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Chinese researchers claim to have built a perovskite solar cell capable of effectively reducing ion migration and offering superior stability. The device uses an ultra-thin membrane made of a polymeric material known as PDTBT2T-FTBDT (D18), which purportedly offers conformal coverage on the surface of the perovskite film due to its high fluidity.
Scientists at Chinas Huaqiao University have designed a perovskite solar cell that uses a hole-selective interlayer that inhibits ion diffusion to increase device stability.
Ion migration is considered to be the main cause of instability in perovskite solar cells. It occurs when the soft crystal lattice and relatively weak bonds of the perovskite film lead to low defect formation energies, so heat and light could easily activate ionic defects within the perovskite lattice. The accumulation of ions deforms the local crystal structure and degrades the perovskite film, both the electron transport layer (ETL) and hole transport layer (HTL), as well as the electrodes.
“The idea of ??incorporating a hole-selective interlayer in perovskite solar cells was inspired by proton exchange membrane (PEM) fuel cells, where the PEM acts as a proton conductor while blocking the diffusion of other chemical species,” the researchers explain. “Designing internal barriers that block ion diffusion between layers is of vital importance to improve the lifetime of perovskite solar cells.”
The research team constructed the hole-selective interlayer using an ultrathin polymeric material known as PDTBT2T-FTBDT (D18), which reportedly offers conformal coverage on the surface of the perovskite film due to the high fluidity of its dilute solution. It also exhibits coincident energy level alignment with the perovskite absorber and the Spiro-OMeTAD HTL.
The researchers deposited the interlayer by spin-coating a hot chlorobenzene (CB) solution of D18 onto the perovskite film, which reportedly led to the formation of a dense membrane. They constructed the solar cell with a glass substrate and fluorine-doped tin oxide (FTO), a tin oxide (SnO2)-based ETL, a perovskite absorber, the D18 interlayer, the Spiro-OMeTAD HTL, and a gold (Au) metal contact.
The group evaluated the effectiveness of the interlayer in preventing ion diffusion and found that it outperformed the most commonly used polymers P3HT and PTAA. “The results show that the D18 layer has a strong ability to block ions under thermal stress conditions,” he explains. “D18 is in close contact with the perovskite grain and the grain boundary, providing conformal coverage.”
The proposed 0.12 cm2 solar cell was tested under standard lighting conditions and achieved a power conversion efficiency of 26.39%, an open-circuit voltage of 1.185 V, a short-circuit current of 26.54 mA cm-2, and a fill factor of 83.92%. In comparison, a reference cell built without the D18 layer achieved an efficiency of 24.43%, an open-circuit voltage of 1.152 V, a short-circuit current of 26.39 mA cm-2, and a fill factor of 80.37%.
“We have shown that the introduction of the D18 polymer interlayer can effectively block layer-to-layer ion diffusion inside perovskite solar cells while maintaining highly efficient hole transport, leading to significantly improved stability of the nip cells with a certified efficiency of over 26%,” the researchers said, noting that the cell was also able to retain 95.4% of its initial efficiency after 1,100 h.
They also claimed that the device is currently the “most stable” perovskite solar cell with high levels of efficiency.
The new cell concept was presented in the study “ Ultrathin polymer membrane for improved hole extraction and ion blocking in perovskite solar cells,” recently published in Nature Communications . |
