Fabrication And Key Scientific Issues Investigation Of Semitransparent Organic Photovoltaics

Organic photovoltaics（OPVs）as a clean energy technology have attracted much attentions in the world due to their unique advantages of lightweight,flexibility,large area preparation,and semitransparency in particular.In 2018,Academician Li Yongfang pointed out that"it is expected that flexible and semitransparent OPVs will be practical application in the next 5-10 years",which is published in Science Focus,Vol.13,No.4 with the article title of"organic photovoltaic materials and devices".At present,the research key points of semitransparent OPVs is focused on further improving device performance to meet the practical application needs in the future.In this dissertation,material selection of active layer,photon harvesting optimization of active layer and the preparation of high performance transparent electrode are the pointcuts,for improving power conversion efficiency（PCE）and average visible transmittance（AVT）of semitransparent OPVs.The relationships among material property,new selection principles,preparation process,working mechanism and performance of semitransparent OPVs were investigated.The main research contents and innovation points can be summarized as follows:（1）A new material selection method was proposed based on the complementary photovoltaic parameters of binary OPVs.The 11.60%PCE of ternary OPVs is achieved by employing polymer material J71 as donor,nonfullerene materials IT-M and ITIC with excellent compatibility as acceptor.The J71:IT-M and J71:ITIC based binary OPVs exhibit complementary photovoltaic parameters,and their respective advantages can be interated into the ternary OPVs by regulating IT-M:ITIC ratios.（2）For ternary OPVs based on one donor and two acceptors,a material selection strategy was proposed by employing acceptors with similar lowest unoccupied molecular orbital（LUMO）levels.The ternary OPVs with PM6:IPTBO-4Cl:MF1 as active layer were successfully prepared.Regardless of the mixture of the accepter materials IPTBO-4Cl and MF1 in any proportion,the prepared ternary OPVs can maintain relatively high fill factor（>72%）,which should be attributed to the good compatibility between the used materials and the similar LUMO levels between two accepters.By regulating acceptors ratio,the 15.74%PCE of ternary OPVs can be achieved.（3）The ternary strategy was introduced into semitransparent OPVs.The PCE of semitransparent OPVs can be effectively improved by introducing narrower band gap materal as the third component.Semitransparent OPVs were fabricated by using narrow-band gap polymer PTB7-Th as donor and nonfullerene material BDTTh IT-4F as acceptor,the narrower band gap material IEICO-4F as the third component,the PCE and AVT of ternary semitransparent OPVs arrive to 9.40%and 24.6%,respectively.Compared with binary semitransparent OPVs,the PCE of ternary semitransparent OPVs is increased by12.6%,and the AVT loss is less than 2.8%.The PCE improment of ternary semitransparent OPVs are attributed to that the introduction of narrower band gap material expand photon harvesting of active layer in near-infrared light range.（4）Based on the characteristic that hole transport network can be easily formed in polymer donor,a new strategy was proposed for fabricating semitransparent OPVs by regulating ratios of polymer donor and nonfullerene small molecule acceptor in active layers.Appropriate reduction of the polymer donor content in active layers can improve the visible light transmittance of semitransparent OPVs and balance the transport of holes and electrons for improving performance of semitransparent OPVs.In PTB7-Th:IEICO-4F system,when the donor:acceptor weight ratios are reduced from 1.2:1.5 to 0.8:1.5,27.1%AVT and 9.06%PCE can be obtained in semitransparent OPVs.The AVT of semitransparent OPVs is increased by more than 14.3%,while PCE is decreased by less than 4.5%.（5）The material selection method was proposed by employing wide band gap donor and narrow band gap acceptor to fabricate semitransparent OPVs,achieving 12.37%PCE and 18.6%AVT.The open circuit voltage(V_OCs)of semitransparent OPVs with narrow gap donor/narrow gap acceptor are relatively low,which limit the PCE of semitransparent OPVs.The semitransparent OPVs were fabricated with wide band gap polymer PM6 as donor and narrow band gap nonfullerene material Y6 as acceptor.By adjusting thickness of active layer,the photon harvesting efficiency and the visible light transmittance of active layer can be optimized;by adjusting thickness of transparent top electrode,the visible light transmittance and electrical conductivity of transparent top electrode can be balanced,which are beneficial to fabricate high performance semitransparent OPVs.（6）Based on wide band gap donor/narrow band gap acceptor,the PCE and AVT of semitransparent OPVs can be simultaneously optimized by regulating donor/acceptor ratios and the third component doping ratios.The semitransparent OPVs with wide band gap donor/narrow band gap acceptor generally exhibited relativel high PCE and relatively low AVT.By regulating donor/accepter ratios and introducing the third component with narrower band gap to balance the photon harvesting ability of the active layer in different spectral ranges,ternary semitransparent OPVs based on D18-Cl:Y6-1O:Y6 as active layer were successfully prepared,achieving 13.02%PCE and 20.2%AVT.This dissertation has a total of 69 pictures,17 tables,and 188 references.