Systematic Investigation of Core and Endcap Selection on the Development of Functional π‑Conjugated Materials

We investigate the optoelectronic properties of four new π-conjugated materials, which feature either a 3,4-ethylenedioxythiophene (EDOT) or an EDOT-flanked benzothiadiazole aryl core with two N-annulated perylene diimide (NPDI) or theobromine endcaps. Endcap selection was an important factor for the preferred molecular geometry, where the use of NPDI endcaps induced a dragonfly-type conformation and the use of theobromine endcaps promoted a corkscrew-like conformation. Electrochemically, the choice of aryl π-conjugated core was found to have a strong influence on the molecule’s highest occupied molecular orbital (HOMO) energy level, while the choice of endcap had a more profound effect on the lowest unoccupied molecular orbital (LUMO) energy level. Although the optical absorption profiles were generally dominated by endcap contributions, using the larger EDOT-flanked benzothiadiazole aryl core was found to decrease the optical energy band gap. Proof-of-concept organic photovoltaic (OPV) devices, using a PM6:Y6 bulk heterojunction (BHJ) photoactive layer, were fabricated using the four new π-conjugated materials as the cathode interlayer (CIL). The molecules featuring the EDOT aryl core (A and B) enabled OPV device power conversion efficiencies (PCEs) by around 12%, comparable to control devices using PDINN as the CIL, while those featuring the EDOT-flanked benzothiadiazole aryl core (C and D) obtained PCEs of 10.5%. The observed differences in OPV device performance were attributed to superior solubility and subsequent CIL film formation in the case of A and B, compared to C and D, which, in turn, led to improved contact between the Ag top electrode and the BHJ photoactive layer

Room-Temperature Photodeposited Amorphous VO_<i>x</i> Hole-Transport Layers for Organic Devices

Hole-transport layers (HTLs) and hole-injection layers (HIL) are an integral part of optoelectronic devices such as organic photovoltaic cells (OPVs) and organic light-emitting diodes (OLEDs). A class of materials commonly used as HTLs are metal oxides because they have high transparency and stability. These metal oxides are, however, often made using techniques that are not conducive to large-scale fabrication, a challenge that must be resolved for the widespread adoption of these devices. In this work, we demonstrate the use of a room-temperature, ambient photochemical deposition route to form vanadium oxide films. We show, using a combination of X-ray absorption and X-ray photoemission spectroscopies, that the VOx film consists of V2O5 but with a significant amount of V4+ present. These films are initially created amorphous and become nanocrystalline after annealing in air at a temperature of 250 °C. After incorporating these VOx thin films as HTLs in both OPV and OLED devices, we surprisingly find this increase in crystallinity does not translate to improvement in device performance. All devices perform similarly toor better thancontrol devices using PEDOT:PSS as an HTL. We furthermore demonstrate that these films are not affected by the operation of these devices and that the technique can be employed in combination with slot-die coating printing techniques. This work provides an easily upscaled, low-temperature method for depositing metal-oxide HTL layers

Water-Processable Self-Doped Hole-Injection Layer for Large-Area, Air-Processed, Slot-Die-Coated Flexible Organic Light-Emitting Diodes

Hole-injection layers (HILs) play a pivotal role in organic light-emitting diodes (OLEDs) by enabling the efficient injection of positive charge carriers (holes) into the active layer, thus facilitating light emission. This research paper focuses on enhancing the processability and performance of solution-processed HILs in OLEDs by utilizing a water-processable self-doped polymer, P2. The P2 film, deposited via slot-die coating, exhibits exceptional uniformity, high transmittance (85%) across the visible spectrum, and a smooth surface (with a root-mean-square roughness of 1.4 nm) comparable to state-of-the-art poly­(3,4-ethylenedioxythiophene):poly­(styrenesulfonate) (PEDOT:PSS) films. The P2 HIL in a four-layer OLED structure, consisting of a PET/ITO/HIL/hole transport layer (HTL)/emissive layer (EML)/electron transport layer (ETL)/Ag, with poly­(9-vinylcarbazole) (PVK) as the HTL, Super Yellow (SY) as the EML, and poly­((9,9-bis­(3′-(N,N-dimethylamino)­propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)) (PFN) as the ETL, demonstrates enhanced hole injection and transport properties. Flexible OLEDs incorporating P2 HILs, fabricated and tested under ambient conditions on a large-area (4 × 40 mm) indium–tin oxide (ITO)-coated polyethylene terephthalate (PET) substrate, demonstrate a maximum current efficiency of 1.24 cd/A, surpassing devices with PEDOT:PSS HILs by 82%. Moreover, a significant 50% reduction in turn-on voltage is observed compared with analogous devices using a PEDOT:PSS layer. This work contributes to the advancement of the OLED technology for various commercial optoelectronic applications

Water-Processable Self-Doped Hole-Injection Layer for Large-Area, Air-Processed, Slot-Die-Coated Flexible Organic Light-Emitting Diodes

