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Researchers have developed a thermal regulation strategy to improve the performance of tin-lead inverted perovskite technology for all-perovskite tandem solar cells. An efficiency of 23.4% has been achieved and an efficiency of 27.2% has been contributed to in a tandem cell, while ensuring stability.
A Chinese-Canadian research group has designed an all-perovskite monolithic tandem solar cell using a superior inverted perovskite photovoltaic device based on an absorber made of mixed tin-lead (Sn-Pb) perovskite using a thermal regulation strategy. newly developed.
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 illuminates through the surface of the hole transport layer (HTL).
The scientists explained that their method was to improve the thermal stability and easy oxidation of Sn by incorporating carboranes into the perovskite material. These compounds, also known as dicarba-closo-dodecaboranes, are electron-delocalized groups formed by boron, carbon and hydrogen atoms with heat transfer capacity.
“Carboranes are electronically delocalized carbon-boron molecules with significant overlap between the atomic orbitals of neighboring atoms, allowing electrons to move freely and spread over a broader region within the materials,” they stated. “The characteristic of electron delocalization allows them to improve thermal conductivity and efficient carrier transport.”
The group selected a type of carborane known as orthocarborane (o-CB, C2B10H12) and said it has “exceptional” heat transfer capacity and chemical stability. It was placed in the cell to avoid direct contact between the perovskite and the PEDOT:PSS (HTL) layer to prevent its degradation at high temperatures.
The top solar cell was constructed with an indium tin oxide (ITO) substrate, a PEDOT:PSS-based hole transport layer (HTL), the perovskite absorber, an electron transport layer (ETL) based on buckminsterfullerene (C60), a tin oxide (SnO2) buffer layer and a silver (Ag) metal contact.
Using density functional theory (DFT) calculations, the academics found that orthocarborane and perovskite could stably combine, and subsequent ultraviolet photoelectron spectroscopy (UPS) measurements confirmed the enhancement of the interfacial energy level of the absorber. .
“The valence band maximum of a perovskite film shifted from -5.42 to -5.31 eV upon treatment with orthocarborane, making its band shift with the highest-occupying molecular orbital of PEDOT:PSS smaller and reducing interfacial recombination,” they explained.
A champion solar cell built with this configuration achieved a power conversion efficiency of 23.4%, an open circuit voltage of 0.877 V, a short circuit current density of 32.19 mA cm2, and a fill factor of 82. 9%. The device also retained 90% of its initial efficiency after 1,000 h. In comparison, a cell without carborane treatment retained only 62% of its original efficiency after 400 h.
The cell was then integrated as a top device into a monolithically integrated all-perovskite solar cell based on Sn-Pb perovskite bottom cells. The tandem cell achieved an efficiency of 27.2%, an open circuit voltage of 2.16 V, a short circuit current density of 15.6 mA/cm2 and a fill factor of 81%.
“We further tested the stability of encapsulated tandem solar cells under simulated illumination from a sun at MPP,” the group said. “The pristine tandem retained 87% of its initial efficiency after 704 hours of continuous operation.”
The new solar cell concept was presented in the recently published study “ Sustainable thermal regulation improves stability and efficiency in all-perovskite tandem solar cells .” in Scientific Reports . The research team consisted of academics from the University of Toronto (Canada) and Qingdao University of Science and Technology (China).
Another research group at the University of Toronto has just introduced an all-perovskite triple junction solar cell with a 25.1% efficiency that reportedly improves the homogenization of the perovskite halide film. |
