Fabrication And Performance For Fully Printable Organic Solar Cells

Organic Solar Cells（OSCs）have merits of being solution processable,good mechanical flexibility,low cost,and so on,which have attracted attention.With the rapid development of nonfullerene acceptors（NFAs）,the power conversion efficiency of small-area（about 0.1 cm²）OSCs has reached 19%for single-junction cells.This progress in efficiency stimulates OSCs from small-scale to commercial large-scale production.Full printing is highly desirable to realize large-scaling OSCs at low cost.However,OSCs with high performance are generally fabricated with spin-coated active layer and vacuum-deposited metal electrode.Fully printable OSCs with high performance are still a huge challenge in the field because of the lack of printable electrodes and transporting layers.This dissertation focuses on the development of printable electrode and transporting layers,the optimization of printing active layers,and the fabrication of fully printable OSCs.The main results are as follows:（1）Printable tansparent electrode:The silver nanowires（Ag NWs）electrode is a known transparent electrode with excellent optical and electrical performance.However,the large roughness of Ag NWs is prone to the electrical shortage,which limits its applications in the fully printable OSCs.To reduce the roughness of Ag NWs,we embedded Ag NWs into polyimide substrates（Ag NWs@PI）.This bottom transparent electrode shows a low surface roughness（1.5±0.5 nm）and low square resistance（26.0Ω/sq）.In the absorption region of NFAs（400-800 nm）,the average transmittance of Ag NWs@PI is comparable to ITO.With PM6:IT-4F as the active layer,the flexible devices demonstrated a high efficiency of 11.60%.In addition,Ag NWs@PI is also applicable to other nonfullerene active layers.（2）Printable active layer:Doctor-blade coating is one of the most effective methods for printing large-area OSCs.Active layers with high-boiling-point solvents have wide processing windows,which are easier to obtain uniform large-area films during doctor-blade coating.Y6 and Y6-1O show higher efficiencies when processed from low-boiling-point solvent of chlorofrom,while lower efficiencies when processed from high-boiling-point chlorobenzene.Instead,BTP-BO-4F,BTP-BO-4Cl,and BTP-e C9 can show high efficiencies when processed from both chloroform and chlorobenzene.The short side chains on the pyrrole ring（in Y6 and Y6-1O）cause excess aggregation when processed from chlorobenzene,while long side chains（in BTP-BO-4F,BTP-BO-4Cl,and BTP-e C9）inhibit such aggregation.Then,a 25.21 cm² organic solar module via doctor-blade coating based on PM6:BTP-e C9 was fabricated with an efficiency of 14.07%.The correlation between chemical structure of NFAs,device performance,and processing solvent will provide guidance for designing materials for printing OSCs.（3）Printable hole transporting layers:Conducting polymer poly（3,4-ethylenedioxythiophene）:poly（styrenesulfonate）（PEDOT:PSS）is widely used as a hole transporting layer in fully printable OSCs.However,PEDOT:PSS shows the following disadvantages:de-wetting issue,acidity,hydrophilicity,and insufficient work function（5.0 e V）.To solve these issues,an alcohol-dispersed formulation（PEDOT:F）was synthesized by adopting perfluorinated sulfonic-acid ionomers（PFSA）as counterions.Alcohol-dispersed PEDOT:F has a small contact angle when coated on active layers.The PEDOT:F films are hydrophobic due to the hydrophobicity of C-F bonds.The dissociation of acids in alcohol-dispersed PEDOT:F can be suppressed.In addition,the work function of PEDOT:F（5.4-5.7 e V）is higher than PEDOT:PSS.OSCs based on different fullerene and nonfullerene active layers were fabricated with PEDOT:F.The efficiencies of PEDOT:F-based cells are comparable with the Mo O₃-based reference cells.PEDOT:F shows good hole transporting performance in both conventional and inverted structures.The alcohol-dispersed PEDOT:F exhibits great potential in printing organic electronics.（4）Fully printed OSCs:Based on the above studies of Ag NWs electrodes,doctor-bladed active layers,and PEDOT:F hole transporting layers,the fully printable OSCs with the structure of glass/Ag NWs/PEI-Zn/PM6:Y6:PC₇₁BM/PEDOT:F/Ag NWs are fabricated.The devices show efficiencies of 14.62%for the small-area（0.041 cm²）device,and 13.07%for the large-area（12.2 cm²）module.Furthermore,the the fully printable OSCs based on PEDOT:F show great stability under high humidity and operating conditions.