Indoor Photovoltaics: Photoactive Material Selection, Greener Ink Formulations, and Slot-Die Coated Active Layers

Strong visible light absorption is essential to achieve high power conversion efficiency in indoor organic photovoltaics (iOPVs). Here, we report iOPVs that exhibit high efficiency with high voltage under excitation by low power indoor lighting. Inverted type organic photovoltaic devices with active layer blends utilizing the polymer donor PPDT2FBT paired with fullerene, perylene diimide, or ring-fused acceptors that are 6.5–9.1% efficient under 1 sun are demonstrated to reach efficiencies from 10 to 17% under an indoor light source. This performance transcends that of a standard silicon photovoltaic device. Moreover, we compared iOPVs with active layers both spin-cast and slot-die cast from nonhalogenated solvents and demonstrate comparable performance. This work opens a path towards high-efficiency iOPVs for low power electronics

Tin Oxide Electron Transport Layers for Air-/Solution-Processed Conventional Organic Solar Cells

Commercialization of organic solar cells (OSC) is imminent. Interlayers between the photoactive film and the electrodes are critical for high device efficiency and stability. Here, the applicability of SnO2 nanoparticles (SnO2 NPs) as the electron transport layer (ETL) in conventional OSCs is evaluated. A commercial SnO2 NPs solution in butanol is mixed with ethanol (EtOH) as a processing co-solvent to improve film formation for spin and slot-die coating deposition procedures. When processed with 200% v/v EtOH, the SnO2 NPs film presents uniform film quality and low photoactive layer degradation. The optimized SnO2 NPs ink is coated, in air, on top of two polymer:fullerene-based systems and a nonfullerene system, to form an efficient ETL film. In every case, addition of SnO2 NPs film significantly enhances photovoltaic performance, from 3.4 and 3.7% without the ETL to 6.0 and 5.7% when coated on top of PBDB-T:PC61BM and PPDT2FBT:PC61BM, respectively, and from 3.7 to 7.1% when applied on top of the PTQ10:IDIC system. Flexible, all slot-die-coated devices, in air, are also fabricated and tested, demonstrating the versatility of the SnO2 NPs ink for efficient ETL formation on top of organic photoactive layers, processed under ambient condition, ideal for practical large-scale production of OSCs

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

Exfoliated Graphene Composite Membrane for the All-Vanadium Redox Flow Battery

Vanadium redox flow batteries are emerging as a promising grid storage solution. Unlike competing flow battery concepts, these utilize vanadium in both the catholyte and anolyte chambers which enables easy regeneration and balancing of the cell upon crossover of species through the membrane during long-term use. To increase the time between regeneration cycles and to improve the overall efficiency of vanadium flow batteries, we investigate the use of an ultrathin, graphene coating on the surface of various Nafion membranes. Electrochemically exfoliated graphene (EEG) was dispersed at the air–water interface of a Langmuir–Blodgett trough, compressed, and transferred to Nafion 117 (180 μm thickness) and Nafion 115 (127 μm) membranes. Single-cell vanadium redox flow batteries assembled with the coated membranes led to significantly higher energy efficiency (increased by 13%), power density (by 67%), and discharge capacity (by 17.5%) over 100 cycles compared to uncoated Nafion. The graphene layer was stable over cycling, and electrochemical impedance spectroscopy and self-discharge experiments indicated that the improved battery performance is due to a combination of reduced vanadium crossover and enhanced electrochemical activity provided by the graphene at the electrode surface

Exfoliated Graphene Composite Membrane for the All-Vanadium Redox Flow Battery

Vanadium redox flow batteries are emerging as a promising grid storage solution. Unlike competing flow battery concepts, these utilize vanadium in both the catholyte and anolyte chambers which enables easy regeneration and balancing of the cell upon crossover of species through the membrane during long-term use. To increase the time between regeneration cycles and to improve the overall efficiency of vanadium flow batteries, we investigate the use of an ultrathin, graphene coating on the surface of various Nafion membranes. Electrochemically exfoliated graphene (EEG) was dispersed at the air–water interface of a Langmuir–Blodgett trough, compressed, and transferred to Nafion 117 (180 μm thickness) and Nafion 115 (127 μm) membranes. Single-cell vanadium redox flow batteries assembled with the coated membranes led to significantly higher energy efficiency (increased by 13%), power density (by 67%), and discharge capacity (by 17.5%) over 100 cycles compared to uncoated Nafion. The graphene layer was stable over cycling, and electrochemical impedance spectroscopy and self-discharge experiments indicated that the improved battery performance is due to a combination of reduced vanadium crossover and enhanced electrochemical activity provided by the graphene at the electrode surface