Theoretical Searching Intermediate Band Solar Cell Absorber Based On Cheap And Nontoxic Semiconductor

With the increasing of environment pollution caused by fossil fuel combustion and numerous global energies demanding in the world,finding new energy to replace fossil fuels has been paid global attention.Solar energy is a renewable energy,and solar cell has been widely studied since it can convert solar energy to electric energy directly.Recently,the development of solar cells has grown rapidly,however most of them still suffered from some problems like high production cost,composition from toxic elements,conversion efficiency limited by Shockley-Queisser limit.Therefore,finding a low-cost,nontoxic and high efficiency solar cell absorber will provide driving force for the advancement of solar cells.The principle of intermediate band solar cell(IBSC)is introducing an intermediate band(IB)into a host semiconductor through element doping with high concentrations.Owing to the presence of IB,three photons absorption can be realized and the theoretical efficiency of IBSC can exceed the maximum efficiency of single junction solar cell.The specific studies are as follows:1.Based on first-principle calculations,we have studied the electronic structure and optical absorption coefficients of pure Sn S₂and Sb doping Sn S₂,and the defect formation energies of Sb doping at Sn site(Sb _Sn),S site(Sb _S)and interstitial site(Sb_i),respectively.The calculation results indicated that a half-filled and delocalized IB presented in the band gap of Sn S₂after Sb doping at Sn site,and the IB originates from the anti-bonding states of Sb-s and S-p states.Due to the existence of IB,the optical absorption coefficient of the doped sample is strengthened compared with that of pure Sn S₂,and the optical absorption range in the visible light is enlarged.Moreover,according to the calculation of defect formation energy,Sb _Snhas lower formation energy comparing with Sb _Sand Sb_i,indicating that large doping concentration of Sb _Sncan be achieved.Therefore,Sb doped Sn S₂is suggested as cheap and non-toxic IBSC absorber.2.Through the first-principle calculations,we have calculated the electronic structure,optical absorption coefficient and defect formation energy of P doped Cu₂Si S₃,respectively.The electronic structure of the P doped Cu₂Si S₃indicated that a half-filled and delocalized IB is introduced in the host Cu₂Si S₃after P doping at Si site,and the IB derives from the anti-bonding states between S-p and P-s and between S-p and P-p states.After the comparison on the optical absorption coefficients of pure Cu₂Si S₃and the doped samples,we found that the optical absorption coefficient in the visible light region has been enhanced after P doping and increased with the doping concentration increasing.Meanwhile,through the calculation of defect formation energy,we found that P doping at Si site is easier to be achieved in a large doping concentration.Therefore,P doped Cu₂Si S₃can be suggested as an IBSC absorber from cheap and non-toxic elements.3.Based on the first-principle calculations,we found that the pure?-Sr Zr S₃has small effective masses from its electronic structure,which is beneficial to the carrier separation.A half-filled and delocalized IB is introduced in?-Sr Zr S₃after Sb doping at Zr site,and the optical absorption coefficients of Sb doped samples increase in the visible light region with the doping concentration increasing.Calculations of defect formation energy indicate that high concentration doping is easier to be achieved for Sb doing at Zr site other than Sb doping at Sr site or S site.Therefore,Sb doped?-Sr Zr S₃can be suggested as an ideal cheap,non-toxic IBSC absorber.