SCLC Measurements Research Articles

Perovskite single crystal SCLC measurement prediction using a machine learning model

Organic–inorganic halide perovskite single crystal SCLC measurement prediction using a machine learning model.

Correction: Perovskite single crystal SCLC measurement prediction using a machine learning model

Correction for ‘Perovskite single crystal SCLC measurement prediction using a machine learning model’ by Sarvani Jowhar Khanam et al., J. Mater. Chem. C, 2024, https://doi.org/10.1039/D4TC01987C.

Effects of rubidium substitution of Cs2−xRbxAgBiBr6 double halide perovskites on resistive switching characteristics for memory applications

Cation substitution technique in halide perovskites (HPs) is one of the famous schemes to enhance the characteristics of HPs-based electronic and optoelectronic devices. Here, we fabricated rubidium (Rb) substituted inorganic double halide perovskites (HPs) Cs2−xRbxAgBiBr6 (x = 0, 0.05, 0.1, 0.2, and 0.3) film-based resistive switching (RS) devices and investigated effects of Rb cation substitution on characteristics of RS devices. Grain sizes of the formed Cs2−xRbxAgBiBr6 films gradually increased as increase of Rb contents in the precursor. All of the fabricated RS devices demonstrated non-volatile bipolar RS behavior, device with the Rb content x = 0.1 showed a particularly high on/off ratio (9.29 × 102) of about 30 times greater than pristine Cs2AgBiBr6-based ones (3.09 × 10). In addition, it has been shown that an appropriate amount of Rb substitution at the level of x = 0.1 can effectively prevent the appearance of other crystalline phases at high humidity condition of > 80 %. Through various analytical techniques including SEM, XPS, and SCLC measurement, it was confirmed that an enlargement in grain size resulting in a decrease in defects such as Br vacancies in the fabricated film can lead to an increase in resistance at a high resistance state (HRS) and high on/off resistance ratio. This study provides a facile and feasible way to enhance performances of HPs-based RS devices for practical electronic memory applications.

Role of peripheral substitution on electronics and self-assembly of discotic semiconductors: The case of diazatruxenone

In this paper we present two sets of diazatruxenones functionalized at the 3,8 or 2,7 positions with two phenyl rings substituted at the para positions with groups of different electronic nature. With the aim to shed light on the role of the positional isomeric effect and of the electronic nature of the attached peripheral substituents on the final properties of these systems, we have performed a joint experimental and theoretical investigation linking thermal analysis, UV–Vis spectroscopy, electrochemistry and SCLC measurements with DFT calculations. The donor–acceptor character of these molecules not only confers them an interesting amphoteric redox behaviour but also creates a significant in-plane dipole moment. We have found that the different functionalization has only a slight impact on the electronic properties of these systems but exerts a significant influence on the strength and directionality of their dipole moment with strong implications in their self-assembly. Particularly, derivatives functionalized with electron acceptors, present the highest dipole moments within the series and form stable columnar mesophases, probably driven by the antiparallel dipole–dipole arrangement of neighbouring molecules. DFT calculations confirms that cofacially stacked dimers with their dipoles opposed allow for efficient electronic couplings helping to rationalize the favourable hole mobilities determined for the 3,8-disubstituted diazatruxenones with electron-acceptor groups by means of the space charge–limited current technique.

Study of step annealing method and the effect on optical, structural, morphological and transport properties of CH3NH3PbI3

Thermal annealing is used as a post-deposition processing method for the formation of solid-state organic-inorganic perovskite film of required phase by removing the remnant solvent in as coated film. In the present work, we have studied temperature, time and the application of giving a temperature step for thermal-annealing process. To provide temperature step heating treatment was given to the spin coated film in two consecutive steps; initially heating at lower temperature followed by at 100 °C for 30 min. We show that initial lower temperature annealing step improves crystallite size by retarding crystalline growth due to slower solvent evaporation and obtain improved absorption, phase, surface coverage and mobility. However, if this lower temperature step is not sufficient to step up the formation of desired phase, the second step of higher temperature annealing is also not able to form perovskite phase. This study is supported by studies like UV–visible absorption spectroscopy, Raman spectroscopy, X-ray diffraction, scanning electron microscopy, SCLC measurements etc.

