The Chinese Academy of Sciences said this week that its researchers have fabricated homogenized perovskite films that could increase the efficiency and stability of perovskite solar cells.
The scientists said they addressed the typical phase segregation issue that inevitably takes place inside perovskite films and affects both the power conversion efficiency and thermal stability of perovskite PV devices. This is a troublesome issue, with illumination, such as sunlight, disrupting the delicately arranged composition of elements within mixed-halide perovskites.
“We all know from previous work that cations in different groups are distributed inhomogeneously, but how exactly these cations are distributed and the reasons behind it and how it affects efficiency remain unclear,” said researcher Xu Pan. “We visualized the out-of-plane compositional inhomogeneity along the vertical direction across the perovskite films and identified the underlying reasons and the potential impacts for devices.”
The researchers said in “Out-of-plane cations homogenize perovskite composition for solar cells,” which was recently published in Nature, that they measured the vertical distribution of cations FA+ and Cs+ in the film. They discovered Cs+ aggregation at the film's bottom and FA+ concentration at the upper interface.
“Then we found that cations in different groups crystallize and transform at very different rates,” said Pan, in reference to the main cause of the film inhomogeneity.
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In order to create more homogeneous films, the group used an additive known as 1-(Phenylsulfonyl)pyrrole (PSP), which they said successfully fulfilled its mission.
With the optimized perovskite film, the academics built a solar cell with an active area of 1 cm2. Tested under standard illumination conditions, this device showed a power conversion efficiency of 26.14%, an open-circuit voltage of of 1.164 V, a short-circuit current of density of 26.14 mA/cm2, and a fill factor of 85.74%. The cell was also able to retain 92% of its original efficiency after 2,500 h.
The scientists also said that an undisclosed third-party entity has certified the cell efficiency at 25.2%.
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