Researchers from the University of North Carolina have developed a mini perovskite solar module with a power conversion efficiency of up to 19.3% efficiency based on a novel approach for interface engineering.

The new device was created using a new technique for stabilizing the embedded perovskite-substrate interfaces in the solar cells. Common approaches, the researchers explained, had previously focused on stabilizing perovskite-metal electrode interfaces through surface passivation or post-fabrication treatment. “Degradation of perovskite solar cells starts from the interfaces, including both perovskite-metal electrodes and perovskites-substrates, where defects enrich,” the team stated in the new paper. “Stabilizing the embedded bottom interfaces is as important as that of [the] top interface.”

The research group found that a high density of voids is concentrated around these interfaces and that the perovskite around these voids is subject to faster degradation. Their formation is attributed to the presence of dimethyl sulfoxide (DMSO), which is a non-volatile solvent that is commonly used to improve perovskite film morphology near the bottom of perovskite films.

The solvent was replaced with a solid-state, lead-coordinating additive of carbohydrazide (CBH), which the scientists say was able to reduce the formation of the voids and, at the same time, to act as an effective reductant agent for the detrimental iodine formed in the perovskite material. “CBH barely evaporated during thermal annealing and thus remained within the perovskite films,” the team explained.

The new additive reportedly enabled the fabrication of perovskite solar cells with a stabilized efficiency of 23.6%, an open-circuit voltage of 1.17 V, a short-circuit current density of 24.1 mA/cm-2, and a fill factor of 0.842. The perovskite films used for the cells were prepared with a room-temperature blade-coating method.

These cells were then used by the scientists to produce mini modules with efficiencies of 19.3 and 19.2%, with aperture areas of 18.1 and 50cm2, respectively. These results were certified by the U.S. Department of Energy's National Renewable Energy Laboratory (NREL), which tested 112 mini panels sent by the UNC research team. More than half of the devices exhibited efficiencies of over 19% and around 77% of them over 18.5%. “Furthermore, the long-term operational stability of the highly efficient perovskite mini-modules was also tested with the statistical results,” they stated. “Five mini modules retained 85% of initial power conversion efficiencies after 1,000 hours of light-soaking under simulated 1-sun illumination at 50 degrees Celsius.”