Very interesting work. I have a question, I hope it is related... Can you observe dipole formation at the interface with this type of calculations? I understand that an enhancement of electron extraction can occur after the formation of this dipoles. Thank you
We can observe dipole formation, and the differences between different kinds of interfaces, but the quantification of the dipole moment is not unique. In the poster 4 you can see a study of another interface. We have also obtained the Bader charges, which are not in that poster, but can be seen in full article at https://arxiv.org/abs/2006.15161
From the Bader charges one can compute a dipole moment. One can also obtain it directly from the total (nuclear+electronic) charge density, and the result is different. We have chosen not to speak about dipole moments. Basically, the problem is that the electric dipole moment depends upon the origin of the coordinate system, unless the total charge is zero. Hence, the dipole molecule is well defined for a neutral molecule, but not for a charged one, e.g., the CH3NH3 cation. For an interface, to obtain dipole moments that are independent of the coordinate origin, one shoul define a volume enclosing the interface that has charge 0, but these volumes are arbitrary. Some papers quantify the so called interface dipole, which is a term that contributes to the band energy difference across the interface. This is given with respect to a specific interface or with respect to the band energies obtained aligning the vacuum levels of the surfaces of both materials separated, but this is reference is also arbitrary, as a material like CH3NH3PbI3 has several types of surfaces. The concept may still be useful as a qualitative guide for interface design. In general, we believe that charge extraction is favoured by the alignment of the band edges at both sides of the interfaces. This is a well defined quantity. However, it is not that simple. To have more specific prediction one needs to model the full device at the mesocopic scale, with a softwares like SCAPS.
Eduardo, thank you for the interesting explanation on the topic, I have a better idea now!
We have studied experimentally two different interfaces in PSCs: mesoporous TiO2/perovskite and compact TiO2/perovskite. We observed a reproducible increment in the open-circuit potential of ~0.05 V. This is accompained by an increment in the lifetime of the devices. We compared with other ETLs and found that the degradation dynamics are related to recollection of the charges. Please have a look at the full article if you find it interesting: https://www.sciencedirect.com/science/article/abs/pii/S0038092X20302796
On the other hand, the preparation of polymeric HTL is also of interest and could be very interesting to have a theoretical study to complement the selection of the best materials. This is my e-mail: alejandra.castro@cinvestav.mx. Please visit my poster: #90.
Comments
I have a question, I hope it is related... Can you observe dipole formation at the interface with this type of calculations? I understand that an enhancement of electron extraction can occur after the formation of this dipoles. Thank you
We can observe dipole formation, and the differences between different kinds of interfaces, but the quantification of the dipole moment is not unique. In the poster 4 you can see a study of another interface. We have also obtained the Bader charges, which are not in that poster, but can be seen in full article at https://arxiv.org/abs/2006.15161
From the Bader charges one can compute a dipole moment. One can also obtain it directly from the total (nuclear+electronic) charge density, and the result is different. We have chosen not to speak about dipole moments. Basically, the problem is that the electric dipole moment depends upon the origin of the coordinate system, unless the total charge is zero. Hence, the dipole molecule is well defined for a neutral molecule, but not for a charged one, e.g., the CH3NH3 cation. For an interface, to obtain dipole moments that are independent of the coordinate origin, one shoul define a volume enclosing the interface that has charge 0, but these volumes are arbitrary. Some papers quantify the so called interface dipole, which is a term that contributes to the band energy difference across the interface. This is given with respect to a specific interface or with respect to the band energies obtained aligning the vacuum levels of the surfaces of both materials separated, but this is reference is also arbitrary, as a material like CH3NH3PbI3 has several types of surfaces. The concept may still be useful as a qualitative guide for interface design. In general, we believe that charge extraction is favoured by the alignment of the band edges at both sides of the interfaces. This is a well defined quantity. However, it is not that simple. To have more specific prediction one needs to model the full device at the mesocopic scale, with a softwares like SCAPS.
We have studied experimentally two different interfaces in PSCs: mesoporous TiO2/perovskite and compact TiO2/perovskite. We observed a reproducible increment in the open-circuit potential of ~0.05 V. This is accompained by an increment in the lifetime of the devices. We compared with other ETLs and found that the degradation dynamics are related to recollection of the charges. Please have a look at the full article if you find it interesting: https://www.sciencedirect.com/science/article/abs/pii/S0038092X20302796
On the other hand, the preparation of polymeric HTL is also of interest and could be very interesting to have a theoretical study to complement the selection of the best materials. This is my e-mail: alejandra.castro@cinvestav.mx. Please visit my poster: #90.