Cooling and time in the dark preserves perovskite solar power
A study has found both the cause and a solution for the tendency of perovskite solar cells to degrade in sunlight, a breakthrough potentially removing a roadblock to commercialization for this promising technology. Researchers found those degraded devices exhibit self-healing powers when given a little time in the dark.
The team determined that photo-degradation in perovskite cells is a purely electronic process due to charge accumulation without chemical damage to the crystal structure and therefore can be reduced, while the cells' self-healing properties allow them to rebound in the dark.
"We can stabilize the device performance by controlling the environmental temperature," said Wanyi Nie, lead researcher on the paper published today in Nature Communications. "The degradation of the devices can be suppressed by simply lowering the temperature by few degrees, that is, from 25 degrees Celsius to 0 degrees Celsius."
The team, lead by Aditya Mohite from the Los Alamos "Light to Energy" team in the Material Synthesis and Integrated Devices group, is exploring organometallic halide semiconducting perovskite solar cells. They are promising because of their high power conversion efficiency (PCE) exceeding 20 percent and the low fabrication costs, the perovskite material is synthesized via a low-temperature solution process.
While achieving high PCE is important, the successful transition from a proof-of-concept experiment to actual market-viable photovoltaic technology requires the device to operate with stability under continuous sunlight, of course, and in the air and humidity of outdoor conditions.
The problem of stability against ambient air/humidity can be circumvented through encapsulation schemes, but the photo-stability of the perovskite-based devices remained an open question. As noted in the literature, these solar cells will undergo degradation with constant light soaking even when the device is under vacuum. Such degradation over time with solar illumination could undermine the commercialization of perovskite-based solar cells.
The new paper, "Light-activated photocurrent degradation and self-healing in perovskite solar cells", co-authored by Wanyi Nie and Jean-Christophe Blancon, describes the photo-degradation process. "What we found in this study is that under constant 1-sun illumination the large-grain perovskite solar cells degrade majorly in terms of the photocurrent," Nie said. "But what's interesting is that the devices can self-heal when sitting in the dark for a short while."