Effects Of Interfacial Modification Of PEDOT:PSS On Photovoltaic Performance In Organic Solar Cells

Organic solar cells（OSCs）have attracted widespread attention in the field of photovoltaic energy due to their lightweight,low cost,environmentally-friendly,and flexibility.Recently,OSCs has great potential with the continuous development,and its power conversion efficiency（PCE）has exceeded 19%.To further improve PCEs,most researchers are concentrating on study of the active layer,such as designing and synthesizing new donor/acceptor molecules,modulating the phase separation morphology of the active layer and so on.However,the performance of other layers is also critical for improving PCE,such as hole transport layer（HTL）.Poly（3,4-ethylenedioxythiophene/polystyrene sulfonate）（PEDOT:PSS）is widely employed as HTL in OSCs devices due to its low solution processing temperature,high optical transmittance and good mechanical flexibility.However,the core-shell structure of PEDOT:PSS leads to its low conductivity.And acidic PSS will corrode the transparent electrode ITO.PEDOT:PSS-based OSCs devices were limited in terms of photovoltaic performance and stability.In this thesis,modifying PEDOT:PSS by solvent post-treatment and organic base doping could solve the above problems.Meanwhile,the physical-chemical properties of modified PEDOT:PSS films and photovoltaic performance and stability of the devices were explored.The main contents are as follows:（1）Dimethyl sulfoxide（DMSO）,N,N-dimethylformamide（DMF）and ethylene glycol（EG）were employed as post-treatment solvents to modify PEDOT:PSS.The effects of solvent post-treatment were investigated on the physiochemical properties of PEDOT:PSS,photovoltaic performance and stability of devices.The results showed that the polar solvent facilitates the movement of PEDOT chain segments,which weakened the shielding effect of PSS on PEDOT,and the post-treatment process can remove effectively more PSS.Therefore,solvent post-treatment can significantly improve the conductivity of PEDOT:PSS films.In addition,PEDOT:PSS of solvent post-treatment was used as the HTL to fabricate OSCs devices based on PTB7-Th:PC₇₁BM.The PCE of the device increased from 8.41%to 9.34%.However,the stability of the devices was not significantly improved.（2）To further improve the device stability,the mild organic base imidazole（IM）was introduced as dopant to modify PEDOT:PSS.The effects of IM doping were investigated on the physiochemical properties of PEDOT:PSS,photovoltaic performance and stability of devices.Meanwhile,1-methylimidazole（MIM）was introduced as a contrast dopant to study the interaction between IM and PEDOT:PSS.The hydrogen bonding interactions between IM and PSS led to a conformational shift of PEDOT,which improved the conductivity of PEDOT:PSS film.OSCs devices based on PTB7-Th:PC₇₁BM were fabricated with PEDOT:PSS and PEDOT:PSS-IM as the HTL,and the PCE increased from 9.06%to 10.09%.In addition,the weak alkalinity of PEDOT:PSS-IM contribute to the excellent stability of the devices,which is mainly due to attenuated corrosion of PEDOT:PSS on ITO.