporated lead iodide to the same performance levels of devices with spin-coated lead iodide scaffold. The scientists were able to tailor porosity with an inexpensive dimethyl sulfoxide (DMSO) vapor treatment, as they identified that the porosity of the lead iodide in the first step is crucial for the conversion in the resulting two-step fabrication process.
In the proposed technique, the films were deposited using a Pixdro LP50 inkjet printer from German supplier SÜSS, equipped with a Sapphire QS-256/10 AAA print head, which has 16 times more nozzles than typical print heads used in labs for this type of application. This both helps to increase the droplet-surface interaction time, which is necessary to prevent large-area drying effects, and also reduces the probability of pinholes.
Referring to the Sapphire print head used in the study, KIT's next-generation PV group leader, Ulrich W. Paetzold, pointed out it can also be used in larger printers, such as the n.jet lab from Notion Systems, capable of printing areas of 0.61 x 0.61 square meters at a speed of 2 meters per second.
By optimizing the printing parameters, the group achieved champion devices with an efficiency 18.2%, which it noted is “on par with spin-coated counterparts”. The scientists said that the spin-coated reference devices were still slightly better in performance compared to the scalable processes, however. The optimal results in this study were attributed to the morphology of the lead iodide thin film and the selected resolution of the printing process, as well as the intermixing and stoichiometry step enabled by the DMSO vapor treatment to increase the lead iodide porosity.
Going forward, the team will be working on integrating the process into the fabrication of tandem devices and large area devices.
