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NANOSYSTEMS:
PHYSICS, CHEMISTRY, MATHEMATICS Original article
Kozlov S.S., Alexeeva O.V., et al. Nanosystems: Phys. Chem. Math., 2022,13 (3), 314-319.
http://nanojournal.ifmo.ru DOI 10.17586/2220-8054-2022-13-3-314-319
Double perovskite oxides La2NiMnO6 and La2Ni0.8Feo.2MnO6 for inorganic perovskite solar cells
Sergey S. Kozlov1, Olga V. Alexeeva1, Anna B. Nikolskaia1, Oleg I. Shevaleevskiy1'", Denis D. Averkiev2, Polina V. Kozhuhovskaya2'3, Oksana V. Almjasheva2'3'6, Liudmila L. Larina1
1 Solar Photovoltaic Laboratory, Emanuel Institute of Biochemical Physics, Moscow, Russia 2St. Petersburg State Electrotechnical University "LETI", St. Petersburg, Russia 3loffe Physical-Technical Institute, St. Petersburg, Russia
[email protected], [email protected]
Corresponding author: Anna B. Nikolskaia, [email protected]
PAC S 84.60.Jt
Abstract Nanopowders of La2Ni08Fe02MnO6 and La2NiMnO6 double perovskite oxides were synthesized by glycine-nitrate combustion method. The obtained materials were characterized using X-ray diffraction, scanning electron microscopy and optical measurements. Thin nanostructured layers based on the prepared materials were used as light absorbing layers for fabrication of inorganic perovskite solar cells (PSCs). Electron transport layers for the PSCs were prepared using TiO2 and ZrO2 nanostructured layers. The best performance of 3.7 % under AM1.5G illumination was obtained for the PSC structure glass/FTO/ZrO2/La2Ni08Fe02MnO6/ Spiro-MeOTAD/Au.
Keywords nanostructures, double perovskite oxides, perovskite solar cells, solar photovoltaics Acknowledgements This work was supported by the Russian Science Foundation under grant No. 20-6947124.
For citation Kozlov S.S., Alexeeva O.V., Nikolskaia A.B., Shevaleevskiy O.I., Averkiev D.D., Kozhuhovskaya P.V., Almjasheva O.V., Larina L.L. Double perovskite oxides La2NiMnO6 and La2Ni0.8Fe0.2MnO6 for inorganic perovskite solar cells. Nanosystems: Phys. Chem. Math., 2022,13 (3), 314-319.
1. Introduction
Nanostructured materials are widely used for the development of next-generation solar cells since they allow one to fabricate high efficiency and low-cost devices which are promising for mass production photovoltaic technologies [1,2]. In the last decade, numerous studies in the area of solar photovoltaics were focused on the development of perovskite
solar cells (PSCs) [3]. In PSCs an organic-inorganic hybrid material with perovskite-like structure ABX3 (A - CH3NH+, HC(NH2)+, B - Pb2+, Sn2+, X - I-, Br-, Cl-) is used as a light absorbing layer which is deposited on the surface of a nanostructured electron transport layer (ETL) [3-5]. Over a short period of time the power conversion efficiency (PCE) of lab-scale PSCs was increased from 3 - 5 % to 20 - 25 % that is comparable to the performance of conventional crystalline silicon solar cells [6, 7]. Low production costs make PSCs the most promising candidates for the future photovoltaic technologies. At the same time, conventional perovskite materials are not stable and degrade under high humidity conditions, light irradiation and increased temperatures [8,9]. Yet another issue is the presence of the toxic lead cation Pb2+ in the B-site position of conventional hybrid perovskites [10,11]. Therefore, the search for the new environmentally friendly and stable perovskite materials with the improved parameters is an essential task of the modern photovoltaics.
