Researchers from Korea University have fabricated an inverted perovskite solar cell by introducing an electron-accepting interlayer at the interface between the perovskite layer and the electron transport layer.
The cell has 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 – the opposite way round to conventional n-i-p device architecture. Inverted perovskite solar cells typically show strong stability, but have lagged behind conventional devices in terms of conversion efficiency and cell performance.
The scientists built the electron-accepting interlayer with a light-harvesting material known as 3,4,9,10-perylenetetracarboxylic diimide (PDI) and carbon black (CB), a 3D cluster compound composed of boron, carbon, and hydrogen atoms. They varied the thickness of the PDI–Cb interlayer from 0 to 3.0 nm.
The Korean group built the cell with an indium tin oxide (ITO) substrate, a solution based on poly(triaryl)amine (PTAA), which is an excellent hole transporting and electron blocking material, the perovskite layer, the PDI–Cb interlayer, an electron transport layer made of buckminsterfullerene (C60), a bathocuproine (BCP) buffer layer, and a silver (Ag) metal contact.
The academics measured the performance of the device under standard illumination conditions and found it achieved a power conversion efficiency of 22.31%, an open-circuit voltage of 1.16 V, a short-circuit current of 23.81 mA/cm2, and a fill factor of 80.70%. A reference device without the PDI–Cb interlayer reached an efficiency of 19.98%, an open-circuit voltage of 1.1 V, a short-circuit current of 22.86 mA/cm2, and a fill factor of 78.74%.
“The devices adopting PDI–Cb interlayer showed enhanced device performance with increasing thickness of the PDI–Cb interlayer and reached peak photovoltaic performance at the PDI–Cb thickness of 2.0 nm,” they explained. “The PDI–Cb interlayer acts not only as a good electron acceptor due to o-Cb unit but also as charge transport due to slip-stacked packing structure.
The scientists said the cell was also able to retain 91.7% of its initial efficiency after 1,000 h under standard illumination conditions.
They introduced the cell technology in the paper “Electron-Accepting PDI–Cb Interlayer for over 22% Inverted Perovskite Solar Cells with Photo- and Thermal Stability,” which was recently published in RRL Solar.
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