Design Modification Protects Perovskites

Solar cells based on a family of light-absorbing trihalides with the perovskite structure can be protected from atmospheric degradation by a simple device design modification, according to a study in Energy Technology (2015, DOI: 10.1002/ente.201500045). Photovoltaic devices featuring (CH₃NH₃)PbI₃ and related perovskite compounds have grabbed headlines in the past two years because of the exceptional rate at which their performance has been improving. But these cells’ future is uncertain because they degrade quickly: Heat and humidity decompose the trihalide compound. Michael Grätzel of ETH Lausanne, together with colleagues in Saudi Arabia and China, may have a way to stop the degradation. The team did away with the film of positive-charge-conducting material and metal electrode that covers a perovskite-infused titania layer in typical cell designs. Instead, they coated the titania with a film of zirconia and topped that layer with carbon. Cells featuring that design performed well and did not degrade during a weeklong outdoor test in Saudi Arabia and a three-month indoor test during which the cells were subjected almost continuously to temperatures above 80 °C.