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We report the confinement of recombination zone (RZ) in green phosphorescent organic light-emitting diodes (Ph-OLEDs) for enhanced efficiency by varying the emission layer (EML) thickness and through quantum well (QW) insertion. At low thickness of EML, the efficiency is reduced owing to the diffusion of the RZ toward the EML/hole transport layer interface, which was revealed through the presence of exciton blocking layer [TCTA: tris(4-carbazoyl-9-ylphenyl)amine] excitation accompanied by a blue-shift in electroluminescence (EL). Further increase in the thickness of the EML caused the RZ to move toward the cathode, which was determined based on the disappearance of TCTA emission and the corresponding red-shift observed in EL spectra. The solid-state and time-resolved area normalized photoluminescence emission spectra investigations further corroborate the RZ movement tactics along with TCTA excimer generation and exciplex generation between TCTA and tris[2-phenylpyridinato-C2,N]iridium(III) Ir(ppy)3. The superior quantum and current efficiency of 14.4% and 50 cd/A, respectively, were determined for the device with an EML thickness of 15 nm due to the confinement of the RZ in the EML. The addition of (EML/interlayer/EML) QW facilitates improved charge balance in the Ph-OLED and further assists in the confinement of the RZ in the EML. Because of QW, a slight increment in quantum (14.6%) and current efficiency (52 cd/A) was observed. Without using any sensing layers, movement of the RZ was successfully monitored and confined in the EML to realize enhanced efficiency in green Ph-OLEDs.

This study presents a preliminary investigation of the application of MAPbI3perovskite solar cells (PSCs) as dosimeters for space and medical purposes. Specifically, it explores the effects of 6 MeV electron beam exposure on the performance and degradation mechanisms of PSC devices. The study also employs crystallographic, optical, and simulation-based analyzes to gain insights into the degradation process. The findings of this research lay the groundwork for the development of an advanced radiation detection structure, combining a scintillator with a photocounting PSC device, as a potential replacement for existing silicon photomultipliers in the future. The PSC devices exhibit an initial power conversion efficiency of approximately 14%. However, under electron fluences ranging from 3 to 21 kGy, a gradual degradation is observed, characterized by a decline in open-circuit voltage and short-circuit current. Beyond the 9 kGy threshold, the device performance deteriorates significantly, with a 52% decrease compared with the initial performance, which is primarily attributed to a decrease in the fill factor. Through X-ray diffraction, time-resolved photoluminescence, and density functional theory simulations, the research uncovers that continuous electron beam exposure induces the formation of crystallographic defects and shallow traps, leading to the gradual deterioration of device performance postirradiation.

Low-temperature annealing of Zinc oxide (ZnO) films as electron transport layers for inverted polymer solar cells was investigated. A wrinkled morphology of the ZnO film has previously been mostly observed after dynamic annealing (DA). In this study, we investigated the effect of static annealing (SA) of ZnO layers deposited by the sol–gel method at 25 °C, 150 °C, and 200 °C for 10 min in air. We observed the formation of the wrinkle structures on the surface of the ZnO sample annealed at 150 °C, while flat structures were formed at 200 °C. Here, a variable ramping/heating rate provided by a static annealing process resulted in a variable solvent evaporation rate and transformation of the precursor. The tensile stresses induced by slower heating (∼40 °C/min in a 0.75 M ZnO solution) and residual solvent resulted in an amorphous layer with a wrinkled structure at a low temperature of 150 °C. A flat structure was obtained with slightly different dynamics at a faster heating rate (∼56 °C/min) at 200 °C. Consequently, the SA process enabled us to fabricate the desired wrinkled morphology at lower annealing temperatures (e.g., 150 °C) than ever reported for DA processes; the ramp rate in the 200 °C SA process was too high to form the wrinkled structure. The short circuit current of the device using a wrinkle structure was better than that of the device with flat structure due to optical effects of internal reflection, scattering and light-trapping by wrinkles, while the transmittance and fill factor of the device using a flat ZnO layer annealed at 200 °C was better than those of the device with a ZnO layer annealed at 150 °C. This was due to better film quality from the higher processing temperature, a low surface roughness, and less defects. However, the power conversion efficiency of devices with both films was similar, meaning that the low temperature annealing process producing the wrinkle structure can be used for fabricating devices with polymer substrates and gas barriers for flexible electronics. In the case of the wrinkled structure, we observed that the wrinkle height was highly dependent on the ramping rate, ZnO solution concentration, and annealing temperature, compared with previous works.

