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Improvement in the overall performance of solution-processed organic solar cells based on a ternary heterostructure was realized by means of incorporating small molecules of tris(8-hydroxyquinoline) gallium (Gaq3) or Alq3 electron acceptors. The donor host polymer was α,ω-dihexyl-sexithiophene (DH6T), while the ultimate acceptor was fullerene (PC61BM). The results showed that short circuit current (ISc), open circuit voltage (Voc), and fill factor (FF) of the devices were pronouncedly enhanced by the inclusion of Gaq3 or Alq3. The maximum output power and conversion efficiency of the ternary devices were increased by an order of 5.8 times compared to that of the control devices. These improvements were ascribed to the broadened light absorption, energy levels alignment between the donor-acceptor components, a balanced charge transfer, and increased crystallinity of the devices active layer. The results were ascertained and analyzed by means of UV–Vis, PL, XRD, IV and TEM investigations.

In the present study, poly{4,8-bis[5-(2-ethylhexyl)thiophen-2-yl]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl-alt-3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophene-4,6-diyl} (PTB7-Th) was used to fabricate a novel Al/PTB7-Th/n-Si metal-polymer-semiconductor (MPS) Schottky barrier diode (SBD). The Al/PTB7-Th/n-Si MPS SBD was prepared by employing a spin-coating system and a thermal evaporator for the deposition of PTB7-Th thin film and metal contacts, respectively. The electrical properties of the Al/PTB7-Th/n-Si MPS SBD were investigated by current-voltage method at room temperature in order to extract its main electrical parameters such as ideality factor (n), barrier height (Φb0), series resistance (Rs) and shunt resistance (Rsh). The I–V characteristics revealed nonlinear behavior due to the effect of Rs and ideality factor larger than unity. From the I–V curves, the values of ideality factor and barrier height of the diode were found to be 3.5 and 0.58 eV, respectively. The electrical parameters were verified by Cheung’s and Norde’s functions. The parameters determined by all the three methods were found to be in great agreement. The conduction mechanism of the diode was also studied. The simple and cost effective approach used for the fabrication of Al/PTB7-Th/n-Si MPS SBD demonstrates its potential for being used in the state-of-the-art high-quality electronic and optoelectronic devices.

In this research work, the optical absorption and photo-current characteristics of black grape, strawberry and orange solutions were investigated. The solutions were extracted from fresh fruits and UV-V is spectrophotometer was utilized to record the absorption spectra of the samples. Besides, the photo-current properties were investigated via current-voltage characteristics of the fruit solutions under illumination. The results showed that energy gaps of the fruits are located within the visible spectrum. Energy gap of 1.84eV was found for the black grape, 2.11eV for strawberry and 3.10eV for the orange solution. The broad absorption spectra for black grape and strawberry have proved the fruits capability to harvest solar energy. Additionally, the enhanced photo-current activity of the fruit solutions under light suggested their potential application for the organic and/or dyes solar cells

This research work reports on the optical and photovoltaic performance of dihexyl-sexithiophene (DH6T) doped with various molar percentages of tris-8-hydroxyquinolinate aluminium (Alq3) dissolved in chloroform/hexane cosolvent. Films of DH6T(1-x)Alq3(x) composite have been produced by casting technique aiming at investigating their absorption edge energies (Eabs) and hence identifying the optimum content of Alq3. It was found that by introducing a controlled amount of Alq3, the value of Eabs can be tuned from 2.69 eV to 1.76 eV. An empirical equation was derived to fit the obtained experimental data, by which an optimum Eabs at molar concentration of (x 􀀁 25%) was predicted. Finally, organic solar cells based on the optimum active layer content were fabricated and tested. Comparably, it was observed that the photovoltaic performance of the DH6T:Alq3 based devices is much better than that achieved for the DH6T:PCBM based ones. Efficiency and fill factor for the devices based on DH6T(0.75)Alq3(0.25) active layer were found to be 0.22% and 26.5%, respectively, while those for DH6T:PCBM based devices were about 0.01% and 24%, respectively.