Polyaniline polymer-modified ZnO electron transport material for high-performance planar perovskite solar cells

In this study, an efficient strategy is used to prepare perovskite photoactive layer with superb optoelectronic merits by utilizing polyaniline polymer as an efficient additive to improve perovskite quality. As a result, we prove that the small content of polyaniline (PANI) provides not only suppresses the perovskite defects and lead iodide but also produces a passivation impact. By regarding using macromolecular phases with long chain polymers, the generation of a PANI-perovskite cross-linking is possible. The cross-linking acts to bridge the perovskite crystals, mitigating carrier trapping by grain boundaries and achieving remarkable air stability against humid, which has not been obtainable with tiny molecules defect passivating materials. Also, PANI promoted the development of Lewis base adduct with the perovskite precursor, which, maximized the activation energy for nucleation and growth of the perovskite phase. Therefore, the perovskite layer with optimized PANI additive showed higher crystallinity in (110) crystal plane. After PANI addition, the perovskite grains found to be enlarged from 350 nm to 620 nm. Also, the PSCs with PANI showed suppressed luminescence effect, which indicates lower recombination rates. The SCLC measurements revealed that the PANI additive improving the interfacial contact between the ZnO and perovskite due to reduction the trapped density from 1.78 × 1016 cm-3 to 2.46 × 1015. Consequently, the champion cell yields an efficiency of 17.39% for 4% polyaniline doped electron transport material with negligible hysteresis. This reduces PSC instability generating a device that retained 93% of its original performance after 600 h maintaining in air conditions without any encapsulation.

Processing Strategies for an Organic Photovoltaic Module with over 10% Efficiency

Summary A series of readily accessible and scalable benzo[1,2-b:4,5-b′]dithiophene (BDT)-2,5-dithienyl-thieno[3,4-c]pyrrole-4,6-dione (TPD-T2)-based donor polymers are utilized in organic photovoltaic (OPV) cells blended with the non-fullerene acceptor IT-4F. All polymers readily dissolve in chlorine-free solvents such as xylene, and the corresponding photoactive blend films can be processed in ambient from this solvent to fabricate cells with power conversion efficiencies (PCEs) >12%–14%. Furthermore, the blend processing and OPV metrics are remarkably insensitive to the processing methodology (spin coating versus blade coating), processing solvent, polymer molecular mass and dispersity index, and the results were rationalized by UV-vis, PL, fsTA, AFM, TEM, GIWAXS, and SCLC measurements. These properties enable the first OPV modules, processed in ambient from a benign solvent, with a certified PCE of 10.1% for an area of 20.4 cm2 and >7% after light soaking. The same module also delivers a power of ∼40 μW/cm2 (PCE ∼22%) under indoor lighting.

Stable Postfullerene Solar Cells via Direct C–H Arylation Polymerization. Morphology–Performance Relationships

The scope of the environmentally benign direct C–H arylation polymerization (DARP) process is validated and significantly extended in the synthesis of a high-performance benzodithiophene-based copolymer series, PBDT(Ar)-FTTE, with previously untested and systematically varied heteroaryl (Ar) substituents. Bulk-heterojunction (BHJ) polymer solar cells (PSCs) containing the high-performance nonfullerene acceptor (NFA) ITIC-Th and DARP-derived donors are fabricated and evaluated, yielding PCEs as high as 8%. The relationships between Ar-sensitive copolymer structure, BHJ morphology, and PSC performance are elucidated through in-depth characterization of structural order, phase separation, and charge transport using SCLC, AFM, GIWAXS, R-SoXS, and NEXAFS measurements, which conclusively demonstrate the important effects of Ar-tunable, dimensionally smaller, and well-blended copolymer domains for maximum PSC performance. Smaller BHJ copolymer domains having greater ITIC-Th miscibility definitively correlate wit...

