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Chinese researchers have designed an inverted perovskite solar cell with a new strategy aimed at optimizing the lower region of the cell. The proposed cell was treated with two molecules known as 2-mercaptoimidazole and 2-mercaptobenzimidazole and was based on a hole transport layer dependent on a self-assembled monolayer.
A group of scientists led by Chinas Jiaxing University has developed an inverted perovskite solar cell based on a hole transport layer (HTL) with a self-assembled monolayer (SAM).
Inverted perovskite cells have a device structure known as a “pin,” in which the selective p-hole contact is at the bottom of the intrinsic perovskite layer i with the electron transport layer n on top. Conventional halide perovskite cells have the same structure but inverted: a “nip” arrangement. In the nip architecture, the solar cell is illuminated through the electron transport layer (ETL) side; In the pin structure, it shines through the surface of the HTL.
“The HTL prepared with SAM materials not only exhibit negligible parasitic absorption, low material consumption, and stable adhesion, but also exhibit inherent passivation of perovskite bottom defects,” the research team explained.
The researchers used two molecules known as 2-mercaptoimidazole (2-MeIM) and 2-mercaptobenzimidazole (2-MeBIM) as additives to HTL. According to them, these molecules interact with the phosphonate groups of the so-called MeO-2PACz, also known as [2-(3,6-Dimethoxy-9H-carbazol-9-yl)ethyl]phosphonic acid, inhibiting the aggregation of MeO-2PACz to the form a supramolecular structure, which in turn gives rise to a more homogeneous HTL.
The academics designed the cell with a glass substrate and indium tin oxide (ITO), a MeO-2PACz layer, the perovskite absorber, a phenylethylammonium bromide (PEA-Br) cation, an electron transport layer based on phenyl-C61-butyric acid methyl ester (PCBM), a bathocuproin (BCP) buffer layer and a silver (Ag) metal contact.
They tested the cells performance under standard lighting conditions and compared it to that of a reference cell without the additives. The champion solar cell treated with the additives achieved a power conversion efficiency of 24.38%, an open circuit voltage of 1.181 V, a short circuit current density of 24.43 mA cm-2 and a fill factor of 84.51%. The control device achieved an efficiency of 23.12%, an open circuit voltage of 1.166 V, a short circuit current density of 24.09 mA cm-2 and a fill factor of 82.32%.
“Thanks to the better energetic alignment of the target film, the HTL with additives showed a higher charge carrier extraction capacity,” the researchers explained. “The improved properties of HTLs with additives, such as greater homogeneity, conductivity and more aligned energy bands, and the improved background quality of the perovskite films, with a larger grain size and fewer defects, favor more charge transfer. effective and the suppression of energy loss by non-radiative recombination at the interface, which results in higher performance of perovskite solar cells.”
The cells treated with the additives were also able to retain more than 89% of their initial efficiency after 450 h, while the reference cell reached a value of only 74%. This was due to the higher quality of the perovskite film on the treated cells, which the group said minimizes their vulnerability to external and internal attacks.
The novel cell concept was presented in the study “ Synchronous modulation of hole-selective self-assembled monolayer and buried interface for inverted perovskite solar cells ,” published in Cell Reports Physical Science . |