In this work the impedance spectroscopy of α,ω-dihexyl-sexithiophene: methanofullerene; [6,6]-phenyl C61 butyric acid methyl ester (DH6T:PCBM) bulk heterojunction with and without incorporating tris (8-hydroxyquinolinate) gallium (Gaq3) was investigated in the frequency range from 50 Hz to 1 MHz. An electrical circuit was proposed to model the experimental results and to fit the data. The results showed that incorporation of Gaq3 has led to improve the interfaces between DH6T:Gaq3:PCBM moieties. The relaxation time for the Gaq3 incorporated heterojunction was found to be larger than that of the non-incorporated Gaq3 one, which implied a greater possibility for electrons and holes to transport before they relapse or recombine together. The dielectric loss in the Gaq3 incorporated DH6T:PCBM was found to be smaller than that of the non-incorporated one. This was attributed to the improved pathway for charge carriers to transport upon the addition of Gaq3. A peak in the dielectric loss was noticed for 25 % Gaq3 doped DHT:PCBM at about 106 Hz, suggesting the occurrence of dipolar relaxation. The results were analyzed and discussed based on the experimental and modelling investigations.

This work reports on the impact of surface modification on the optical absorption and luminescence response of vacuum deposited tris(8-hydroxyquinoline) gallium (Gaq3) films. This surface modification was achieved by means of thermal treatment under nitrogen gas in the temperature range from 85 o C to 255 o C. The results of field emission scanning electron microscopy (FESEM) and x-ray diffraction (XRD) technique ascertained the formation of amorphous nano-rods along the surface of Gaq3 films. Considerable improvement in the absorption and luminescence characteristics of Gaq3 films was observed upon surface modification, which has been resulted from this treatment process.

This work reports on the impact of surface morphology on the optical absorption of vacuum deposited tris (8-hydroxyquinoline) gallium (Gaq3) films. Morphological investigation was performed for films treated under nitrogen gas in the temperature range from 85 °C to 255 °C. The results of field emission scanning electron microscopy (FESEM) and x-ray diffraction (XRD) technique ascertained the formation of amorphous nanostructures. Considerable modification in the absorption behaviour of Gaq3 films was observed upon morphological changes. The results of these modifications were ascribed to the impact of morphological variations among the surface of Gaq3 films.

In this research article, the influence of environment temperature on the performance of the organic bulk heterojunction organic solar cells has been investigated. We describe the effect of ambient temperature on the efficiency of poly-[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta-[2,1-b;3,4-b′]dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) and [6, 6]-phenylC71-butyric-acid-methyl-ester (PC71BM)-based bulk heterojunction (BHJ) organic solar cells. The current–voltage characteristics of the ITO/PEDOT:PSS/PCPDTBT:PC71BM/Al solar cells are recorded in the temperature range of 25–60 °C under 100 mW/cm2 solar irradiation. The short-circuit current (J sc) of the solar cells increased from 4.28 to 9.23 mAcm−2 when the temperature elevated from 25 to 55 °C. However, the open-circuit voltage (V oc) and fill factor (FF) of the cells almost remained unchanged over the whole investigated temperature range. The values of V oc and FF are found to be 0.58 ± 01 and 0.60 ± 0.12 V, respectively. The results clearly indicate that the maximum efficiency of the ITO/PEDOT:PSS/PCPDTBT:PC71BM/Al solar cells can be achieved in the range of 52–58 °C. This publication was made possible by PDRA Grant No. PDRA1-0117-14109 from the Qatar National Research Fund (a member of Qatar Foundation). The findings achieved herein are solely the responsibility of the authors. Scopus

This work reports the optical and morphological modifications in vacuum deposited Gaq3 films upon thermal annealing. The annealing process has been carried out under flowing nitrogen gas for 10 min. It was noticed from the results that at 235 °C a broad absorption spectrum and increased photoluminescence to five times stronger than that of pristine film was achieved. Scanning electron microscopy and X-ray diffraction techniques ascertained morphological changes towards the formation of amorphous nanorods. The improvement in optical properties of Gaq3 films was found to be resulted from this morphological modification. The nanostructure formation was seen to be a viable method to enhance the morpho-optical properties of Gaq3 films, making Gaq3 a promising candidate for the application in organic electronics technology.

In this work we investigate the impact of the dopant salt on the optical constants of PVA:NaNO3 composite system. Samples with various NaNO3 dopant contents were prepared by casting technique using distilled water as a solvent. The refractive index (n), extinction coefficient (k), dielectric constants (ɛ r and ɛ i ) and complex optical conductivity (σ*) for the systems have been investigated. Through applying Tauc’s equation and Wemple–DiDomenico (W–D) model, the optical energy gap (E g ) and Urbach tail energies (E u ) were correlated and analyzed. The exponent value (n) in Tauc’s equation has been calculated numerically and it was utilized to understand the nature of electronic transitions. The change in the refractive index from 1.14 for pure PVA to 2.25 for 12 % doped PVA was noticed, indicating the presence of few interactions between photon and electrons. This doping effect has considerably increased the real dielectric constant from 1.30 for pure PVA to 5.10 for 12 % doped PVA. The results showed that dispersion region of refractive index obeyed the W–D model.

