Thermal stresses are key to long-term stability

Perovskite photo voltaic cells are extremely environment friendly and low price in manufacturing. Nonetheless, they nonetheless lack stability over the a long time underneath actual climate circumstances. A world analysis collaboration led by Prof. Antonio Abate has now published a perspective on this subject within the journal Nature Evaluations Supplies.

The researchers explored the results of a number of thermal cycles on microstructures and interactions between totally different layers of perovskite solar cells. They conclude that thermal stress is the decisive issue within the degradation of metal-halide perovskites. Primarily based on this, they derive essentially the most promising methods to extend the long-term stability of perovskite photo voltaic cells.

Perovskites are a large class of supplies with semiconducting properties appropriate for vitality conversion in a photo voltaic cell: one of the best of them, the metal-halide perovskites, already ship efficiencies of as much as 27%. The manufacturing of such thin-film photo voltaic cells requires significantly little materials and vitality, so photo voltaic vitality may develop into significantly cheaper. Nonetheless, when used outdoor, photo voltaic modules ought to present an almost secure yield for no less than 20 to 30 years. And right here, there’s nonetheless a number of room for enchancment in perovskite supplies.

Along with a staff led by Prof. Meng Li, Henan College, China, and different companions in Italy, Spain, UK, Switzerland and Germany, the researchers present that thermal stress is the decisive issue within the degradation of metal-halide perovskites.

Harsh circumstances in ‘actual life’

“When used outdoors, solar modules are exposed to the weather and the seasons,” says Abate. Whereas encapsulation can successfully defend the cells from moisture and atmospheric oxygenthey’re nonetheless uncovered to fairly giant temperature variations day and night time and all year long. Relying on the geographical circumstances, temperatures contained in the photo voltaic cells can vary from minus 40 levels Celsius to plus 100 levels Celsius (within the desert, for instance).

To simulate this, the perovskite photo voltaic cells within the research had been uncovered to rather more excessive temperature variations in a number of cycles: From minus 150 levels Celsius to plus 150 levels Celsius, and time and again. Dr. Guixiang Li (then a postdoc at HZB, now a professor at Southeast College, China) investigated how the microstructure inside the perovskite layer modified throughout the cycles and to what extent the interactions with the neighboring layers had been additionally affected by the temperature cycles.

Thermal stress contained in the perovskite movie and in between layers

Collectively, these elements have an effect on the efficiency of the cell. Particularly, the temperature cycles induced thermal stress, i.e. stress each inside the perovskite skinny movie and between the totally different adjoining layers: “In a perovskite solar cell, layers of very different materials need to be in perfect contact; unfortunately, these materials often have quite different thermal behaviors,” explains Abate.

For instance, plastics are likely to shrink when heated, whereas inorganic supplies are likely to increase. Which means in every cycle the contact between the layers turns into worse. What’s extra, native part transitions and diffusion of parts into adjoining layers have additionally been noticed.

Most promising technique

From this, the analysis groups have derived a technique to extend the long-term stability of perovskite photo voltaic cells. “Thermal stress is the key,” says Abate. The primary factor, subsequently, is to make the perovskite buildings and the adjoining layers extra secure in opposition to thermal stress, for instance by growing the crystalline high quality, but in addition through the use of appropriate buffer layers.

The scientists spotlight the significance of uniform check protocols for evaluating stability underneath temperature biking and suggest an method to facilitate comparability between totally different research.