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Quasi‐2D‐layered perovskites have more exotic optical properties than their 3D halide perovskites congener, such as prominent excitonic features, higher photoluminescence (PL) yield, and composition‐induced energy transfer among different phases. However, there are known challenges in quasi‐2D perovskite where by default one gets a mixture of various phases (n = 1, 2, 3….3D) in one composition. Energy transfer processes occur among various phases, and optimization is needed to ensure one can get the best optical properties by targeting optimal phase purity. Herein, a detailed analysis of structural and optical properties of different perovskites (2D perovskite, quasi‐2D perovskite, and 3D perovskite) of (PEA)2(FAPbBr3)n−1PbBr4 series is done. The n = 3 composition with the least phase impurity is prepared, which provides a higher PL emission intensity than members of this series. Hence, the n = 3 composition (emissive layer) based perovskite light‐emitting diode (PeLED) is fabricated. Poly(9‐vinyl carbazole) (PVK) as an additional hole‐injection layer with poly(3,4‐ethylene dioxythiophene) polystyrene sulfonate (PEDOT:PSS) helps to suppress (1) the leakage current (effective blocking of electrons) and (2) the non‐radiative channels at the interface. Optimized thickness of emissive layer in PeLED (100 nm) gives a luminance efficiency of 15.4 cd A−1 and external quantum efficiency (EQE) of 4.32%.

A study of hybrid light-emitting diodes (HyLEDs) fabricated with and without solution-processible Cs 2 CO 3 and Ba(OH) 2 inorganic interlayers is presented. The interlayers are deposited between a zinc oxide electron-injection layer and a fl uorescent emissive polymer poly(9-dioctyl fl uorine‐alt-benzothiadiazole) (F8BT) layer, with a thermally evaporated MoO 3 /Au layer used as top anode contact. In comparison to Cs 2 CO 3 , the Ba(OH) 2 interlayer shows improved charge carrier balance in bipolar devices and reduced exciton quenching in photoluminance studies at the ZnO/Ba(OH) 2 /F8BT interface compared to the Cs 2 CO 3 interlayer. A luminance effi ciency of ≈ 28 cd A − 1 (external quantum effi ciency (EQE) ≈ 9%) is achieved for ≈ 1.2 μ m thick single F8BT layer based HyLEDs. Enhanced out-coupling with the aid of a hemispherical lens allows further effi ciency improvement by a factor of 1.7, increasing the luminance effi ciency to ≈ 47cd A − 1 , corresponding to an EQE of 15%. The photovoltaic response of these structures is also studied to gain an insight into the effects of interfacial properties on the photoinduced charge generation and backrecombination, which reveal that Ba(OH) 2 acts as better hole blocking layer than the Cs 2 CO 3 interlayer.

Polymer/organic optoelectronic devices have drawn the attention of both the academic and industrial research communities due to the potential for a low-cost, large-area, solution-processable technology alternative to conventional inorganic optoelectronics. Issues related to the stability and degradation of the organic/polymer-based optoelectronics are hampering the progress in the field. The use of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT : PSS) as the anode and reactive metals as the cathode, as well as the degradation of organic semiconductors in ambient atmosphere, are some of the stability issues to be addressed. To resolve these issues, in the past decade, there has been a growing interest in research of hybrid optoelectronic devices which employ metal oxides as air-stable charge injecting/extracting layers that sandwich the photo-responsive organic active layer and protect it from the ambient oxygen and moisture and prevent photo-oxidation by absorbing UV light. Herein, we review the recent advances made in hybrid optoelectronics and discuss the tremendous potential of these devices.

Single-layer polymer light-emitting field-effect transistors (LEFETs) that yield EQEs of >8% and luminance efficiencies >28 cd A(-1) are demonstrated. These values are the highest reported for LEFETs and amongst the highest values for fluorescent OLEDs. Due to the electrostatics of the ambipolar LEFET channel, LEFETs provide an inherent advantage over OLEDs in terms of minimizing exciton-polaron quenching.

This work investigates the composition and morphology of films of poly(3-hexylthiophene) (P3HT), polyfluorene co-polymer poly((9,9-dioctylfluorene)-2,7-diyl-alt-[4,7-bis(3-hexylthien-5-yl)-2,1,3-benzothiadiazole]-2′,2″-diyl) (F8TBT) and blends thereof that are used in efficient all-polymer solar cells. Ultraviolet photoemission spectroscopy (UPS) and X-ray photoemission spectroscopy (XPS) studies on thin polymer and blend films on ZnO substrates reveal the existence of a 1–2 nm thick P3HT layer at the top surface of the blend films. XPS depth profiling studies reveal a density wave (λ ≈ 70 nm) originating from the air interface. As no preferential accumulation is observed at the bottom interface with ZnO, the composition at this interface is consistent with the original composition of the blend solution prior to spin-coating. The morphology of this buried interface was studied by means of atomic force microscopy (AFM) and revealed that upon annealing the average domain size increases slightly (from 27 nm to 40 nm). It is observed that the photovoltaic performance of such inverted hybrid device improves upon annealing, however we believe this to mostly be a result of increased crystallinity in the P3HT domains leading to improved charge transport in the device, rather than changes in the blend phase separation.