Alkyl‐Chain‐Separated Triphenybenzene ‐ Carbazole Conjugates and their Derived Polymers: Candidates for Sensory, Electrical and Optical Materials

AbstractFour new triphenylbenzene based carbazoles (THPBCz4, THPBCz6, THPBCz8 and THPBCz10) and polycarbazoles (polyTHPBCz4, polyTHPBCz6, polyTHPBCz8 and polyTHPBCz10), have been synthesized. Photoluminescence spectra of the monomers in dichloromethane exhibit two intense bands at 353 and 369 nm. Two additional bands (410 and 435 nm) are also observed due to intermolecular interactions. These bands are more intense in the case of thin films, indicating stronger π‐π stacking interactions in the solid state. Due to the extended π‐conjugation, the polycarbazoles display two main emission bands (495 and 520 nm) which are red shifted as compared to the monocarbazoles. Due to the presence of emissive platforms such as triarylbenzene and carbazole, both monomers and polymers, function as efficient sensors for the detection of polynitroaromatic analytes (PA, DNT, p‐DNB and m‐DNB). The electrochemically polymerized carbazole derivatives showed maximum capacitance of 41 F/g for polyTHPBCz6. The SCLC measurement reveals a maximum mobility of 6 x 10−6 cm2/Vs for polyTHPBCz4 that showed better packing due to flexible alkyl chains that connect the conjugated moieties.

Morphological engineering via processing additive in thin film bulk-heterojunction photovoltaic cells: A systematic understanding of crystal size and charge transport

In this research, organic photovoltaic devices based on bulk-heterojunction (BHJ) from Poly(3-hexylthiophene-2,5-diyl) (P3HT)/[6,6]-phenyl C71 butyric acid methyl ester (PC71BM) were successfully fabricated to determine the optimization of solvent additive of 1,8-diiodooctane (DIO). The BHJ devices with DIO show improved short circuit current (JSC) correlated to the improved device performance, since the DIO in P3HT:PC71BM BHJ affects the morphology in terms of the surface roughness and crystal size. Furthermore, the DIO contributes to the enhanced charge carrier transport of the BHJ device, because the decreased fluorescence and increased hole mobility as found through Raman spectra analysis and SCLC measurement, respectively. The device with optimized concentration (1 vol %) of DIO accomplishes 5% improved photovoltaic performance due to the favorable structural property and enhanced carrier mobility.

Fusion of perylene bisimides and hexaazatriphenylene into a star-shaped ladder conjugated n-type semiconductor

Novel n-type star-shaped molecule TriPBI containing a HAT core and three fused PBI “arms” was synthesized and characterized. The n-type charge carrier mobility as high as 3.34 × 10−3 cm2 V−1 s−1 of TriPBI is evaluated by SCLC measurements, which is considerably higher than 8.71 × 10−5 cm2 V−1 s−1 of the PBI monomer.

The Investigation of Two Different Types of Multiple-Quantum-Well Structure on Fluorescent White Organic Light Emitting Devices

To study the effect of multiple-quantum-well (MQW) structure on emission characteristics of white organic light-emitting diodes (WOLEDs), we fabricate trapping-type and blocking-type MQWs by inserting C545T (green dye) and TPBi, respectively, into hole transport NPB layer (ITO/CuPc/NPB/MADN:rubrene/TPBi/LiF/Al). Bright efficient and stable fluorescent white emission was obtained for the OLED with 2 trapping-type MQWs formed with C545T (thickness: 2 nm). The device current and power efficiency were greatly raised 36% (7.55 cd/A, 4.36 lm/w) relative to that of reference device (5.44 cd/A, 3.40 lm/w). Furthermore, the improvement remained even beyond the roll-off effect caused by high current density. However, the blocking-type MQW structure was difficult to optimize due to too intense blocking effect of TPBi layer. The mechanistic differences between trapping- and blocking-type MQW structures were elucidated using hole-only device and SCLC measurements. The experimental results show that trapping-type MQW structure manipulates hole transport effectively to improve charges balance which is essential in enhancing device performance, making it applicable for facile fabrication of efficient OLEDs.