Hole-injection layers (HILs) play a pivotal role in organic light-emitting diodes (OLEDs) by enabling the efficient injection of positive charge carriers (holes) into the active layer, thus facilitating light emission. This research paper focuses on enhancing the processability and performance of solution-processed HILs in OLEDs by utilizing a water-processable self-doped polymer, P2. The P2 film, deposited via slot-die coating, exhibits exceptional uniformity, high transmittance (85%) across the visible spectrum, and a smooth surface (with a root-mean-square roughness of 1.4 nm) comparable to state-of-the-art poly­(3,4-ethylenedioxythiophene):poly­(styrenesulfonate) (PEDOT:PSS) films. The P2 HIL in a four-layer OLED structure, consisting of a PET/ITO/HIL/hole transport layer (HTL)/emissive layer (EML)/electron transport layer (ETL)/Ag, with poly­(9-vinylcarbazole) (PVK) as the HTL, Super Yellow (SY) as the EML, and poly­((9,9-bis­(3′-(N,N-dimethylamino)­propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)) (PFN) as the ETL, demonstrates enhanced hole injection and transport properties. Flexible OLEDs incorporating P2 HILs, fabricated and tested under ambient conditions on a large-area (4 × 40 mm) indium–tin oxide (ITO)-coated polyethylene terephthalate (PET) substrate, demonstrate a maximum current efficiency of 1.24 cd/A, surpassing devices with PEDOT:PSS HILs by 82%. Moreover, a significant 50% reduction in turn-on voltage is observed compared with analogous devices using a PEDOT:PSS layer. This work contributes to the advancement of the OLED technology for various commercial optoelectronic applications

Water-Processable Self-Doped Hole-Injection Layer for Large-Area, Air-Processed, Slot-Die-Coated Flexible Organic Light-Emitting Diodes

Hole-injection layers (HILs) play a pivotal role in organic light-emitting diodes (OLEDs) by enabling the efficient injection of positive charge carriers (holes) into the active layer, thus facilitating light emission. This research paper focuses on enhancing the processability and performance of solution-processed HILs in OLEDs by utilizing a water-processable self-doped polymer, P2. The P2 film, deposited via slot-die coating, exhibits exceptional uniformity, high transmittance (85%) across the visible spectrum, and a smooth surface (with a root-mean-square roughness of 1.4 nm) comparable to state-of-the-art poly­(3,4-ethylenedioxythiophene):poly­(styrenesulfonate) (PEDOT:PSS) films. The P2 HIL in a four-layer OLED structure, consisting of a PET/ITO/HIL/hole transport layer (HTL)/emissive layer (EML)/electron transport layer (ETL)/Ag, with poly­(9-vinylcarbazole) (PVK) as the HTL, Super Yellow (SY) as the EML, and poly­((9,9-bis­(3′-(N,N-dimethylamino)­propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)) (PFN) as the ETL, demonstrates enhanced hole injection and transport properties. Flexible OLEDs incorporating P2 HILs, fabricated and tested under ambient conditions on a large-area (4 × 40 mm) indium–tin oxide (ITO)-coated polyethylene terephthalate (PET) substrate, demonstrate a maximum current efficiency of 1.24 cd/A, surpassing devices with PEDOT:PSS HILs by 82%. Moreover, a significant 50% reduction in turn-on voltage is observed compared with analogous devices using a PEDOT:PSS layer. This work contributes to the advancement of the OLED technology for various commercial optoelectronic applications

Water-Processable Self-Doped Hole-Injection Layer for Large-Area, Air-Processed, Slot-Die-Coated Flexible Organic Light-Emitting Diodes

Hole-injection layers (HILs) play a pivotal role in organic light-emitting diodes (OLEDs) by enabling the efficient injection of positive charge carriers (holes) into the active layer, thus facilitating light emission. This research paper focuses on enhancing the processability and performance of solution-processed HILs in OLEDs by utilizing a water-processable self-doped polymer, P2. The P2 film, deposited via slot-die coating, exhibits exceptional uniformity, high transmittance (85%) across the visible spectrum, and a smooth surface (with a root-mean-square roughness of 1.4 nm) comparable to state-of-the-art poly­(3,4-ethylenedioxythiophene):poly­(styrenesulfonate) (PEDOT:PSS) films. The P2 HIL in a four-layer OLED structure, consisting of a PET/ITO/HIL/hole transport layer (HTL)/emissive layer (EML)/electron transport layer (ETL)/Ag, with poly­(9-vinylcarbazole) (PVK) as the HTL, Super Yellow (SY) as the EML, and poly­((9,9-bis­(3′-(N,N-dimethylamino)­propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)) (PFN) as the ETL, demonstrates enhanced hole injection and transport properties. Flexible OLEDs incorporating P2 HILs, fabricated and tested under ambient conditions on a large-area (4 × 40 mm) indium–tin oxide (ITO)-coated polyethylene terephthalate (PET) substrate, demonstrate a maximum current efficiency of 1.24 cd/A, surpassing devices with PEDOT:PSS HILs by 82%. Moreover, a significant 50% reduction in turn-on voltage is observed compared with analogous devices using a PEDOT:PSS layer. This work contributes to the advancement of the OLED technology for various commercial optoelectronic applications