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An international team of researchers has developed an all-perovskite tandem photovoltaic device that reportedly exhibits reduced recombination losses in the cell’s bottom device and remarkable stability. To improve the surface of the perovskite solar cell, the scientists created partially non-conducting and non-functional regions that protect the perovskite region underneath from becoming defective.
A group of researchers led by the University of Toronto (Canada) has fabricated an all-perovskite tandem solar cell with a lower wide band gap cell based on tin-lead (Pb-Sn) perovskite with a limited amount of passivating defects and reduced interface recombination.
“Our work presents an effective strategy to improve the durability of this new photovoltaic technology, accelerating the practical application and commercialization of perovskite solar cells,” corresponding author of the research, Chongwen Li, told pv magazine .
“Our group has made great strides toward turning pure lead perovskites into a viable green energy source,” said Ted Sargent, a co-author on the paper. “However, Li’s method is conceptually different from previous studies. This research used diamine chelation chemistry directed at tin-containing perovskite, in which a metal ion forms a stable bond with a molecule that has two nitrogen atoms holding the metal. The method is new to the field of perovskite solar cells.”
“While previous work by Sargent’s group has attempted to decrease surface defects on perovskite, this time we created partially non-conducting and non-functional regions that protect the perovskite region underneath from becoming defective,” Li added. “We used a new chemical method to improve the surface of the perovskite solar cell. By adding diamine to the surface, we removed excess tin and adjusted the ratio of tin to lead to be more balanced. The diamine also created a stable barrier layer that helps protect the surface from atmospheric oxygen and heat.”
The research team built the tandem device with an indium tin oxide (ITO) glass substrate, a hole transport layer (HTL) of nickel(II) oxide (NiOx) and a phosphonic acid called methyl substituted carbazole (Me-4PACz), a broad bandgap perovskite absorber treated with 1,2-diaminopropane (DAP), an electron transport layer (ETL) based on buckminsterfullerene (C60), a gold (AU) metal contact, a PEDOT-PSS layer, a low-bandgap perovskite absorber, another ETL made of C60, a tin oxide (SnO2) buffer layer, and a metal electrode.
“The chelate barrier layer induces a more n-type doped perovskite film surface, with the work function shifted from about 4.81 eV to about 4.45 eV, which we expect to facilitate electron extraction and reduce nonradiative recombination at the interface, with a consequent improvement in the open-circuit voltage,” the scientists explain.
The performance of the DAP-treated tandem cell was tested under standard illumination conditions and was found to achieve an efficiency of 28.83%, an open-circuit voltage of 2.19 V, a short-circuit current density of 15.59 mA/cm2, and a fill factor of 83.4%. Furthermore, it was able to retain more than 90% of its original efficiency after 1,000 h of operation at full power under simulated illumination from an uncooled sun in air.
“Our diamine chelation strategy effectively suppresses oxidation and prolongs operational stability. This is because diamine chelation forms high-resistivity barriers, similar to the passivated emitter back-contact structure used in silicon solar cells,” concluded co-author Lei Chen. “These high-resistivity barriers provide a novel and effective passivation mechanism to stabilize and refine mixed tin-lead perovskite tandem solar cells, bringing this technology closer to commercialization.”
The novel approach was presented in the paper “ Diamine chelates for increased stability in mixed Sn–Pb and all-perovskite tandem solar cells ,” recently published in Nature Energy . The research group also included academics from the University of Toledo, the University of Washington, Lawrence Berkeley National Laboratory, the Georgia Institute of Technology and the University of Massachusetts Amherst in the United States, as well as King Abdullah University of Science and Technology (KAUST) in Saudi Arabia and Tohoku University in Japan. |
