Researchers at King Abdullah University of Science and Technology (KAUST) and Max Planck Institute have developed an inverted perovskite-silicon tandem solar cell with a 1 nm thick interlayer based on magnesium fluoride (MgFx) placed between the perovskite layer and the hole transport layer (HTL), in order to reduce voltage losses while still retaining 95.4% of its initial efficiency after 1,000 hours.
The scientists stated that the charge transport and recombination interfaces could be carefully tuned with MgFx interlayers, enabling a certified efficiency of 29.3%. Currently, the record perovskite/silicon tandem solar cell is a 29.8% device that was recently developed by scientists at Helmholtz-Zentrum Berlin (HZB) in Germany. The scientists fabricated the new cell with a sub-cell based on crystalline silicon wafers with double-side texture, which they say reduces front reflection while improving light trapping. They also placed the MgFx interlayer at the electron-selective top contact.
They used buckminsterfullerene, a molecule which is also known as C60, for the fabrication of the HTL, and added a tin(IV) oxide (SnO2) layer and an indium tin oxide (IZO) top contact. The Sno2 layer acts as a buffer against damage from the sputtering of the IZO top contact. This IZO-perovskite structure, according to the researchers, supported a very slow carrier decay process and improved charge extraction.
The scientists tested an encapsulated solar cell built with this architecture at the CalLab of the Fraunhofer Institute for Solar Energy Systems (Fraunhofer ISE) in Germany. The device achieved a steady-state power conversion efficiency of 29.3% and a reverse-scan efficiency of 29.4%. It also achieved an open-circuit voltage of 1.85 V, a short-circuit current of 19.8 mA/cm2, and a fill factor of 77.9%.
The researchers explain the device statistics corroborated that the power conversion efficiency improvement was mainly the result of enhanced open-circuit voltage and fill factor. The cell went through damp-heat testing and was able to retain 95.4% of its initial efficiency after 1,000 hours.
“The open-circuit voltage even improved slightly, indicating that the perovskite itself and the interfacial layers were sufficiently tolerant to thermal stress,” the research team said.