A study of an efficient blue light-emitting diode based on a fluorescent aryl polyfluorene (aryl-F8) homopolymer in an inverted device architecture is presented, with ZnO and MoO3 as electron- and hole-injecting electrodes, respectively. Charge-carrier balance and color purity in these structures are achieved by incorporating poly(9,9-dioctylfluorene-co-N-(4-butylphenyl)-diphenylamine (TFB) into aryl-F8. TFB is known to be a hole-transporting material but it is found to act as a hole trap on mixing with aryl-F8. Luminance efficiency of ≈6 cd A−1 and external quantum efficiency (EQE) of 3.1% are obtained by adding a small amount (0.5% by weight) of TFB into aryl-F8. Study of charge injection and transport in the single-carrier devices shows that the addition of a small fraction of hole traps is necessary for charge-carrier balance. Optical studies using UV–vis and fluorescence spectroscopic measurements, photoluminescence quantum yield, and fluorescence decay time measurements indicate that TFB does not affect the optical properties of the aryl-F8, which is the emitting material in these devices. Luminance efficiency of up to ≈11 cd A−1 and EQE values of 5.7% are achieved in these structures with the aid of improved out-coupling using index-matched hemispheres.

Here, the use of metal oxide layers both for charge transport and injection into an emissive semiconducting polymer and also for the control of the in-plane waveguided optical modes in light-emitting diodes (LEDs) is reported. The high refractive index of zinc oxide is used to confine these modes away from the absorbing electrodes, and include a nano-imprinted grating in the polymer layer to introduce distributed feedback and enhance optical out-coupling. These structures show a large increase in the luminescence efficiency over conventional devices, with photoluminescence efficiency increased by up to 45%. Furthermore, optically-pumped lasing in hybrid oxide polymer LEDs is demonstrated. A tuneable lasing emission is also obtained in a single device structure by employing a graduated thickness of a zinc oxide inter-layer. This demonstrates the scope for using such architectures to improve the external efficiency of organic semiconductor LEDs, and opens new possibilities for the realization of polymer injection lasers. ©2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim.

A comprehensive study of various metal oxides in mesoporous and compact forms for electron injection in highly luminescent composite oxide-polymer light emitting diodes (COPLED) was presented. An improved performance with higher luminance and lower turn on voltage without O2 plasma treatment of the ITO prior to metal-oxide deposition is observed. It is found that the compact TiO2 performs considerably better than the mesoporous TiO2 and that the compact ZnO electron injection layer performs better than mesoporous and compact anatase. The higher current densities are due to leakage current through metal-oxide compact layers, and improvement of this deposition is found to increase the performance. Introducing a photonic structure into the metal oxide layers is found to enhance the optical out-coupling and electroluminescance efficiency.

A method for determining the electron/hole transport length scale of model semiconducting polymer systems by scanning a narrow-light probe beam over the nonoverlapping anode/cathode region in asymmetric sandwich device structures is presented (see figure). Electron versus hole collection efficacy, and disorder and spatial anisotropy in the electrical transport parameters can be estimated.

It is demonstrated that the energy transfer from low- conjugated (LC) poly[2-methoxy-5-(2-ethylhexyloxy)-1,4- phenylene vinylene] (MEHPPV) to high-conjugated (HC) MEHPPV, coupled with significant electron transfer from HC- MEHPPV to an acceptor species, offers a viable route for an efficient photodiode over a wide spectral range. An enhanced incident-photon-tocurrent conversion efficiency (IPCE) of 19% over a wide spectral range and a power- onversion efficiency $(\eta_P)$ of 1% (under monochromatic illumination at $\lambda \sim 530$ nm and a power density of ca. $1 mWcm^{-2})$ are achieved in a ternary polymer-blend film that consists of HC-MEHPPV (low bandgap), LC-MEHPPV (high bandgap), and an acceptor polymer, cyanoPPV (CNPPV), in an optimized ratio. The decisive role of the morphology that emerges during phase separation in the polymer blend is demonstrated by wide-field photocurrent imaging.