TY - JOUR

T1 - Diazirine-Based Photo-Crosslinkers for Defect Free Fabrication of Solution Processed Organic Light- Emitting Diodes

AU - Dey, Kaustav

AU - S. Roy, Chowdhury

AU - Dykstra, Erik

AU - Коронатов, Александр Николаевич

AU - Lu, H. Peter

AU - Shinar, Ruth

AU - Shinar, Joseph

AU - Anzenbacher, Pavel Jr

N1 - Publisher Copyright: © The Royal Society of Chemistry 2020.

PY - 2020/9/14

Y1 - 2020/9/14

N2 - The fabrication of solution deposited OLEDs is fraught with difficulties, largely due to the interlayer mixing and surface erosion during sequential deposition of the layers. We demonstrate that these problems can be circumvented by using photopolymerizable diazirine-based cross-linker capable of converting soluble organic materials into highly cross-linked insoluble networks. 3-Trifluoromethyl(aryl)diazirines photolyze readily upon the 10-15 min exposure of 365 nm UV irradiation to generate carbenes, which react with polymers or small moleculesviaC-H bond insertion producing highly cross-linked materials. This photo-generated cross-linking does not require any catalyst, initiator or short-wavelength UV light and is performed at room temperature, releasing molecular nitrogen as the only byproduct. To show the cross-linked polymer layers do not display inter-layer mixing, we deposited red-emitting regioregular poly(3-hexylthiophene-2,5-diyl) (P3HT) over cross-linked (10% cross-linker) blue emitting dioctyl polyfluorene (PFO) layer. The overlaid layers showed clear and well-defined boundary with no interlayer mixing. The surface morphology of the solution deposited layers was investigated by AFM to show that the cross-linked layers exhibited significant decrease in surface roughness. This is also shown on the example of the hole transporting material 4,4′-bis[N-(1-naphthyl)-N-phenylamino]-biphenyl (NPB) which displayed roughness average to decrease from 6.4 nm to 1.0 nm. The effect of decreased surface roughness on the performance of phosphorescent OLEDs was investigated by fabricating devices with configuration of ITO/PEDOT:PSS/NPB:(0%/5%/10%) cross-linker/MCP:6% Ir(mppy) 3/TPBI/CsF/Al. Following the diazirine-mediated cross-linking, the OLEDs displayed a decrease in turn-on voltage from 3.8 V to 3.0 V along with a six-fold enhancement of external quantum efficiency (EQE max) from 1.1% to 6.8% and maximum luminous efficiency increase from 3.8 cd A −1to 22.9 cd A −1. These results demonstrate that the simple diazirine mediated photo-cross-linking using mild conditions compatible with organic layers is a promising strategy for improving the performance of the solution-processed OLEDs.

AB - The fabrication of solution deposited OLEDs is fraught with difficulties, largely due to the interlayer mixing and surface erosion during sequential deposition of the layers. We demonstrate that these problems can be circumvented by using photopolymerizable diazirine-based cross-linker capable of converting soluble organic materials into highly cross-linked insoluble networks. 3-Trifluoromethyl(aryl)diazirines photolyze readily upon the 10-15 min exposure of 365 nm UV irradiation to generate carbenes, which react with polymers or small moleculesviaC-H bond insertion producing highly cross-linked materials. This photo-generated cross-linking does not require any catalyst, initiator or short-wavelength UV light and is performed at room temperature, releasing molecular nitrogen as the only byproduct. To show the cross-linked polymer layers do not display inter-layer mixing, we deposited red-emitting regioregular poly(3-hexylthiophene-2,5-diyl) (P3HT) over cross-linked (10% cross-linker) blue emitting dioctyl polyfluorene (PFO) layer. The overlaid layers showed clear and well-defined boundary with no interlayer mixing. The surface morphology of the solution deposited layers was investigated by AFM to show that the cross-linked layers exhibited significant decrease in surface roughness. This is also shown on the example of the hole transporting material 4,4′-bis[N-(1-naphthyl)-N-phenylamino]-biphenyl (NPB) which displayed roughness average to decrease from 6.4 nm to 1.0 nm. The effect of decreased surface roughness on the performance of phosphorescent OLEDs was investigated by fabricating devices with configuration of ITO/PEDOT:PSS/NPB:(0%/5%/10%) cross-linker/MCP:6% Ir(mppy) 3/TPBI/CsF/Al. Following the diazirine-mediated cross-linking, the OLEDs displayed a decrease in turn-on voltage from 3.8 V to 3.0 V along with a six-fold enhancement of external quantum efficiency (EQE max) from 1.1% to 6.8% and maximum luminous efficiency increase from 3.8 cd A −1to 22.9 cd A −1. These results demonstrate that the simple diazirine mediated photo-cross-linking using mild conditions compatible with organic layers is a promising strategy for improving the performance of the solution-processed OLEDs.

KW - CATHODE

KW - COPOLYMER

KW - DEVICES

KW - EMISSION

KW - HIGH-EFFICIENCY

KW - HOLE-TRANSPORT MATERIALS

KW - LAYER

KW - LINKING

KW - PERFORMANCE

KW - POLYMER

UR - http://www.scopus.com/inward/record.url?scp=85090598406&partnerID=8YFLogxK

UR - https://www.mendeley.com/catalogue/766d0af6-1a6d-312b-bcc6-750566043941/

U2 - 10.1039/D0TC02317E

DO - 10.1039/D0TC02317E

M3 - Article

VL - 8

SP - 11988

EP - 11996

JO - Journal of Materials Chemistry C

JF - Journal of Materials Chemistry C

SN - 2050-7526

IS - 34

ER -