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Researchers in Singapore have built a triple-junction tandem solar cell with an ultra-wide-gap perovskite absorber that integrates cyanate ions (OCN). The cell has surpassed previously recorded power conversion efficiencies for all other perovskite-based triple-junction tandems, as well as perovskite-silicon single-junction solar cells.
A research group at the National University of Singapore (NUS) has fabricated a perovskite-perovskite-silicon triple junction solar cell that integrates cyanate ions (OCN) into an ultra-wideband perovskite absorber (UWBG).
“The incorporation of OCN ions significantly reduces non-radiative recombination in the ultra-broadband perovskite film,” Yi Hou, lead author of the research, explained to pv magazine . “Therefore, cyanate-incorporated single-junction perovskite solar cells can achieve a higher open circuit voltage of 1.422 V compared to 1.357 V for conventional perovskite solar cells.”
The scientists explained that OCN can be a suitable substitute for bromide as a precursor material in the perovskite lattice structure. “Our research confirms the atomic-scale incorporation of OCN anions into the perovskite network,” Hou said. “Atomic resolution, low damage transmission electron microscopy (TEM) confirms for the first time the incorporation effect at atomic resolution. “It is also the first time that atomic resolution TEM images of an ultra-broadband perovskite hybrid film have been obtained.”
The academics fabricated the triple junction cell with a silicon bottom device with a heterojunction (HTJ) architecture, a middle perovskite solar cell, and a top perovskite cell integrating the UWBG perovskite absorber with 5% OCN content. .
The triple junction device had a structure that integrated the HJT cell, a glass substrate and indium tin oxide (ITO), a hole transport layer (HTL) based on a phosphonic acid called methyl-substituted carbazole (Me- 4PACz), a perovskite absorber with an energetic bandgap of 1.55 eV, an electron transport layer (ETL) of buckminsterfullerene (C60), a layer of tin (IV) oxide (SnO2), another layer of ITO, a HTL of nickel(II) oxide (NiOx) and Me-4PACz, the perovskite absorber UWBG, an electron transport layer (ETL) of buckminsterfullerene (C60), a layer of SnO2, an ITO layer and a fluoride lithium (LiF) as an inorganic ionic dopant.
“The UWBG perovskite evenly covers the central cell without obvious damage to the bottom layer,” the researchers explain. “The smooth top surface and robust performance of the double-junction half-cell create an ideal substrate for subsequent deposition of UWBG perovskites.”
Tested under standard lighting conditions, the triple junction cell achieved a maximum efficiency of 27.62%, an open circuit voltage of 3.132 V, a short circuit current density of 11.58 mA/cm2, and a fill factor of 76.15%. In comparison, a reference device without the incorporation of OCN ions achieved an efficiency of 25.32%, an open circuit voltage of 3.021 V, a short circuit current density of 11.48 mA/cm2 and a fill factor of 73.01%.
According to the research team, the introduction of OCN raises the open-circuit voltage from 1.357 V to 1.422 V and results in the highest combination of open-circuit voltage and fill factor for UWBG perovskite solar cells. The cell was also able to retain around 80% of its original efficiency after 300 h.
“This achievement far exceeds the power conversion efficiencies recorded so far by all other perovskite-based triple-junction tandems, as well as single-junction silicon and perovskite solar cells,” says Hou.
The cell was presented in the study “ Triple-junction solar cells with cyanate in ultrawide bandgap perovskites,” published in nature . |