A High‐Mobility Low‐Bandgap Copolymer for Efficient Solar Cells

AbstractA new high‐mobility low‐bandgap polymer, PBDT‐DODTBT, based on benzodithiophene and 5,6‐bis(octyloxy)‐4,7‐di(thiophen‐2‐yl)benzothiadiazole has been synthesized through a standard Stille coupling reaction. The polymer is soluble in common organic solvents, such as chloroform, tetrahydrofuran, and chlorobenzene and has excellent film forming properties. Preliminary studies of the copolymer showed the charge mobility as high as 7.15 × 10−3 cm2 · V−1 · s−1 from SCLC measurement. Initial photovoltaic cells based on the composite structure of ITO/PEDOT:PSS/PBDT‐DODTBT:αPC71BM (1:2)/Ca/Al showed an open‐circuit voltage of 0.76 V, a power conversion efficiency of 4.02%, and a short‐circuit current of 8.96 mA · cm−2. magnified image

Ohmic contact probed by dark injection space-charge-limited current measurements

The authors demonstrate through dark injection space-charge-limited current (DI-SCLC) and trap-free SCLC measurements that an indium tin oxide (ITO)/buckminsterfullerene (C60) electrode can form a quasi-Ohmic contact with N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl) benzidine (NPB). The DI-SCLC results show a clear peak current along with a shift of the peak position as the field intensity varies, implying an Ohmic (or quasi-Ohmic) contact. A theoretical simulation of the SCLC also shows that ITO/C60 forms an Ohmic contact with NPB when the electric field intensity is higher than 30 kV/cm. The Ohmic contact makes it possible to estimate the NPB hole mobility through the use of both DI-SCLC and trap-free SCLC analysis.

Study of electrical properties of glassy Se100- xTexalloys

Temperature and frequency dependence of a.c. conductivity have been studied in glassy Se100- x Te x(x = 10, 20 and 30) over different range of temperatures and frequencies. An agreement between experimental and theoretical results suggests that the a.c. conductivity behaviour of selenium-tellurium system (Se100- xTex)can be successfully explained by correlated barrier hopping (CBH) model. The density of defect states has been determined using this model for all the glassy alloys. The results show that bipolaron hopping dominates over single-polaron hopping in this glassy system. This is explained in terms of lower values of the maximum barrier height for single-polaron hopping. The values of density of charged defect states increase with increase in Te concentration. This is in agreement with our previous results obtained from SCLC measurements.

Identification of polymorphs of pentacene

Pentacene crystallizes in a layered structure with a herringbone arrangement within the layers. The electronic properties depend strongly on the stacking of the molecules within the layers [J. Phys. Chem. B. 106 (2002) 8288]. We have synthesized four different polymorphs of pentacene, identified by their layer periodicity, d(0 0 1): 14.1, 14.4, 15.0 and 15.4 A ̊ . Single crystals commonly adopt the 14.1 A ̊ structure, whereas all four polymorphs can be synthesized in thin film form, depending on growth conditions. We have identified part of the unit cell parameters of these polymorphs by X-ray and electron diffraction (ED). The 15.0 and 15.4 A ̊ polymorphs transform at elevated temperature to the 14.1 and 14.4 A ̊ polymorphs, respectively. Using SCLC measurements, we determined the mobility of the 14.1 A ̊ polymorph to be 0.2 cm 2/V s at room temperature.