Recently it was reported that the A2B'B''O6 type double perovskite oxides (A is alkaline earth or rare-earth species and B'/B'' are 3d transition species) can be used as a light absorbing photoactive material in PSCs [12,13]. Such inorganic compounds as Ln2NiMnO6, where Ln = La, Eu, Dy or Lu, are characterized by a narrow energy band gap, long carrier lifetime, and good stability under high temperatures and humidity levels [14,15]. The first attempts to fabricate Ln2NiMnO6-based PSCs resulted in poor photovoltaic parameters where the efficiency was less than 1 % [14]. Toimprove the performance, cation doping was used that caused the increase of the transport characteristics of double perovskite oxides [16,17]. A significant increase of the PCE was reached with the introduction of metal atom in the B'-site position that improved the electronic properties of La2NiMnO6 material by increasing the concentration of charge carriers [18].
In this work, nanoparticles of La2Ni1-xFexMnO6 (x = 0,0.2) double perovskite oxides were synthesized by glycine-nitrate combustion method and their structures were investigated using X-ray diffraction (XRD), X-ray fluorescence analysis (XRF), energy dispersive X-ray microanalysis (EDXMA) and scanning electron microscopy (SEM). Using the
© Kozlov S.S., Alexeeva O.V., Nikolskaia A.B., Shevaleevskiy O.I., Averkiev D.D., Kozhuhovskaya P.V., Almjasheva O.V., Larina L.L., 2022
obtained materials for the preparation of the light absorbing layers, we fabricated a series of PSC samples with the following architectures: (1) glass/FTO/TiO2/La2NiMnO6/Spiro- MeOTAD/Au, (2) glass/FTO/TiO2/La2Nio.8Feo.2MnOe/Spiro-MeOTAD/Au, (3) glass/FTO/ZrO2/La2NiMnO6/Spiro-MeOTAD/Au, (4) glass/FTO/ZrO2/La2Ni0.8Fe0.2MnO6/Spiro-MeOTAD/Au and investigated their photovoltaic characteristics.
2. Experiment
2.1. Materials and samples preparation
The La2NiMnO6 (LMNO) and La2Ni0 8Fe0 2MnO6 (LMNO(Fe)) double perovskite oxide nanopowders were synthesized by glycine nitrate combustion method (G/N = 0.55) using corresponding salts according to the procedure described in [19]. The obtained materials were mixed with acetic acid, terpineol, ethyl cellulose and ethanol to obtain homogeneous pastes as specified in [20]. The pastes were sonicated in ultrasonic bath several times and deposited by screen-printing onto FTO conductive glass substrates (Solaronix, 2 x 2 cm) with subsequent annealing at 500 °C for 1 hour to form thin layers for SEM and optical measurements. LMNO and LMNO(Fe)-based homogeneous pastes were then used as precursors for spin coating perovskite light absorbing layers in the process of PSC device fabrication [21].
2.2. Device fabrication
Schematic representation of the PSC architecture is illustrated in Fig. 1. The electron transport layers (ETLs) were fabricated using TiO2 and ZrO2 materials. For this purpose, we used commercially available TiO2 nanoparticles (Degussa-P25) and ZrO2 nanoparticles prepared by dehydration of co-precipitated hydroxides under hydrothermal conditions. The method was described in our previous work [22]. Nanostructured TiO2 and ZrO2 ETLs with 200 nm thickness were deposited on conductive FTO (fluorine-doped tin oxide) glass substrates using spin-coating method at 2000 rpm for 1 min, followed by sintering at 500 °C for 30 min. Next, the light absorbing active layer based on inorganic double perovskite oxide LMNO or LMNO(Fe) and a hole transport layer (HTL) based on Spiro-MeOTAD (Sigma-Aldrich) were successively deposited on the ETL surface. Fabrication of the PSCs was completed by the deposition of Au electrodes with a thickness of 50 nm using thermal evaporation. As a result, we fabricated 4 series of the PSC samples with the following architectures: (1) glass/FTO/TiO2/La2NiMnO6/Spiro-MeOTAD/Au, (2) glass/FTO/TiO2/La2Ni0 8Fe0 2MnO6/Spiro-MeOTAD/Au, (3) glass/FTO/ZrO2/La2NiMnO6/Spiro-MeOTAD/Au, and (4) glass/FTO/ZrO2/ La2Ni0.8Fe0.2MnO6/ Spiro-MeOTAD/Au.
