Technische Universität Dresden researchers have designed new solar cells based on phase heterojunctions. They used two perovskite polymorphs to build a novel PV device with an efficiency of 20.1% and a fill factor of 84.17%.
“We hope that this novel concept combined with a simple fabrication route for phase heterojunctions will be applicable also to a variety of material systems in a range of electronic and optoelectronic devices,” said researcher Yana Vaynzof.
Vaynzof noted that the novelty of the new approach lies in the realization of a junction based on the combination of two components with different optoelectronic properties. The scientists chose the β- and γ-phases of a perovskite material known as CsPbI3 for the two polymorphs.
“Our choice of the β-CsPbI3 and γ-CsPbI3 phases for the demonstration of the PHJ concept was motivated by their relatively low-temperature processing, unlike the α-CsPbI3 that requires annealing at less than 300 C,” they explained. “Considering that solution processing of all polymorphs of CsPbI3 requires the use of the same type of polar solvent38, we utilized a hybrid deposition approach that combines both solution processing and thermal evaporation.”
The team used scanning electron microscopy (SEM) to characterize the microstructure of the deposited layers and their surface. It found that the solution-processed β-CsPbI3 shows uniform, large grain size with an average diameter of around 300 nm. They also found that the energy bandgap of the γ- and β-CsPbI3 was 1.74 eV and 1.69 eV, respectively.
“Their two slightly different bandgaps result in the absorbance spectra of the PHJ samples displaying features originating from both phases,” they said, adding that their optimal thickness is between 500 nm and 370 nm.
The researchers said the cell configuration offers an increase in all photovoltaic parameters. It has a power conversion efficiency of 20.17% and a maximum fill factor of 84.17%.
“Advanced spectroscopic analysis revealed that this improvement in performance is associated with increased light absorption and the formation of an advantageous energetic alignment between the two phases,” said Vaynzof.
The academics presented the new cell technology in “Perovskite phase heterojunction solar cells,” which was recently published in Nature Energy.
“The approach demonstrated here offers new possibilities for the development of photovoltaic devices based on polymorphic materials,” they said.
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