Theoretical Screening And Study Of Ternary Six-fold Photovoltaic Semiconductors

Solar cell is a kind of device to convert solar energy into electrical energy,which is an effective method for solar energy conversion and utilization.For the last several years,people have been working on the subject to find earth-abundant,environmentfriendly and highly efficient semiconductor materials as absorbing layers for solar cells to ultimately realize large-scale applications of solar cells.ABS2,a family of six-fold ternary sulfides proposed as stable earth-abundant,environment-friendly semiconductors for solar cells,has attracted a great amount of attention in the last few years.Several ABS2 compounds are reported to have thermodynamic stabilities,suitable band gaps and band structures,and high light absorption coefficients in the visible region,meet the critical requirements of light-absorbing materials for solar cells.Thus,the high-throughput calculations and theoretical screening of ternary six-fold sulfides and two further theoretical studies of the typical prototype materials are carried out in this paper using the first-principles calculations.The three parts of work in this dissertation are illustrated as follows:(1)High-throughput calculations and screening of ternary six-fold sulfides ABS2 for photovoltaic semiconductors.Based on the first-principles calculations of 216 compounds,screening of the thermodynamic stability,band gap width,light absorption,and effective masses of charge carriers,we proposed 18 semiconductors with high photovoltaic potential for solar cell light absorbers,including LiSbS2(R3M)、LiBiS2(R3M)、NaSbS2(R3M)、NaBiS2(R3M)、KSbS2(R3M)、RbSbS2(R3M)、AgBiS2(R3M)、NaSbS2(141/amd)、NaBiS2(Pnma)、NaSbS2(C2/c)、NaBiS2(C2/c)、LiBiS2(C2/m)、NaSbS2(C2/m)、NaBiS2(C2/m)、KSbS2(C2/m)、KBiS2(C2/m)、RbSbS2(C2/m)、RbBiS2(C2/m).(2)According to our high-throuput study above,LiBiS2(R3M)is proposed as a highly potential light absorber for solar cells.To further show its potential application in solar cells,we have carried out a further theoretical study of LiBiS 2.The calculation results show that LiBiS 2 is a thermodynamically stable semiconductor material with a direct bandgap of 1.49 eV,and its light absorption coefficient in the visible light region exceeds 1 × 105 cm-1,which meets the requirements for photovoltaic light absorbers.In addition,LiBiS 2 is capable of forming shallow p-type intrinsic defects dominated by VLi under S-rich growth conditions and deep n-type intrinsic defects dominated by Vs under S-poor conditions.The appropriate thermodynamic stability,band structure,light absorption and defect properties of LiBiS2 indicate that LiBiS2 is a potential highperformance photovoltaic semiconductor.(3)AgBiS2 is a synthetic six-fold semiconductor with visible-light response.The arrangement of Ag and Bi cations can alter to cause the band gap reduction in experiments.Inspired by this,we propose to design a stable infrared photoelectric semiconductor AgBiS2 by cation disorder.Adopting the quasi-random structures(SQS)combined with the first-principles calculations,the band gaps of ordered and disordered AgBiS2 are estimated.The calculated results show that the optical band gap of AgBiS2 can be tuned continuously in the range of 0.33～1.46 eV,achieving light response in the full near-infared and part of mid-infared region.The phase transition between fully ordered and fully disordered AgBiS 2 requires only 0.11 eV/f.u..Therefore,we proposed that the band gap,i.e.the light-response region,of AgBiS 2 can be precisely adjusted by controlling the synthetic temperature.