Theoretical Design And Photoelectric Property Of New Cells Materials For Solar Cells

Utilizing solar energy to generate electricity through the photovoltaic?PV?effect is a promising technology that can potentially eliminate the use of the limited amount of fossil fuels.The current PV industry is predominately silicon-based with a small share contributed by CdTe and Cu?In,Ga?Se₂?or CIGS?.While the total global installed capacity of PV has reached 300 GW as of 2016,the supply of solar-grade single/polycrystalline silicon has always been a concern when the production is scaled up toward the 30 TW level to make PV a major energy source.A similar material supply issue exists for CdTe and CIGS,as both of these materials contain rare elements.The search for alternative solar-cell materials has thus been a main thrust of renewable energy research worldwide.The emerging perovskite PV materials with the outstanding advantage of high power conversion efficiencies up to 22.7%on par with other conventional commercialized thin-film solar cells,easy fabrication and clean and low cost,are expected to solve the above problems.However,the current perovskite halides suffer from two critical problems toward practical applications,namely,the instability in a humid environment or under solar irradiation and toxicity due to the use of lead.Another perovskite-derived solar materials is the ferroelectric perovskite oxides with low cost,clean and long-term stability targeting at PV applications,but they have oversized bandgap and low carrier conductivity.In addition to the aforementioned light-absorbing layer materials,window layer materials:transparent conductive oxides?TCO?as electrode play an important role in solar cell,requiring transparency to visible light and conductivity for TCO,but most of which suffer from low conductivity.Moreover in the fabrication process of thin film solar cell production,TCO accounts for about 0 to 30%of the whole solar cell raw material costs,thus improving the performance and reducing costs for TCO is crucial to reduce cost of thin-film solar cells.Aiming at solving the problems to solar-cell commercialization faced by solar cell materials including light-absorbing layer materials and window layer materials,the paper will focus on novel solar-cell materials by design and performance optimization by employing quantum chemistry methods combined with theoretical materials design methods.The details are follows:1.Based on the“Valence band chemical modulation:s-p coupling”design concept to achieve good p-type conductivity TCO,we found two family of materials contaning Sn?II?for optoelectronic application,including the p-type TCO.We investigated Sn?II?phosphates:Sn_nP₂O_n+5?n=1,2,3,4,5?and alkaline-earth metal stannates containing Sn?II?:MSn₂O₃?M=Mg,Ca,Sr,Ba?using first-principle calculations combined with global optimization structure prediction methods:1)we focused on known prototype materials Sn_nP₂O_n+5?n=2,3,4,5?and predicted compound SnP₂O₆?n=1?.The calculations indicate they all have large band gaps above 3.2eV to let visible light penetrate and due to the anti-bonding hybridization between the Sn 5s orbitals and the phosphate groups,several compounds show relatively low hole effective masses?²-3m₀?,comparable the electron masses,indicating potential bipolar conductivity.Analysis of structure-property relationships for the metastable structures implies chemical tunability of these properties.The unusual combinations of relatively high band gap,low carrier masses and high chemical stability suggest possible optoelectronic applications of these Sn?II?phosphates,including p-type transparent conductors.2)we presented via first-principles global optimization structure searches study for a hitherto unexplored Sn?II?-based system,MSn₂O₃?M=Mg,Ca,Sr,Ba?.We identify two stable compounds of SrSn₂O₃ and BaSn₂O₃ following the Zintl behaviour.They show distinct electronic properties with band gaps ranging from 1.90?BaSn₂O₃?to3.15?SrSn₂O₃?eV,and hole effective masses ranging from 0.87?BaSn₂O₃?to above6.0?SrSn₂O₃?m₀ indicating a wide tunability of electronic properties.This suggests further exploration of alkaline-earth metal Sn?II?oxides for potential applications requiring good p-type conductivity such as TCO and PV absorbers.2.Science-based inverse-design approach,i.e.,PV functionality-directed theoretical materials selection approach as a filter for initial screening is applied to obtain the single/double halide perovskites with potential superior bulk-material-intrinsic PV performance and the related computational materials design was reviewed with a hope that such this will help identify potential issues as well as enlightening ideas to achieve further computation-driven materials discovery.1)For single halide perovskites:AM^?X₃^?,first-principles calculations are employed to systemically study thermodynamic stability and PV-related properties of hundreds of candidate hybrid perovskites.We have identified in this materials selection process 14 Ge/Sn-based materials with potential PV performance.2)By the strategy of cation-transmutation,convert two divalent Pb²⁺ions in AM^?X₃^?into one monovalent M⁺and one trivalent M³⁺ions,to form a stable inorganic Pb-free double perovskite halides A₂M⁺M³⁺X₆^?for solar cells.Calculations indicate this class of materials have good phase stability and wide range tunable optoelectronic properties.With PV-functionality-directed materials screening,we identify 11 optimal materials as promising candidates to replace Pb-based photovoltaic absorbers in single perovskite solar cells.3)Based on the single/double halide perovskites,the related computational materials design was reviewed with a hope that such this will help identify potential issues as well as enlightening ideas to achieve further computation-driven materials discovery.3.We found the stable configurations with a preferential orientation of organic molecule for various Pb-based compounds and molecular rotation have remarkable tunable effect on the PV performance.Using first-principle calculations combined with global optimization structure prediction,the molecular orientation and rotation effect in the cubic APbI₃?A=[CH₃NH₃]?MA??[CH?NH₂?₂]?FA??[CH₃CH₂NH₃]?EA??were investigated.We predicted the favorite molecular orientation for these compounds,especially the molecular C-N orientation[012]with respect to the crystal axis for MA.Moreover we found that the wide tuning amplitude of band gap,Rashba band splitting and effective mass when the molecule rotates inside the cuboctahedra cavity with the changeable exciton binding energy.4.Our theoretical work successfully explained the fabricated process of high PV performance perovskite thin-film FAPbI3 and proposed the fabricated mechanism,offering useful theoretical explanation and guidance for fabricating high performance perovskite thin-film.Experiment group fabricated a phase pure uniaxial oriented?-FAPbI₃ with large grain with 110?annealing,which leads to an efficiency up to 20.24%.This successful mild temperature crystallization of?-FAPbI₃with uniaxial orientation induced by a spontaneous conversion of high-energy 2D FAMAPbI₃Cl to 3D?-phase FAPb I₃ at room temperature was also investigated by our theoretical studies.We verified the fabrication process and proposed spontaneous2D-3D conversion mechanism,offering useful theoretical explanation and guidance for fabricating high PV performance perovskite thin-film.5.We simulated the alloy BiFexCr1-xO3?0<x<1?and found tunable band gap with various concentration of Fe in favor of improving light absorption efficiency.Based on the cluster expansion technique combined with first-principle calculations,we simulated the structure and electronic properties of the ferromagnetic/antiferromagnetic alloy BiFe_xCr_1-xO₃?0<x<1?.Though studying electronic structure of the endpoint and intermediate compounds,we found the valence band maximum-conduction band minimum have Fe 3d-Cr 3d states or Cr 3d-Fe 3d states which is expected to occur in other alloy.The formation energy of alloy indicates the ferromagnetic alloy is more stable than antiferromagnetic alloy and found two ground state of alloy Bi Fe_0.5Cr_0.5O₃ and BiFe_0.7Cr_0.3O₃,in which Bi Fe_0.5Cr_0.5O₃ with two perovskite structure has been studied.Moreover,the electronic structures of alloy show the wide tuning amplitude of band gap.