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A team of German researchers has studied the optical properties of perovskite/perovskite/silicon triple junction cells and found that these devices can have a potential practical efficiency of 44.3% assuming idealized electrical parameters. These cells could also reach a fill factor of 90.1%.
A group of German researchers has developed a comprehensive optoelectric simulation model for triple-junction solar cells based on perovskite, perovskite, and crystalline silicon subcells, respectively.
The model aims to define an efficiency roadmap to improve the optical properties of these solar cells within realistic boundary conditions. “The roadmap includes the adaptation of the thicknesses of the perovskite absorbers, the modification of the bandgaps, the use of a fully textured cell and the optimization of the thicknesses of the intermediate layers between the absorbers,” the scientists explain. “We calculate the respective photocurrent of each step and compare it with the theoretical limit.”
For its modeling, the academics chose the Sentaurus TCAD, which is a multidimensional simulator capable of simulating the electrical, thermal and optical characteristics of silicon-based devices. It is also used to simulate the optoelectronic characteristics of semiconductor devices, such as image sensors and photovoltaic cells.
“This tool has already demonstrated its ability to accurately describe the optical properties of perovskite tandem solar cells,” they say, referring to previous similar research they carried out on perovskite-silicon tandem cells. In this work, they concluded that the practical power conversion efficiency potential of perovskite-silicon tandem devices can reach up to 39.5%.
In their most recent work, the researchers initially assumed that the triple junction cell would be based on a lower silicon heterojunction cell with an indium tin oxide (ITO) layer and a silver (Ag) metal contact. ), an intermediate perovskite cell with an energetic bandgap of 1.57 eV and a higher perovskite cell with a bandgap of 1.84 eV.
In the optimization process, their efforts were directed at increasing the photocurrent of all three cells. Initially they varied the thicknesses of the three absorbers and then adjusted the bandgaps of the perovskites. Additionally, they applied a textured front face to mitigate reflection losses and used thinner interlayers. “Tailoring the thicknesses of perovskite absorbers is quite simple, but has the potential to achieve current equalization between the top and middle cell,” the group stressed. “This way, the current can be significantly improved.”
The scientists also calibrated the thickness of the magnesium fluoride (MgF2)-based anti-reflective coating by reducing its thickness from 130 nm to 90 nm. They also initially increased the thickness of the middle cell perovskite absorber, which they said reduces photon absorption in the silicon subcell, but offers improved absorption in the top and middle devices, thus increasing the photocurrent at the silicon level. the triple junction cell.
The simulation showed that the best cell configuration can potentially achieve a power conversion efficiency of 44.3%, an open circuit voltage of 3480 mV, a short circuit density of 14.1 mA cm-2 and a fill factor of 90.1%. This was achieved with a middle perovskite cell with an energetic bandgap of 1.46 eV and a top perovskite cell with a bandgap of 1.97 eV.
“On the other hand, we showed that the bandgap range of the top cell could be chosen between 1.8 and 2.0 eV, depending on the thickness of the top cell, which varies between 200 and 800 nm, respectively, for each of which there is a bandgap/thickness tuple that allows global adaptation of the current to be achieved,” the scientists stressed. “However, we have drawn attention to the desirability of choosing thicker perovskite layers with higher bandgap to release the full open-circuit voltage potential of the upper cell.”
The results are published in the article “ Optoelectrical Modeling of Perovskite/Perovskite/Silicon Triple-Junction Solar Cells: Toward the Practical Efficiency Potential ” , recently published in RRL Solar . The research team consisted of scientists from the University of Freiburg and the Fraunhofer Institute for Solar Energy Systems (Fraunhofer ISE). |
