An international research group has fabricated an inverted perovskite solar cell based by using polymer to improve the low-defect crystallinity of the perovskite film. Dipoles, which are molecules with opposite charges on the ends, are commonly used in solar research for interfacial engineering strategies in organic and perovskite solar cells.
The scientists built the solar cell with an active area of 9.6 mm2 and a p-i-n structure, which means the perovskite cell material is deposited onto the hole transport layer, and then coated with the electron transport layer, unlike with conventional n-i-p device architecture. Inverted perovskite solar cells typically show strong stability, but lag behind conventional devices in terms of conversion efficiency and cell performance.
The researchers said that dipoles on the perovskite surface can suppress ion migration, while facilitating interfacial charge extraction and enhancing hydrophobicity. They used a type of dipole known as b-pV2F and said it enabled a more compact perovskite film with an enlarged grain size of around 480 nm.
“Atomic force microscopy images showed that b-pV2F reduced the surface roughness from 54.4 to 41.1 nm, which is expected to ameliorate coverage with charge-transporting layers,” they said.
The team measured the entire film formation process via grazing incidence wide-angle x-ray scattering (GIWAXS) and found that b-pV2F controls the perovskite crystallization by reducing perovskite formation energy, which results in a more ordered crystal structure. The cell configuration features a glass/indium tin oxide (ITO) substrate, an electron acceptor made of phenyl-C61-butyric acid methyl ester (PCBM), a perovskite layer, a phenyl-C61-butyric acid methyl ester (PCBM) layer, and a silver (Ag) metal contact.
The device achieved a power conversion efficiency of 24.2% under standard illumination conditions, an open-circuit voltage of 1.18 V, a short-circuit current of 24.8 mA/cm2 , and a fill factor of 84.3%. The Shanghai Institute of Microsystem and Information Technology (SIMIT) confirmed the results.
“The stability of unencapsulated devices under working conditions shows that target perovskite solar cells retain 96% of the initial power conversion efficiency after continuous maximum power point tracking for 1,000 hours,” the scientists said.
They described the cell technology in “Highly efficient p-i-n perovskite solar cells that endure temperature variations,” which was recently published in Science. The research group includes academics from Helmholtz-Zentrum Berlin (HZB) and the University of Stuttgart in Germany, the Chinese Academy of Sciences, and Swansea University in the United Kingdom.
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