Fig. 1. Schematic representation of the PSC architecture
3. Characterization studies
XRD measurements of LMNO and LMNO(Fe) nanoparticles were provided using DRON-3M X-ray diffractometer with CuKa radiation (A = 1.5405 A) as the X-ray source. The elemental composition of the powders was determined by XRF on a Spectroscan GF-2 X-ray fluorescence spectrometer and EDXMA using Vega 3 Tescan scanning electron microscope with the EDAX energy dispersive analyzer. SEM images of the specially prepared perovskite layers on glass substrates were obtained by Hitachi SU8000 field-emission scanning electron microscope (FE-SEM). The optoelectronic properties of the perovskite layers were characterized using UV-Vis spectrophotometer (Shimadzu UV-3600, Japan) with an ISR-3100 integrating sphere in the wavelength range of 300 - 1400 nm.
Photovoltaic (PV) characteristics of the developed PSCs were measured under standard illumination conditions (AM1.5G, 1000 W/m2) by recording the current-voltage (I-V) characteristics using Keithley 4200-SCS Semiconductor Characterization System (Keithley, USA) and Abet Technologies 10500 solar simulator with Xenon lamp (Abet, USA) as the light source. The PCE (n) values of the PSCs was calculated from the I-V data using the known formula:
n = Jsc ■ Voe ■ FF ioo%, (1)
PIN
where Jsc is the short-circuit current density, VOC is the open-circuit voltage, FF is the fill factor and PIN is the incoming light intensity.
4. Results and discussion
XRD patterns of the LMNO and LMNO(Fe) nanopowders are shown in Fig. 2. The peaks indicate the singlephase perovskite structure and the purity of all samples. The reflexes are recorded for monoclinic, rhombohedral and orthorhombic structures confirming the triple phase structure of double perovskite oxides such as La2NiMnO6 [23]. Table 1 shows the chemical composition and the crystallite size of the synthesized LMNO and LMNO(Fe) nanopowders determined by EDXMA and XRF measurements.
Fig. 2. XRD patterns of La2NiMnO6 andLa2Nio.8Feo.2MnO6 nanopowders
Table 1. Chemical composition and average crystallite size for powders of the double perovskite oxides prepared
Sample Method Chemical composition, mol. % Average crystallite size, nm
La Ni Fe Mn
La2NiFeMnO6 EDXMA 52.5 25.6 0.0 21.9 18 ± 1
La2Nio.8Feo.2MnO6 EDXMA 46.7 25.4 6.6 21.3 20 ± 1
XRF 50.9 22.2 5.7 21.2
SEM images of thin LMNO and LMNO(Fe) layers deposited on glass substrates show porous structure of the layer surfaces (see Fig. 3). It could be seen that LMNO sample exhibits large amount of macropores, while in LMNO(Fe) their number is significantly lower. Besides that, LMNO(Fe) sample possesses more uniform surface and denser morphology which is important for light energy absorbing layer in high efficient PSCs. The decrease in pore size and the enhancement of uniformity of the LMNO(Fe) thin layer in comparison with LMNO sample can be attributed to the partial B'/B'' cation ordering in the crystal structure initiated by the introduction of Fe3+ ions. It is known that La2NiMnO6 is characterized by a disordered structure in which Ni2+, Ni3+, Mn3+, Mn4+ cations randomly occupy B-positions whereas the introduction of Fe3+ ions lead to a predominant content of Ni2+ and Mn4+ ions and to their stricter placement in the lattice structure [24].
The optical measurements have shown that the band gaps for the fabricated thin perovskite layers, calculated from the Tauc plots [25], were 1.18 and 1.28 eV for LMNO and LMNO(Fe), respectively (see Fig. 4). The band gap of the synthesized LMNO(Fe) is close to the Shockley-Queisser limit of 1.34 eV, which provides the maximum power conversion efficiency for the single-junction solar cell [26]. Thus, due to the lower band gap, synthesized LMNO(Fe) double perovskite oxide can absorb larger part of solar radiation in comparison with the halide perovskite CH3NH3PbI3 with a band gap of 1.5 - 1.6 eV, which is used in conventional PSCs [27].