SCLC Measurements in Nickel Phthalocyanine Thin Films

Sandwich structures of Au/NiPc/Au were fabricated by sequential vacuum thermal sublimation onto borosilicate glass substrates. dc electrical measurements were performed for several NiPc thin films of different thickness in the range (d = 0.25-1.09 μm). The relative permittivity was measured at a low frequency of 100 Hz, yielding a value of er = 2.74. This value is considerably lower in comparison with previously published data for various phthalocyanine materials. Current density-voltage characteristics at room temperature reveal an Ohmic conduction in the lower voltage range, followed by SCLC in the higher range, where the latter was found to be controlled by an exponential trap distribution. The plot of current density versus thickness provides further evidence of this effect. The results are analyzed in terms of exponential trap distribution yielding the following values: The temperature parameter characterizing the exponential trap distribution Tt = 1165 K, the concentration of thermally generated holes p0 = 1.40 × 1016 m-3, trap concentration per unit energy range P0 = 4.71 × 1043 J-1 m-3 and total concentration of traps Nt(e) = 7.57 × 1023 m

Electrical transport in porous silicon from improved complex impedance analysis

AbstractAn improved analysis of the electrical transport parameters in meso-porous silicon is presented. Our approach is based on a separate contribution of the crystallites and their interconnections to the total impedance of meso-porous silicon layers. Meso-porous silicon morphology exhibits a columnar structure without quantum confinement. The electrical conduction is thus, partially due to the bulk conductivity within continuous paths of crystallites. The samples were realized on 0.02ω-cm p-type Si substrates. Porous silicon layers of 100µm of thickness and 50% of porosity were inserted in Al/SiO2/porous-Si/Si structures. Their electronic transport parameters were determined using complex impedance measurements. A frequency range of 102 - 107 Hz was used allowing an accurate determination of the impedance components. Combined with thermal stimulation, theses measurements provide a powerful tool for the interpretation of basic properties such as the carriers density in the crystallites and the trapping mechanisms. Our results were interpreted in terms of free carriers conduction in partially compensated crystallites prevailing at low frequencies. At high frequencies (above 10 kHz), the electrical conductivity is mainly controlled by hopping transport on localized states in the chaotic porous structure. Finally, the free carriers mobility, evaluated from SCLC measurement is discussed.

Electronic density of states in highly tetrahedral amorphous carbon

Highly tetrahedral amorphous carbon (ta-C) films and its hydrogenated form (ta-C:H) have been deposited using a filtered cathodic arc. In this paper, the optical and electronic band-gaps of amorphous diamond and its hydrogenated form ta-C:H, are shown to be in the range 2 eV. The H content of ta-C:H is found to be about 3 at.% using elastic recoil detection analysis (ERDA) and electron energy loss spectroscopy (EELS) is used to show that ta-C:H does keep its tetrahedral structure. Both materials are found to be stable at temperatures up to 1000 K. The room temperature conductivity of 10 −7−10 −8 Ω −1 cm −1 is shown to be thermally activated, with activation energies in the range 0.2–0.3 eV. A detailed study made from the current-voltage characteristics of ta-C/ p-Si heterojunctions shows that current flow is space-charge limited (SCLC) and influenced by bulk traps. The density of states profile, N( fE), in the region of the quasi-Fermi level is calculated using the differential method and found to be of the order 10 18 cm −13 eV −1. Optical absorption data is coupled with the electrical results to confirm that the valence band density of states is of the order 10 21 cm −13 eV −1. It is also shown that there is a reduction of nearly one order of magnitude in the N( E) at the quasi-Fermi level upon hydrogenation. SCLC measurements are complemented with surface admittance measurements (SAM) which yield a value of 10 11 cm −2 eV −1 for the interfacial density of states at the ta-C/ p-Si junction. A decrease in N ss is also observed at the ta-C:H/ p-Si interface in agreement with the SCLC results.

Space Charge Limited Current in A-Si:H Devices Using High Electric Fields

ABSTRACTSpace Charge Limited Current (SCLC) measurements are used to obtain the density of gap states of intrinsic a-Si:H. If an electron is trapped by a positively charged defect, then the electron can be released by a high electric field which disturbs the SCLC measurement. A correction for this effect, which is called Poole-Frenkel emission, in SCLC measurements is derived and used to analyze current-voltage measurements performed on n-i-n a-Si:H devices. It is shown that the Poole-Frenkel emission is absent, and that this is in accordance with the contemporary models for the gap states in a-Si:H.We also studied the characteristic temperature which is based on the concept that the distribution of gap states is exponential, and concluded that this distribution is not exponential.