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An international team of researchers constructed the triple junction device with a dual surface and interface passivation technique to promote halide homogeneity at the interface between the perovskite absorber and the hole transport layer. The 0.049 cm2 cell achieved a remarkable open circuit voltage of 3.33 V and was also able to retain 80% of its initial efficiency after 200 h of continuous monitoring of the maximum power point.
An international group of researchers led by the University of Toronto, Canada, has developed an all-perovskite triple junction solar cell that reportedly features improved homogenization of the perovskite halide film.
The scientists explained that their new strategy to improve film quality and cell efficiency was intended to overcome a problem typical of all-perovskite triple-junction monolithic photovoltaic devices, which typically exhibit higher band shift with metal transport layers. charge and defect density in broadband perovskite absorbers. This makes its efficiency lower than that of its double- and single-junction counterparts.
“We attempted to improve the homogeneity of bulk and interfacial halides in a bromine-rich 2 eV broadband perovskite absorber to reduce energy losses,” corresponding author of the research, Edward Sargent, told pv magazine .
Their method consisted of a dual surface and interface passivation technique aimed at promoting halide homogeneity at the interface between the perovskite absorber and the hole transport layer (HTL). It involves the introduction of a diammonium halide salt known as propane-1,3-diammonium iodide (PDA) during film formation.
The cell had a surface area of ??0.049 cm2 and an inverted configuration. 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.
The device was designed with a glass substrate, a transparent hydrogen-doped indium oxide (IOH) back contact, a hole transport layer (HTL) made of nickel(II) oxide (NiOx), and phosphonic acid called carbazole. methyl-substituted (Me-4PACz), a wide bandgap perovskite absorber, a spacer based on phenyl-C61-butyric acid methyl ester (PCBM) and polyethyleneimine (PEI), a tin oxide (SnOx) buffer layer , an indium tin oxide (ITO) layer, another HTL based on NiOx and Me-4PAC, a medium bandgap perovskite absorber, a buckminsterfullerene (C60) electron transport layer (ETL), another buffer layer of SnOx, a gold (Au) metal contact, another HTL based on the PEDOT:PSS polymer, a narrow band gap perovskite absorber, an ETL of C60, another SnOx buffer layer and a silver (Ag) metal contact .
The energetic bandgap of the three absorbers was 1.97 eV, 1.61 eV, and 1.25 eV, respectively.
According to the researchers, PDA effectively interacted with perovskite precursors and slowed down the formation of perovskite films during spin coating, resulting in delayed crystallization of the films. “Therefore, we speculate that PDA allows controlled growth between halide species and facilitates homogeneous transformation to intermixed perovskite phases,” they explained. “PDA cations bind strongly to the interfaces of adjacent perovskite fragments, allowing more relaxation time for the exchange of different halide ions and thus the formation of uniform mixed halide perovskite phases.”
Tested under standard lighting conditions, the triple junction device showed a power conversion efficiency of 25.1%, an open circuit voltage of 3.33 V, a short circuit current of 9.7 mA cm2, and a filling of 0.78. The device was also able to retain 80% of its initial efficiency after 200 h of continuous maximum power point tracking (MPPT).
For its part, the National Renewable Energy Laboratory (NREL) of the US Department of Energy has certified an efficiency of 23.87% for the device using the maximum power asymptotic sweep protocol.
“We have observed that, although diammonium salt does not suppress light-induced halide segregation, the bandgap cell maintains high operational stability under prolonged illumination, beyond the stability of the approximately 2 eV cells from which It is documented in the literature,” the scientists say. |