We studied the effect of direct charge trapping at different doping concentrations on the device performance in tris(8-hydroxyquinoline) aluminum (Alq3):10-(2-benzothiazolyl)-2,3,6,7-tetrahydro-1,1,7,7-tetramethyl-1H,5H,11H-(1)-benzopyropyrano(6,7–8-i,j)quinolizin-11-one (C545T) as a host–dopant system of a fluorescent organic light-emitting diode. With increasing C545T doping concentration, trap sites could lead to the promotion of hole injection and the suppression of electron injection due to the electron-transport character of Alq3host for each carriers, as confirmed by hole- and electron-only devices. Direct charge injection of hole carriers from the hole transport layer into C545T dopants and the charge trapping of electron carriers are the dominant processes to improve the charge balance and the corresponding efficiency. The shift of the electroluminescence (EL) spectra from 519 nm to 530 nm was confirmed the exciton formation route from Förster energy transfer of host–dopant system to direct charge trapping of dopant-only emitting systems. Variation in the doping concentration dictates the role of the dopant in the fluorescent host–dopant system. Even though concentration quenching in fluorescent dopants is unavoidable, relatively heavy doping is necessary to improve the charge balance and efficiency and to investigate the relationship between direct charge trapping and device performance. Heavy doping at a doping ratio of 6% also generates heavy exciton quenching and excimer exciton, because of the excitons being close enough and dipole–dipole interactions. The optimum device performance was achieved with a 4%-doped device, retaining the high efficiency of 12.5 cd/A from 100 cd/m2up to 15 000 cd/m2.

The effect of varying degrees of surface and vertical coverage of gold nanoparticles (Au-NPs) by poly(styrenesulfonate)-doped poly(3,4-ethylenedioxythiophene) (PEDOT:PSS), which was used as a capping layer between indium tin oxide (ITO) and a hole transport layer (HTL) on small-molecule fluorescent organic light-emitting diodes (OLEDs), was systemically investigated. With respect to the Au-NP loading amount and size, the resultant current densities influenced the charge balance and, therefore, the OLED device performance. When the capping layer consisted of ITO/Au-NPs/PEDOT:PSS+Au-NPs, superior device performance was obtained with 10-nm Au-NPs through increased surface coverage in comparison to other Au-NP PEDOT:PSS coverage conditions. Furthermore, the Au-NP size determined the vertical coverage of the capping layer. The current densities of OLEDs containing small Au-NPs (less than 30 nm, small vertical coverage) covered by PEDOT:PSS decreased because of the suppression of the hole carriers by the Au-NP trapping sites. However, the current densities of the devices with large Au-NPs (over 30 nm, large vertical coverage) increased. The increased electromagnetic fields observed around relatively large Au-NPs under electrical bias were attributed to increased current densities in the OLEDs, as confirmed by the finite-difference time-domain simulation. These results show that the coverage conditions of the Au-NPs by the PEDOT:PSS clearly influenced the OLED current density and efficiency.

Toxic doping gases are usually used to produce hydrogenated amorphous silicon (a-Si:H) layers in thin-film solar cells (TFSCs). Hence, an alternative structure that avoids the use of toxic gases is desirable. In this work, we replaced both the p-type-a-Si:H and n-type-a-Si:H layers simultaneously in a normal TFSC to form a structure that is dopant-free. Molybdenum oxide (MoO3) and lithium fluoride were used as the p-type and n-type layers, respectively. The effects of the deposition method and the thickness of the MoO3layer on the device performance were investigated. The power-conversion efficiency of the optimized hybrid solar cell reached a maximum of 7.08%, which is remarkable considering the novel structure of the dopant-free devices. The light stability of the devices with and without MoO3was also compared: the light stability of the device with MoO3was found to be much better than that of the device without MoO3and with p-i-nSi layers. This was ascribed to the insignificant number of defect sites generated by the nondoping elements, which led to a less contaminated, more compact, and smoother oxide surface, resulting in an increase in the electron lifetime and improved light stability. This work opens up a new direction toward the development of a truly dopant-free device that does not involve the use of toxic gases during fabrication and provides the potential for further enhancement of the efficiency of future dopant-free solar cells.

