Design And Performance Study Of New Perylene-Diimide Cathode Interlayers For Organic Solar Cells

Organic solar cells are a new type of clean renewable energy technology that has received widespread attention and research,because of its unique advantages such as light weight,flexibility,translucency,low cost,and adaptability to roll-to-roll printing production technology.In recent years,the energy conversion efficiency of organic solar cells has been rapidly improved due to the innovation and progress in material design and device engineering.As an important component of organic solar cells,cathode interlayer can effectively improve the efficiency and stability of the cells.Currently,aromatic imide cathode interlayer materials stand out among various interlayer materials because of their high electron affinity,high electron mobility and low cost.Nevertheless,the development of cathode interlayer materials has lagged behind the rapidly advancing active layer materials,and further research on the molecular design and working mechanism of cathode interlayer materials is still needed.Therefore,this thesis investigates the improvement of cathode interface modification for organic solar cells based on aromatic imine cathode interface modification layer materials.The main research results are as follows:1.Cathode engineering with perylene-diimide interlayer enabling over 17%efficiency single-junction organic solar cell.In organic solar cells(OSCs),cathode interfacial materials are generally designed with highly polar groups to increase the capability of lowering the work function of cathode.However,the strong polar group could result in a high surface energy and poor physical contact at the active layer surface,posing a challenge for interlayer engineering to address the trade-off between device stability and efficiency.Herein,we report a hydrogen-bonding interfacial material,aliphatic amine-functionalized perylene-diimide(PDINN),which simultaneously down-shifts the work function of the air stable cathodes(silver and copper),and maintains good interfacial contact with the active layer.The OSCs based on PDINN engineered silvercathode demonstrate a high power conversion efficiency of 17.23%(certified value 16.77% by NREL)and high stability.Our results indicate that PDINN is an effective cathode interfacial material and interlayer engineering via suitable intermolecular interactions is a feasible approach to improve device performance of OSCs.2.Fluorinated Perylene-diimides: Cathode Interlayers Facilitating Carrier Collection for High-Performance Organic Solar Cells.Organic solar cells(OSCs)have experienced rapid progress with the innovation of near-infrared(NIR)-absorbing small-molecular acceptors(SMAs),while the unique electronic properties of the SMAs raise new challenges in relation to cathode engineering for effective electron collection.To address this issue,two fluorinated perylene-diimides(PDIs),PDINN-F and PDINN2 F,are synthesized by a simple fluorination method,for application as cathode interlayer materials(CIM).The two bay-fluorinated PDI-based CIMs possess a lower lowest unoccupied molecular orbital(LUMO)energy level of ≈-4.0 e V,which improves the energy level alignment at the NIR-SMAs(such as BTP-e C9)/CIM for a favorable electron extraction efficiency.The monofluorinated PDINN-F shows higher electron mobility and better improved interfacial compatibility.The PDINN-F-based OSCs with PM6:BTP-e C9 as active layer exhibit an enhanced fill factor and larger short-circuit current density,leading to a high power conversion efficiency(PCE)exceeding 18%.The devices with PDINNF CIM retain more than 80% of their initial PCE after operating at the maximum power point under continuous illumination for 750 h.This work prescribes a facile,cost-effective,and scalable method for the preparation of stable,highperformance fluorinated CIMs,and instilling promise for the NIR-SMAs-based OSCs moving forward.3.Based on PDINN with the same aliphatic amine as the polar group.two aromatic imines with different aromatic π-conjugated cores,PDINN4 Cl with a tetrachloro-substituted perylene core and NDINN with a naphthalene core,were used as cathodic interface modification layer materials.The core structures were used to modulate the absorption properties of the cathodic interface layer.The tetrachloro-substituted perylene caused absorption blueshift because of the distorted core structure.Meanwhile naphthalene showed a more blue-shifted absorption due to its smaller conjugated structure.The molecular energy levels of the cathodic interfacial layer were further adjusted to achieve a better energy level match between the molecules and the acceptor.The tetrachlorosubstitution on the perylene core can effectively lower its molecular energy level,and naphthalene also exhibits a lower molecular energy level.However,the final efficiency of both NDINN and PDINN4Cl-based devices performed poorly,which was related to their low electron mobility.The results demonstrate that designing perylene diiimides as cathode interface modification layers requires avoiding distortion and spatial site resistance of the central core.