Table 2 summarizes the details on the architectures of the fabricated PSCs and the PV parameters obtained. Inorganic PSCs based on both undoped and Fe3+ doped LNMO layers with TiO2 ETLs exhibited poor PV characteristics (see Table 2). To improve the performance of LNMO-based PSCs, we used the ETLs based on very wide band-gap ZrO2 nanostructured layers with the band gap of ~ 6 eV, which was much larger than that for the TiO2 layer (3.2 eV). Previously we have shown that the charge transport mechanisms at the perovskite/ETL interfaces was entirely different in ZrO2 ETL in comparison with TiO2 ETL [22].
Figure 5 presents schematic energy band diagrams for the developed PSCs based on double perovskite LNMO(Fe) light absorbing layers with TiO2 and ZrO2 ETLs. It could be seen that developed PSCs have different interface electronic
Fig. 3. SEM surface images of LMNO (left) and LMNO(Fe) (right) thin layers
0.75 1.00 1.25 1.50 1.75 2.00 0.75 1.00 1.25 1.50 1.75 2.00
hv, eV hv, eV
Fig. 4. Tauc plots of LMNO (left) and LMNO(Fe) (right) thin layers
Table 2. The architectures of inorganic PSCs and their photovoltaic characteristics under simulated AM 1.5G irradiance
ETL Perovskite light absorbing layer HTL JSC, mA/cm2 Voc , mV FF, a.u. n, %
1 TiO2 La2 NiMnO6 Spiro-MeOTAD 1.2 470 0.4 0.22
2 TiO2 La2 Nio.s Feo.2 MnO6 Spiro-MeOTAD 1.6 495 0.47 0.37
3 ZrO2 La2 NiMnO6 Spiro-MeOTAD 6.5 700 0.49 2.2
4 ZrO2 La2 Nio.s Feo.2 MnO6 Spiro-MeOTAD 8.5 740 0.58 3.7
structures, although both interfaces show the spike conduction band offsets. At the TiO2/LNMO(Fe) interface (Fig. 5a), the conduction band (CB) of the LMNO(Fe) perovskite is located 0.4 eV below the CB of the TiO2 ETL. Such band energy structure reduces the efficient charge transfer across the perovskite/ETL interface to the front FTO electrode and leads to the significant decrease of the device performance. However, valence bands (VBs) structure at the LMNO(Fe)/Spiro-MeOTAD interface found to be favorable for the efficient hole transfer providing the pathways to the Au back electrode. The obtained PV parameters and the PCEs of the developed PSCs with TiO2 ETLs were poor (see Table 2). A slight improvement of the PV parameters was observed for LMNO(Fe)-based PSCs in comparison with LMNO ones, which could be attributed to the higher light absorption ability due the larger Eg value of LMNO(Fe) perovskite material and better morphology of LMNO(Fe) ETL layer.
Incomparably higher conduction band offset is realized at the perovskite/ETL interface when using ZrO2 ETLs (Fig. 5b). Indeed, the CB of the LMNO(Fe) perovskite absorbing layer is located 1.6 eV below the CB position of ZrO2 ETL. Such energy band offset blocks the charge transfer across the perovskite/ETL interface. So, the alternative conductivity mechanism could be considered. In our previous publications, we reported on the successful application of the ZrO2 ETL in the fabrication of inorganic PSCs based on the BiFeO3 perovskite light absorbing layers [22]. It was shown that charge transfer across the BiFeO3/ZrO2 interface was quite efficient regardless the unfavorable interface electronic structure, in which the CB of the BiFeO3 perovskite layer was located 1.1 eV below the CB of the ZrO2 ETL.
Fig. 5. Schematic energy band diagrams for the PSCs based on double perovskite LMNO(Fe) light absorption layers with ZrO2 (a) and TiO2 (b) ETLs
The observed effective electron transfer across perovskite/ZrO2 interface could be described to the hopping conduction through the localized states within the forbidden zone of ZrO2 due to the large concentration of the nanoparticle surface defects [20]. Several publications confirmed that nanostructured layers based on very wide band gap (Eg > 5 eV) materials with negligible density of the electrons in the CB provide the effective transfer due to the large concentration of the surface defects in the forbidden zone. Thus, we have found that the best PCE value of 3.7 % was observed for the PCS device with glass/FTO/ZrO2/ La2Ni0 8Fe0 2MnO6/Spiro-MeOTAD/Au architecture. The new approach for fabrication all inorganic PSCs based on double perovskite oxides with record photovoltaic parameters was developed.