A single zinc oxide (ZnO) layer deposited by atomic layer deposition (ALD) was employed as a buffer layer on textured fluorine-doped tin oxide (FTO) glass in p-i-n-type hydrogenated amorphous silicon solar cells (a-Si:H SCs). ZnO was deposited between FTO glass and a p-type a-Si:H layer. The device with a 2 nm thick ZnO buffer layer deposition showed the highest cell efficiency as well as increased current density, showing considerable improvement in efficiency. This improvement was attributed to the protection against H2plasma damage during plasma-enhanced chemical vapor deposition, which was confirmed by electrical impedance, conductivity, and optical transmittance measurements.

Herein, we evaluate the effects of the doping concentration and emissive layer (EML) thickness to control the recombination zone (RZ) and exciton density (ED) in blue phosphorescent organic light-emitting diodes (Ph-OLEDs). Varying the doping concentration of the guest molecule iridium-(III)-bis-[(4,6-difluorophenyl)-pyridinato-N,C2'] picolinate (FIrpic) in host materials together with different EML thicknesses induced a change in the RZ and ED and also influenced the quenching of triplet excitons. Increasing the dopant concentration in the 20 nm EML generated a wider RZ and greater ED and induced a blueshift in the electroluminescence spectrum, whereas a redshift in the electroluminescence (EL) spectrum was observed in the case of the 30 nm EML. It is proposed that the micro-cavity effect (around 500 nm), shift of the RZ and ED along with band alignment tactics were operative for improving the performance of the blue Ph-OLEDs.

The structural change with the different location of exciton blocking layer's (EBL) in blue phosphorescent organic light-emitting diodes (PHOLEDs) were investigated, where N,N′-dicarbazolyl-3,5-benzene (mCP) with high triplet bandgap was used as the EBL. The change of recombination zone (RZ) were originated from the different formation of triplet excitons depending on the EBL location between hole/electron transporting layer (HTL/ETL) and emission layer (EML), resulting in the variation of the device performance and generating an optical micro-cavity effect in the electroluminescence (EL) spectrum around 500 nm. The device using the EBL between the HTL and the EML showed the highest device performance due to the good charge balance, avoiding the serious triplet exciton quenching and the reduced micro-cavity effect.

The effects of location and density in triplet exciton formation on the device performance were systematically investigated by the variation of quantum well (QW) structure in blue phosphorescent organic light-emitting diodes. The hole transporting material of 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) as an interlayer was sandwiched between front emitting layer (EML) and rear EML for the construction of QW structure. The variation of the number of the QW unit induces the different exciton formation in recombination zone (RZ) in which the change of exciton density in the QW structure gives rise to the different optical path length and micro-cavity effect of the EL spectra. As the number of the QW unit increases, the corresponding EL spectrum is blue-shifted. It is originated that the exciton density in the front EML increases and the corresponding optical path length is shorten from the EML to the anode. However, the RZ formation in the single EML without QW structure is widened and red-shifted with increasing the EML thickness because the width of the RZ increases toward to the cathode and the length of optical path is expanded from the anode. In addition, the device having 2 units of QW structure in the EML shows the highest device performance of current efficiency, due to the good charge balance and avoiding the serious triplet exciton quenching by the interlayer. The current efficiency of 11.7 cd/A (from 11.7 to 7.3), power efficiency of 5.5 lm/W (from 5.5 to 3.4), and the operation voltage of 9.7 V at 5000 cd/m2were presented for 2 unit QW, while the current efficiency of 9.4 cd/A (from 9.4 to 4.7), power efficiency of 5.9 lm/W (from 5.9 to 1.6) and the operation voltage of 7.1 V at 5000 cd/m2were suggested for 1 unit QW, both showing relatively large efficiency roll-off.

The effects of the electron mobilities and energy levels of different electron transport layer (ETL) materials on the performances were systemically investigated in blue phosphorescent organic light-emitting diodes. The spatial control of recombination zone (RZ) which was accompanied with triplet exciton quenching affected the balance between holes and electrons in the emission layer, resulting in the variations of the device performances. An optical micro-cavity effect in the electroluminescence (EL) spectrum around 500 nm was noticed by employing tris(8-hydroxyquinolinolato)aluminum (Alq3) ETL. This was attributed to the broadening of the emission zone through the emission layer over the ETL, exhibiting the greenish color coordinates. The current efficiency of the device with 3-phenyl-4(10-naphthyl)-5-phenyl-1,2,4-triazole (TAZ) ETL was much higher than that of the same structured device with any other ETL due to better charge balance as well as the suppression of triplet exciton quenching by the narrow RZ with low electron mobility and proper band alignment.

