O.E. Glukhova – Dr.Sc.(Phys.-Math.), Professor, Head of the Department of Radiotechnique and Electrodynamics,  Saratov State University named after N.G. Chernyshevsky 

E-mail: GlukhovaOE@info.sgu.ru

D.A. Kolosov – Post-graduate Student, 

Department of Radiotechnique and Electrodynamics, Saratov State University named after N.G. Chernyshevsky  E-mail: demkol.93@mail.ru

M.M. Slepchenkov – Ph.D.(Phys.-Math.), Associate Professor, 

Department of Radiotechnique and Electrodynamics, Saratov State University named after N.G. Chernyshevsky  E-mail: slepchenkovm@mail.ru

This paper is devoted to a theoretical study of the optical conductivity and photovoltaic properties of three allotropic forms of borophene – triangulated, β12 and χ3, as well as an assessment of the prospects for the use of borophene for photovoltaic applications. The construction of atomistic models of 2D unit cells for triangulated, β12 and χ3 borophene was carried out using the SCC DFTB method in the DFTB+ software package. In our calculations, the Brillouin zone was divided using the Monkhorst-Pack scheme. To calculate the optical conductivity tensor, the Kubo–Greenwood formula was used. New physical effects were revealed based on the results of a study. For the first time it was found that a triangulated borophene may be promising in highly efficient photodetectors of ultraviolet (UV) radiation, since this material is absent outside the UV range. The two other allotropic borophene modifications are characterized by the presence of pronounced absorption peaks in the visible spectral range. All types of borophene are very different from graphene. Graphene has one pronounced peak in the UV region and in the visible region. The conductivity of graphene is characterized by one conduction quantum. Analysis of the calculated maximum values of the photocurrent showed that 2D material based on χ3 borophene сan be extremely promising as a sensitive element of solar cells. This 2D material showed the highest value of the integral photocurrent for the visible emission spectrum of 0.892 мА·см2 for AM0 solar spectrum and 0.742 мА·см2 for AM1.5G solar spectrum. In comparison with graphene, borophen shows a larger value of the integral value of the photocurrent of the visible range for the case of the absence of the atmosphere (AM0 spectrum) by 31.73%, and for the case of the presence of the atmosphere (AM1.5G spectrum) by 32.73%.

1. Mannix A.J., Zhou X.F., Kiraly B. et al. Synthesis of borophenes: anisotropic, two-dimensional boron polymorph. Science. 2015. V. 350. № 6267. P. 1513−1516. DOI: 10.1126/science.aad1080.
2. Feng B., Zhang J., Zhong Q., et al. Experimental realization of two-dimensional boron sheets. Nature Chemistry. 2016. V. 8.
   1. 563−568. DOI: 10.1038/nchem.2491.
3. Novoselov K., Geim A., Morozov S., et al. Electric field effect in atomically thin carbon films. Science. 2004. V. 306. P. 666−669. DOI: 10.1126/science.1102896.
4. Kim K., Hsu A., Jia X., et al. Synthesis of monolayer hexagonal boron nitride on Cu foil using chemical vapor deposition. Nano Letters. 2012. V. 12. P. 161−166. DOI: 10.1021/nl203249a.
5. Radisavljevic B., Radenovic A., Brivio S. et al. Single-layer MoS2 transistors. Nature Nanotechnology. 2011. V. 6. P. 147−150. DOI: 10.1038/nnano.2010.279.
6. Tongay S., Zhou J., Ataca C., et al. Thermally driven crossover from indirect toward direct bandgap in 2D semiconductors: MoSe2 versus MoS2. Nano Letters. 2012. V. 12. P. 5576−5580. DOI: 10.1021/nl302584w.
7. Sha Z.D., Pei Q.X., Zhou K. et al. Temperature and strain-rate dependent mechanical properties of single-layer borophene. Extreme Mechanics Letters. 2018. V. 19. P. 39−45. DOI: 10.1016/j.eml.2017.12.008.
8. Zhong H., Huang K., Yu G. et al. Electronic and mechanical properties of few-layer borophene. Physical Review B. 2018. V. 98.
   1. 31−40. DOI: 10.1103/ PhysRevB.98.054104.
9. Gao M., Li Q.Z., Yan X.W., et al. Prediction of phonon-mediated superconductivity in borophene. Physics Review B. 2017. V. 95.
   1. 76−86. DOI: 10.1103/ PhysRevB.95.024505.
10. Penev E.S., Kutana A., Yakobson B.I. Can two-dimensional boron superconduct. Nano Letters. 2016. V. 16. P. 2522−2526. DOI: doi.org/10.1021/acs.nanolett.6b00070.
11. Lian C., Hu S., Zhang J. et al. Exotic surface plasmons in monolayer metal borophene. Eprint arXiv. 2018. 1803.01604.
12. Nair R.R., Blake P., Grigorenko A.N. et al. Fine Structure Constant Defines Visual Transparency of Graphene. Science. 2008. V. 320. P. 1308. DOI: 10.1126/ science.1156965.
13. Bernardi M., Palummo M., Grossman J. Extraordinary Sunlight Absorption and One Nanometer Thick Photovoltaics Using TwoDimensional Monolayer Materials. Nano Letters. 2013. V. 13. P. 3664−3670. DOI: doi.org/10.1021/nl401544y.
14. Palik E.D. Handbook of Optical Constants of Solids. New York: Academic Press. 1998.
15. URL = https://www.dftb.org/ (18.03.2018).
16. Sorkin V., Zhang Y.W. Mechanical properties of pristine and defective carbon-phosphide monolayers: a density functional tight-binding study. Nanotechnology. 2018. V. 29. P. 300−317. DOI: 10.1088/1361-6528/aad9e8.
17. Selli D., Fazio G., Seifert G. et al. Water multilayers on TiO2 (101) anatase surface: Assessment of a DFTB-based method. J. Chem. Theory Comput. 2017. V. 7. P. 3862−387. DOI: 10.1021/acs.jctc.7b00479.
18. Monkhorst H.J., Pack J.D. Special points for Brillouin-zone integrations. Phys. Rev. B. 1976. V. 13. P. 5188−5192. DOI: doi.org/10.1103/PhysRevB.13.5188.
19. Calderín L., Karasiev V.V., Trickey S.B. Kubo-Greenwood electrical conductivity formulation and implementation for projector augmented wave datasets. Computer Physics Communications. 2017. V. 221. P. 118−142. DOI: 10.1016/j.cpc.2017.08.008.
20. Stauber T., Peres N.M.R., Geim A.K. Optical conductivity of graphene in the visible region of the spectrum. Phys. Rev. B. 2008. V. 78. P. 62−69. DOI: 10.1103/ PhysRevB.78.085432.
21. Glukhova O.E., Nefedov I.S., Shalin A.S., Slepchenkov M.M. New 2D graphene hybrid composites as an effective base element of optical nanodevices. Beilstein J. Nanotechnol. 2018. V. 9. P. 1321−1327. DOI: 10.3762/bjnano.9.125.
22. Maurizia P., Bernardi M., Grossman J.C. Exciton Radiative Lifetimes in Two-Dimensional Transition Metal Dichalcogenides. Nano Lett. 2015. V. 5. P. 2794−2800. DOI: doi.org/10.1021/nl503799t.
23. URL = http://rredc.nrel.gov (03.04.2019).