5. Conclusions
Nanopowders of double perovskite oxides La2NiMnO6 and La2Nio.8Fe0.2MnO6 were synthesized using glycine-nitrate combustion method and used to fabricate thin nanostructured light absorbing layers for the inorganic PSCs. XRD, SEM and optical measurements of the prepared layers revealed that the introduction of Fe3+ ions into the crystal structure of La2NiMnO6 material improves the structural properties of the perovskite layer and increases in the optical band gap value from 1.2 to 1.3 eV. For the first time the PSCs based on the LNMO and LNMO(Fe) double perovskite oxides with ZrO2-based ETLs were developed, and their photovoltaic properties were studied. Thus, we have fabricated the series of the PSCs with the following architectures: (1) glass/FTO/TiO2/La2NiMnO6/Spiro-MeOTAD/Au, (2) glass/FTO/TiO2/La2Nio.8Feo.2MnO6/Spiro-MeOTAD/Au, (3) glass/FTO/ZrO2/La2NiMnO6/Spiro-MeOTAD/Au, (4) glass/FTO/ZrO2/ La2Nio.8Feo.2MnO6/Spiro-MeOTAD/Au. The best performance was obtained for the LNMO(Fe)-based PSC with ZrO2 ETL, showing PCE value of 3.7 % under AM1.5G illumination conditions. This value was significantly higher as compared to the PCE values observed for PSCs based on the TiO2 ETLs. It was also shown that very wide-bandgap ETLs provide efficient electron transfer described by hopping transport mechanism.
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Submitted 18 May 2022; accepted 26 May 2022
Information about the authors:
Sergey S. Kozlov - Solar Photovoltaic Laboratory, Emanuel Institute of Biochemical Physics, Russian Academy of Sciences, Kosygin St., 4, Moscow, 119334, Russia; [email protected]
Olga V. Alexeeva - Solar Photovoltaic Laboratory, Emanuel Institute of Biochemical Physics, Russian Academy of Sciences, Kosygin St., 4, Moscow, 119334, Russia; ORCID 0000-0001-8982-3959; [email protected]
Anna B. Nikolskaia - Solar Photovoltaic Laboratory, Emanuel Institute of Biochemical Physics, Russian Academy of Sciences, Kosygin St., 4, Moscow, 119334, Russia; [email protected]
Oleg I. Shevaleevskiy - Solar Photovoltaic Laboratory, Emanuel Institute of Biochemical Physics, Russian Academy of Sciences, Kosygin St., 4, Moscow, 119334, Russia; ORCID 0000-0002-8593-3023; [email protected]
Denis D. Averkiev - St. Petersburg State Electrotechnical University "LETI", Professora Popova St., 5, St. Petersburg, 197376, Russia; [email protected]
Polina V. Kozhuhovskaya - St. Petersburg State Electrotechnical University "LETI", Professora Popova St., 5, St. Petersburg, 197376, Russia; Ioffe Physical-Technical Institute, Russian Academy of Sciences, Politekhnicheskaya St., 26, St. Petersburg, 194021, Russia; [email protected]
Oksana V. Almjasheva - St. Petersburg State Electrotechnical University "LETI", Professora Popova St., 5, St. Petersburg, 197376, Russia; Ioffe Physical-Technical Institute, Russian Academy of Sciences, Politekhnicheskaya St., 26, St. Petersburg, 194021, Russia; ORCID 0000-0002-6132-4178; [email protected]
Liudmila L. Larina - Solar Photovoltaic Laboratory, Emanuel Institute of Biochemical Physics, Russian Academy of Sciences, Kosygin St., 4, Moscow, 119334, Russia; [email protected]
Conflict of interest: the authors declare no conflict of interest.
