Theoretical Study On Photodynamics Of Three Kinds Of Solar Cells Based On Fullerene,Non-fullerene Acceptors And Inorganic Perovskite

Organic solar cells,perovskite solar cells and two-dimensional van der Waals heterojunction solar cells are considered to be promising candidates for the third-generation solar cells due to their excellent photovoltaic performance.The key to improve the power conversion efficiency of solar cells lies in the photovoltaic materials in the cells,and the photo-generated carrier process at the interface of photovoltaic materials is more closely related to its optoelectronic properties.Therefore,using theoretical calculation methods to explore the microscopic mechanism of different photovoltaic materials at the atomic level can provide a solid theoretical basis for the design of novel solar cells.Driven by these reasons,this paper exploit's high-level static electronic structure calculation combined with non-adiabatic molecular dynamic simulation method to explore the photocarrier dynamics of three types of photovoltaic materials with excellent performance,which is summarized as follows.(1)We rationally design and evaluate the photovoltaic performances of four TMD@fullerene heterostructures,i.e.,WSe₂@C₆₀,WSe₂@C₇₀,MoTe₂@C₆₀ and MoTe₂@C₇₀,respectively.Our simulation results indicate that the C₇₀-based heterostructures overall have better photoinduced electron transfer efficiencies than their C₆₀-based counterparts,among which the performance of the WSe₂@C₇₀ heterostructure is the best and the electron transfer from WSe₂ to C₇₀ almost accomplishes within 1 ps.In addition,the large build-in potential of about 0.75 e V of WSe₂@C₇₀ is beneficial for the charge separation processes.Our present work not only selects the van der Waals TMD@fullerene heterojunctions that might have excellent photovoltaic properties,but also paves the way for the rational design of novel heterojunctions with better optoelectronic performances.(2)Explored the ultrafast photoinduced dynamics at a non-fullerene D-A PTB7@PDI interface.Based on the results,it is found that such an interface exhibits distinct charge generation processes upon excitation with different wavelengths.The excitation at?591 nm mainly results in the local exciton|PTB7^*>.Later on,the electron transfer from PTB7 to PDI,i.e.,channel I charge generation process,occurs in 1ps.The situations are much more complex when the excitation is conducted using?487 nm light.The initial populated excitons include local excitons|PDI^*>,|PTB7^*>,and charge transfer exciton|PTB7⁺PDI^->,after which both channel I and channel II charge generation take place ultrafast.However,in both situations,the charge generation processes occur within a few picoseconds.Such ultrafast charge generation processes in a wide range of solar spectra are one of the reasons responsible for the excellent photovoltaic properties of such OSCs.(3)The interface band alignment properties of heterojunctions formed by monolayer MoS₂ and Cs Pb Br₃ nanosheets are investigated,and the effects of different interface contacts and SOC effects are considered.First,our results indicate that the interfacial properties are closely related to the contacting interfaces during the formation of the heterojunctions,and the band alignment alters from type-I to type-II,while the contacting facet of Cs Pb Br₃ changes from Pb Br₂-to Cs Br-terminated one.Moreover,the spin-orbit coupling effects are indispensable for correctly predicting such contacting interface-dependent band alignments of Cs Pb Br₃@MoS₂ heterojunctions.Finally,the non-adiabatic dynamics simulations reveal that the electron transfer from Cs Pb Br₃ to MoS₂takes place within 100 fs in type-II Cs Pb Br₃-Cs Pb@MoS₂ due to the small adjacent energy differences.Based on these results,we propose that such contacting interface-dependent band alignments might be responsible for the experimentally observed weakened instead of totally vanished photoluminescence.In conclusion,our present work not only provides a reasonable microscopic mechanism for the photodynamic process of the interface of photovoltaic materials of three kinds of new solar cells,but also provides a theoretical basis for the design of novel solar cells with better performance in the future.