In this work the optical response, spectroscopic behaviour, and optoelectronic properties of solution and solid state composite systems based on α,ω-dihexylsexithiophene/tris(8-hydroxyquinolinate) gallium (DH6T/Gaq3) are studied upon the incorporation of different molar percentages of Gaq3. UV–vis, PL, FTIR spectrophotometers and SEM technique were utilized to perform the investigations. The results showed a reduced energy band (Eg) (from 2.33 eV to 1.83 eV) and a broadened absorption spectrum for the blend system when 29.8% molar of Gaq3 was incorporated. These were attributed to the enhanced intermolecular interactions that are brought about by the increased strength of π − π overlap between the molecular moieties. A mathematical formula was developed to interpret the non-monotonic change occurred in Eg, while numerical calculations have been made to assign the type and nature of the electronic transitions governing the spectroscopic behaviour of the system. The results were elaborated and comprehensively discussed in terms of the exciton generation, energy band theory, molecular interactions, and spatial geometry.

In this study we report the optical, spectroscopic, and structural properties of vacuum deposited tris (8-hydroxyquinolinate) gallium film upon thermal annealing in the temperature range from 85 °C to 255 °C under a flowing nitrogen gas for 10 min. The optical UV–vis–NIR and luminescence spectroscopy measurements were performed to estimate the absorption bands, optical energy gap ( E g ), and photoluminescence (PL) of the films. Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) techniques were used to probe the spectroscopic and structural nature of the films. We show that, by annealing the films from 85 °C to 235 °C, it is possible to achieve an enhanced absorption and increased photoluminescence to five times stronger than that of the pristine film. The PL quenching at 255 °C was attributed to the presence of plainer chains allow easy going for excitons to a long distance due to the crystalline region formation of α-Gaq3 polymorph. The reduction in E g and infrared absorption bands upon annealing were referred to the enhancement in π–π interchain interaction and conformational changes by re-arrangement of the Gaq3 quinolinate ligands, respectively. Stokes shift for the films were observed and calculated. From the differential scanning calorimetry, DSC measurements, higher glass transition temperature was observed for Gaq3 ( T g = 182 °C) compared to that of Alq3 ( T g = 173 °C), which suggests the existence of stronger dipolar interaction in Gaq3 due to the Ga 3+ cation effect, in comparison to that of Alq3.

Organic Solar Cells based on α, ω- dihexyl-sexithiophene (DH6T) and [6,6]-phenyl C 61 -butyric acid methyl ester (PCBM) were fabricated and characterized. The photovoltaic performance of three different architectural structures namely DH6T/PCBM (bilayer), PEDOT:PSS/DH6T/PCBM (bilayer) and PEDOT:PSS/DH6T:PCBM (1:1 bulk heterojunction) were investigated and discussed through the current and power density–voltage, ( J–V ) and ( P–V ) characteristics of the devices under 100 mW/cm 2 white light illumination in air. The results show higher performance for the bulk heterojunction devices with enhanced power conversion efficiency by 150% of that obtained in the PEDOT:PSS/DH6T/PCBM bilayer devices. This is ascribed to the red shift obtained in the absorption spectra and better donor/acceptor proximity of DH6T:PCBM bulk heterojunction films compared to those of the DH6T/PCBM bilayers.

For the purpose of investigating electro-molecular absorption bands, energy gaps, E g and molecular energy levels (ionization potential, IP and electron affinity, EA ) of tris (8-hydroxyquinolinate) gallium and aluminum, spectral analysis in conjunction with electrochemical measurements was carried out. UV–Vis–NIR and FTIR spectroscopic measurements were used to assign the electronic and molecular absorption bands in both of the materials. The XRD and scanning electronic microscopy (SEM) technique showed the amorphous nature. From the recorded data of cyclic voltammetry (CV) and materials absorption coefficient, HOMO, LUMO energy levels and energy gaps for Gaq3 and Alq3 were calculated. A bit smaller value of energy gap for Gaq3 (2.80 eV) compared to that of Alq3 (2.86 eV) has been ascribed to the differences in electronic configuration and coordinated bond lengths related to the central metal atom with respect to the quinolinate ligands. A higher value of HOMO energy level for the Alq3 ( IP = 6.3 eV) revealed the need of higher potentials to oxidize its molecules comparing to that of Gaq3 ( IP = 5.8 eV). It was observed that cationic metals have a direct effect on the physical and chemical behaviors of such organometallic materials that can be exploited to be used in tuning their properties to match the desired application in OSC and/or OLED technologies.