Theoretical Study Of Light-absorbing Materials In Dye Sensitized And Organic Solar Cells

With the rapid development of science and technology,human demand for energy is increasingly growing.The overuse of traditional energy,which leads to the energy crisis,makes people develop novel energy.Photovoltaic power generation,a process of directly converting photo electricity through solar cells is one of the most important ways to utilize solar energy.The development and research of efficient solar cell materials have increasingly become a research hotspot in the scientific research field.Dye-Sensitized Solar Cells(DSSCs)and Organic Solar Cells(OSCs)are the two promising photovoltaic devices due to low-costing,facile fabrication,and low pollution.Studies show that the properties of dye-sensitizers and non-fullerene acceptors(NFAs)have an important influence on photoelectric conversion efficiency(PCE)of solar cells.To improve the performance of the two kinds of solar cells,density functional theory(DFT)and time-dependent density functional theory(TD-DFT)were used to explore the influence of the structure of C275-Series dyes and Y-Series NFAs on photoelectric performance.Based on the exploration,using experimentally synthesized C275 and Y6with excellent performance as reference molecules,CD1-CD5,D1-D5,and T1-T3 were designed through structural modifications.Then their photoelectric properties were systematically studied.Compared with C275 and Y6,the highest PCE of designed dyes and NFAs increased by approximately 56%and 33%,respectively.We hope our investigation can provide theoretical guidance for the development of DSSCs and OSCs.This paper mainly includes the following three aspects of work:(1)To explore the influence of the structures of dye-sensitizers on the performance of DSSCs,we design eleven dyes CS1-CS11 by using three strong electron-donating groups(D1-D3)and eight electron acceptors(A4-A11)based on C275.The ground state structures,electronic structures,and absorption spectra of CS1-CS11 are simulated and analyzed by DFT and TD-DFT methods.The effects of different donor and acceptor structures of the dye-sensitizers on the performance of DSSCs are discussed theoretically.The results show that the D1 and A4-A8 with narrower HOMO-LUMO gaps and stronger light absorption characteristics efficiently improve the PCE.Thereby,D1 and A4-A8 were selected as high-performance organic dye electron donor and acceptor candidates,respectively.On the basis of above results,we designed five potential dye-sensitizers CD1-CD5 and calculated the photoelectric properties by using DFT and TD-DFT methods.Compared with C275,the designed dyes exhibit enhanced light-harvesting abilities in which the absorption spectra extend to the near-infrared region with the improvement of?119 nm redshift maximum absorption wavelengths and wider light-harvesting efficiency(LHE)curves,ascribed to their more conjugated structures and narrower bandgaps.Mainly distributed by the obvious enhancement of?42%for the theoretical short current densities(J_sc^Theor.),the open-circuit voltage also increases by?8%,the power conversion efficiency(PCE)of the designed dyes increases by more than 54%compared to C275.Consequently,dyes CD1-CD5 have the potentials to be promising candidates with an overall efficiency beyond 18.8%.(2)Using DFT/TD-DFT methods and Marcus transfer theory,NFAs including Y6,Y10,and Y11 and electron donors comprising PM6,J11,are taken as a representative system to theoretically explore the influence of diverse electron-withdrawing groups as terminal groups(A)and fused-rings as the electron-deficient core(A?)of NFAs on the performance of OSCs devices.The results show that the introduction of terminal groups(A)and electron deficient-core(A?)with strong electron-withdrawing ability into NFAs,reduces the molecular hardness()and electron recombination energy(_e),extends the first excited-state lifetime(),increases the electron transfer rate(_e)and electron mobility(_e),the₀)/₀)value of Y11 is about 3 times than that of Y10.The results of the D/A complexes indicate that introducing the strong electron-withdrawing groups into the terminal and core groups of NFAs improves the optical absorption properties of the complexes,reduces the charge recombination rate(_CR),and enhances charge separation rate(_CS),thus leads to higher PCE.More importantly,the designed D/A interfaces have a superior_CS/_CR rate than the experimental interfaces.(3)On the basis of the second part,eight NFAs D1-D5 and T1-T3 were designed by modifying the structure of electron donors and terminal groups based on Y6.The photoelectric properties of the designed molecules are investigated by using DFT/TD-DFT methods and Marcus charge transfer theory.The results show that D1-D5 and T1-T3 have a lower hardness and a narrower HOMO-LUMO gap compared with Y6.Meanwhile,the designed molecules have a wider and stronger light absorption range with?101 nm redshift maximum absorption wavelengths and 6%-46%increment of oscillator strength.D1-D5 and T1-T3 have faster intramolecular charge transfer rate/mobility,in which the mobility of D1 is about 10³ times that of Y6 in the charge transfer process.The data of PM6/NFAs interfaces show that the designed molecular interfaces have a significantly faster charge separation rate.In general,compared with Y6,the designed molecules have better photoelectric properties because of the fusion of electron-donating units and strong electron-withdrawing terminal groups in NFAs,resulting in a more conjugated structure and narrower HOMO-LUMO gaps.More importantly,the PCE of designed NFAs are higher than Y6(15.7%)by the improved Scharber model.Among then,the PCE of D5 is up to 20%.Our study manifests that D1-D5 and T1-T3 are potential high-performance NFAs materials.