Even though current perovskite-silicon solar cells excite the PV industry with high-power conversion efficiencies exceeding 33 percent in the laboratory, their large-scale production remains challenging. “Successfully applying the perovskite materials with scalable technologies on the silicon bottom cell has been a break-through for us”, said Oussama Er-raji, doctoral student and project lead at Fraunhofer ISE. “An a two-step hybrid process, the inorganic components of the perovskite absorber are first evaporated, followed by the blade-coating of the organic components. This makes it suitable for a production on an industrial scale.”

The scientist demonstrated fully textured perovskite silicon tandem solar cells with open-circuit voltages exceeding 1900 millivolts and efficiencies of 27,8 percent. Furthermore, they found that the coating speed in the hybrid evaporation/blade-coating process does not affect the perovskite thickness, unlike in one-step blade-coated perovskites, but it correlates with the perovskite conversion rate, which has been key for the optimization of the absorber.

With this study the Fraunhofer ISE researchers built on their extensive experience with the hybrid route, which combines evaporation with a wet-chemical process step. While in the past spin-coating had been used for the wet-chemical step, they were now able to transfer their experience to the more scalable blade-coating for the 2^nd step.

Many perovskite research groups, including KAUST and Fraunhofer ISE, investigate pathways that would allow perovskite-silicon tandem solar cells to go into mass production. So far, perovskite-silicon solar cells are mostly produced by spin-coating. “Spin-coating is great as a lab technique as it is very flexible and allows for rapid testing of new materials, additives and process parameters. For large scale production it is however not suitable”, said Dr. Juliane Borchert, group lead on Perovskite Materials and Interfaces at Fraunhofer ISE. “We also expect that the learnings about the dynamics during blade-coating can be transferred to slot-die-coating which is even more suitable for scaling”, Borchert added.

Silicon solar cells can convert a physical maximum of 29.4 percent of sunlight into electricity. To continue making increases in solar cell efficiency, solar researchers around the world are turning to tandem photovoltaics, especially the combination of a silicon bottom and a perovskite top cell. While the silicon solar cell primarily converts the red portion of sunlight efficiently into electricity, a top sub-cell made of perovskites, can better utilize the blue fraction of light.