Photovoltaic Performances Of Thick-film Polymer Solar Cells With Nonfullerene Acceptors

Polymer solar cells?PSCs?have attracted much attention in the past decades due to their various advantages such as low cost,light weight,flexible,and the potential of developing into large-area modules by solution processing method.With the rapid development in both novel electron donating materials and acceptor materials,power conversion efficiencies?PCEs?over 13%have been achieved in single junction PSCs.However,most photoactive materials afford PCE maxima in very small active layer thicknesses?80–120 nm?,especially in nonfullerene polymer solar cell.Thicker films can absorb incident light more efficiently,but the devices normally exhibited a sharp drop in the fill factor and thereby PCE.The active layer thickness restriction causes several issues for high throughput manufacturing of large area PSCs.In this dissertation,we mainly focus on performance of thick film polymer solar cells which contain nonfullerene acceptor component.In this dissertation,chapters 1 and 2 described the background and experiment methods for PSCs,respectively.In later research parts,low-bandgap conjugated polymer FBT-Th₄?1,4?with high hole mobility was appliedas a donor in non-fullerene PSCs.Firstly,we compared device performance with different thickness of active layer in non-fullerene polymer solar cells,with detailed analysis of photovoltaic performances of different nonfullerene acceptors in 300 nm thickness.Then,we introduced fullerene acceptor PC₇₁BM to modifypolymer-non-fullerene binary blend based on TSEH,a derivative of FBT-Th₄?1,4?.Interestingly,PC₇₁BMas the third component in the ternary-blend PSCs plays versatile functions.Ternary blend polymer solar cells that combine the fullerene and nonfullerene acceptors can obviously boost the photovoltaic performance.More detailed results are summarized as the following:In the third chapter,withFBT-Th₄?1,4?as donor,thick-film nonfullerene PSCs with ITIC or IDIC as the acceptor were compared.High performance nonfullerene PSCs based on active layers of 300 nm thicknesswere demonstrated.Thick-film?300 nm?nonfullerene PSC based on FBT-Th₄?1,4?:IDIC active layer with 0.25%DIO exhibited more superior PCE of 7.71%.The results demonstrate that the low-bandgap conjugated polymer with high hole mobility have a great potential for highperformance thick-film nonfullerene PSCs toward high-throughput solution-printingtechnology.In chapter four,we introduced fullerene acceptor PC₇₁BM as the third component for TSEH:IDIC binary blendPSCs,with active layers of²00 nm thickness.The PC₇₁BM in the ternary-blend PSCs plays important functions,including complementary light harvesting,facilitating exciton dissociation,enhancing charge transport,and optimizing the film morphology.Combining the merits of PC₇₁BM and IDIC acceptors,a significant enhancement of short-circuit current density relative to binary device could be achieved.The devices prepared from TSEH:IDIC:PC₇₁BM ternay blend layer with a1:0.6:1?by weight?ratio displayed the best performance of a 10.02%PCE,based on a J_scc of 20.05 mA cm^-2,an V_occ of 0.75 V,and a FF of 66.7%.The efficiency is 44%higher than an IDIC-based referencedevice and 317%higher than a PC₇₁BM-based reference device.The outstanding results demonstrate introducing fullerene acceptor into nonfullerene blends is an effective strategy to achieve high-efficiency in thick-film PSCs.