Fabrication,mechanism And Application Research Of Highly-Efficient Ternary Organic Solar Cells

Organic solar cells（OSCs）have showcased great potential for solution processing of flexible,light-weight and semitransparent devices.Due to the rapid development of versatile fused-ring electron acceptors（FREAs）,single-junction OSCs with binary blends of polymer donors and FREAs as active layers have frequently refreshed the record power conversion efficiency（PCE）.Harvesting as wide as possible range of the solar spectrum is thus highly demanded for the light-absorbing active layers,which often limits the PCEs of binary OSCs.An effective strategy to broaden the absorption width of the binary bulk-heterojunction（BHJ）OSCs is to use ternary blend,where a third component（donor or acceptor）with complementary absorption and suitable energy levels is incorporated into the binary hosts.Searching for suitable third components is crucial but challenging in exploring high-efficient ternary OSCs.The main reason lies in the modulation of more complicated morphology and charge transport among photovoltaic materials in ternary blends with the induced third component.Secondly,most highly-efficient OSCs adopting BHJ blends of electron donors and acceptors achieve their maximum PCEs with active layers thicknesses（～100 nm）and small device areas（ca.0.04 cm²）.Such thin films can’t harvest all photons in their spectral range.As increasing the thickness,however,the PCEs drop fast.It is thus very challenging to achieve high-performance large-area thickness-tolerant devices for practical application.Thirdly,the ternary strategy needs to be applied into semitransparent devices.Finally,suitable third components often face the challenges in structure design and operation generality for wide binary blends systems.To address the above mentioned issues,we rationally modulate the intermolecular interaction between the additional component and the host materials to enhance the microscopic morphology and charge dynamics process of the active layer,and then achieve a series of ternary OSCs with high efficiency and stability.The main research contents and innovations of this thesis are summaried as follows:Firstly,we have developed highly-efficient ternary OSCs by introducing a high electron mobility acceptor PC₆₁BM as third component into PM6:ITC6-4F host blends.The PCE of the ternary OSCs reached 15.11%with a J_SC of 20.78 m A cm^-2,a V_OC of 0.93 V and a FF of 78.18%for the PC₆₁BM content of 10 wt%in the acceptors.The PCE of 15.11%and the FF of 78.18%are among the highest values for ternary OSCs.An approximately 13%PCE improvement was achieved compared with ITC6-4F based binary OSCs.Detailed studies suggest that the addition of PC₆₁BM not only enhances the electron mobility of the derived BHJ blend but also facilitates exciton dissociation,resulting in a more balanced charge transport alongside with reduced trap-assisted charge recombination.This work suggests that utilizing the complementary advantages of fullerene and FREAs is a promising way to finely tune the detailed photovoltaic parameters and further improve the PCEs of OSCs.Based on the study in the previous section,in Chapter 3,we report high-performance large-area and thick-film ternary OSCs by incorporating high electron mobility IDIC into PM6:IM-4F host blend.The addition of IDIC significantly improves the crystallinity and intensifies face-on orientation in proper multi-length morphology for enhanced charge transport in active layers.As a result,the optimized～100 nm-thick ternary OSCs with 10 wt%IDIC in the acceptors exhibit a high PCE of 15.86%for small-area（0.04 cm²）and 14.80%for large-area（0.50 cm²）devices.Importantly,the optimal ternary OSCs present excellent tolerance to the active layer thickness（≈65–353 nm）.The 282 nm-thick devices contribute a PCE of 14.43%and a FF of71.23%,among the highest values for OSCs with similar active layer thicknesses reported to date,even outperforming the remarkable 300 nm-thick PM6:Y6 system.Our work demonstrates that ternary OSCs by introducing high mobility acceptor as third component to host binary blends featuring high current and low energy loss have great potential for large-scale fabrication of highly-efficient thick-film OSCs for practical application.In Chapter 4,we report herein an efficient ternary strategy in achieving highly efficient PBDB-T based devices by incorporating two alloy-forming FREAs with distinct structural orders.INPIC-Si as the third component showcases a relatively narrower bandgap and higher energy levels than the host acceptor IDTO-T-4F.Featuring good compatibility and alloy-forming blends,two FREAs generate F?rster resonance energy transfer from IDTO-T-4F to INPIC-Si,facilitating efficient exciton dissociation and charge carrier transport.Importantly,the introduced low crystalline INPIC-Si decreases the strong aggregation of PBDB‐T:IDTO-T-4F blends for optimal phase-separation and structural order.Consequently,the optimal PBDB‐T:IDTO-T-4F:INPIC-Si ternary OSCs deliver a champion PCE of 14.55%with simultaneously improved device parameters over binary ones.To the best of our knowledge,this performance is among the highest for PBDB-T-based ternary OSCs in the literature.Our work demonstrates the incorporation of a narrow bandgap FREA with low structural order to heavily aggregated binary blends can optimize the blend morphology for reduced energy loss and significantly improved the photovoltaic performance in ternary OSCs.Based on the study in Chapter 4,we further report high-performance ternary semitransparent OSCs by incorporating low structure order and energy level matching DCB-4F as third component into PM6:DTPSe-4Cl host blend.The DTPSe-4Cl exhibits high degree of planarity to form a strong interaction with DCB-4F and thus suppress the aggregation of active layer.The addition of DCB-4F enhances the molecular arrangement in proper multi-length morphology for enhanced charge transport in active layers.As a result,outstanding PCEs of 15.93%and 12.58%are achieved for the corresponding opaque and semitransparent ternary OSCs,respectively.These results indicate that the ternary strategy by introducing low structure order arrangement and low energy loss is promising for preparing highly-efficient semitransparent OSCs.In Chapter 6,we aim to address the challenges in developing suitable third components often in structure design and operation generality for wide binary blends systems and a simple dithieno[3,2-b:2′,3′-d]pyrrole-rhodanine molecule（DR8）was thus designed as versatile and cost-effective third component for high-performance nonfullerene OSCs.By employing classic ITIC-like ITC6-4Cl and Y6 as model nonfullerene acceptors（NFAs）in PM6-based binary blends,DR8 added PM6:ITC6-4Cl blends exhibit significantly promoted energy transfer and exciton dissociation.The PM6:ITC6-4Cl:DR8（1:1:0.1,weight ratio）OSCs contribute an exciting PCE of 14.94%in comparison to host binary devices（13.52%）,while PM6:Y6:DR8（1:1.2:0.1）blends enable 16.73%PCE with all simultaneously improved photovoltaic parameters.To the best of the knowledge,this performance is among the best for ternary OSCs with simple small molecular third components in the literature.More importantly,DR8-added ternary OSCs exhibit much improved device stability against thermal aging and light soaking over binary ones.This work provides new insight on the design of efficient third components for OSCs.