The charge balance mechanism in green fluorescent organic light-emitting diodes is investigated for different electron transport layers (ETLs) and electron mobilities. Carrier accumulation and an increase in the exciton recombination probability are shown to be critical for improving the current and power efficiencies by aligning the bands at the interface between the emitting layer (EML) and ETL. The peak in the electroluminescence (EL) spectra was found to shift slightly in response to changes in the width of the emission zone and reflected the electron mobility of the ETL. Higher electron mobility resulted in a wider recombination zone in the EML that was manifested by a blue-shift of the EL peak.

The mechanisms of charge balance and tuning of the color coordinates in blue phosphorescent organic light-emitting diodes were studied by controlling the emission zone and electroluminescence (EL) spectrum. On the basis of the findings, this paper discusses different hole-injection and mobility factors such as the thickness of the hole injection layer (HIL), the HIL materials, the surface treatment, and the insertion of a buffer layer, which mainly enabled tuning of the color coordinates. The approximately 500-nm-wavelength shoulder peak in the EL spectrum was influenced by the width and location of the emission zone, following the optical micro-cavity effect. Different emission zones were created by different types of hole injection and mobility, which simultaneously enhanced the device efficiency and tuning of the color coordinates.

In this study, we systematically examined the effects of the position of the exciton- blocking layer (EBL) in blue phosphorescent organic light-emitting diodes. The EBL was located either in the front and/or the rear of the emission layer (EML), and its effects to the device performances and electroluminescence spectra were investigated. The width and location of the recombination zone related to the triplet exciton quenching occurred in the devices with/without a front- or rear-EBL resulted in an optical micro-cavity effect in the EL spectrum at approximately 500 nm. The EBLs provided the direct, extra path of charge carriers from the hole transport layer (HTL)/electron transport layer (ETL) to the ETL/HTL through EML, resulting that the device operating voltage did not increase. The device with both front- and rear-placed EBLs exhibited the highest device performance, as triplet exciton quenching did not occur in it at the interface between the HTL/ETL and the EML.

A double layer of gold nano particles (Au-NPs) and amorphous tungsten oxide (a-WO3) was employed as a buffer layer on textured fluorine-tin oxide (FTO) glass in pin-type hydrogenated amorphous silicon solar cells (a-Si:H SCs). Au-NPs of ∼10 nm size were spin coated and a-WO3layer was thermally evaporated between Au-NPs on a FTO glass and hydrogenated amorphous p-type Si layer. a-Si:H SCs with a double buffer layer showed higher efficiency of 7% improvement, 8.059% from a value of 7.530%, and increased current density of 8.3% improvement, 14.212 mA/cm2from a value of 13.120 mA/cm2, originating from the enhancement of electrical interface contact and bandgap alignment, as well as the slight absorption and surface plasmon resonance effect due to Au-NPs on textured FTO glass.

We report on the photovoltaic properties of air-stable inverted organic solar cells in which zinc oxide (ZnO) of varying thicknesses is formed as the electron-transport layer by an atomic layer deposition (ALD) method. The device performance was found to be dependent on the ZnO thickness. Air-stable inverted solar cells with an optimized ZnO thickness reached a power conversion efficiency of 2.91%. This efficiency was found to be comparable to those of conventional organic solar cells. The use of the ZnO electron-transport layer led to improved air stability: the power conversion efficiencies of unencapsulated organic solar cells remained above 80% of their original values even after storage in air for thirty days.

Organic bistable memory devices were demonstrated by applying poly(styrene sulfonate)-doped poly(3,4-ethylene dioxythiopen) (PEDOT:PSS) as a self-organized charge trapping center inside a poly(9,9-dioctylfluorene) (PFO). PEDOT:PSS was introduced as nanoparticles by the chemical surface energy difference between PFO and PEDOT:PSS. The PEDOT:PSS nanoparticles played a role of the charge trapping center and an average on/off ratio around 100 was observed at a reading voltage of −2 V. The combination of PEDOT:PSS nanoparticle and LiF/Al cathode resulted in organic light-emitting bistable devices with a stable bistability and light-emitting performances.

Abstract not Available.

Highly transparent and efficient red phosphorescent inverted top-emitting organic light emitting diodes were investigated by using a surface-modified tungsten oxide (WO3)/silver/WO3(WAW) anode. A thin buckminsterfullerene (C60) dipole layer was introduced for the surface treatment of the WAW anode, and the thickness of the surface-modified WO3was controlled to optimize the WAW anode for hole injection. The optimum thickness of the surface-modified WO3was 5 nm, and the C60 dipole layer further improved the hole injection from the WAW anode to the hole transport layer.