Search

Nowadays, the main barriers facing organic solar cells (OSCs) from being commercialized and widely applied are their weak thermal stability and reproducibility problems. To tackle these problems, researchers usually consider various strategies which include modification in the devices architectural design, utilizing low energy gap materials, functionalizing their active layers, and the use of various optimization procedures. In this research work, we are specifically focused on the utilization of a small molecular organometallic, tris(hydroxyquinoline)gallium (Gaq3), as a secondary acceptor dopant, aiming at improving thermal stability, and reproducibility of OSCs. All-solution processed technique with the help of spin coater was used to deposit the active layer of the devices. Results showed that the addition of 29% molar fraction of Gaq3 into the devices active layer has considerably improved the thermal stability, photo-absorption, and reproducibly of the solar cells thanks to the excellent thermal stability and electron mobility of Gaq3 molecules. Our devices based on DH6T: PCBM:Gaq3 performed highest stable performance at 180°C, implying higher thermal stability compared to that of the reported P3HT: PCBM:F8BT and PTB7:PCBM: F8BT based solar cells. In spite of improved reproducibility, the efficiency of the devices was increased by 5.8 times compared to that of the control ones.

In this work, the impacts of thermal treatment on the optical, structural and photovoltaic properties of ternary organic solar cells based on DH6T:Gaq3:PC61BM are investigated in the temperature range from 413 to 493 K. The addition of Gaq3 organometallic material as a secondary acceptor is to boost the performance and reproducibility of the devices. The results showed an increased crystallinity, improved photo-absorption and decreased photoluminescence response for the active layers upon annealing to up to 453 K, which was accompanied by the enhancement in the overall photovoltaic performance of the devices by about 11%. A non-monotonic change in the open circuit voltage (V oc ), short circuit current (I sc ) and fill factor (FF) was noticed due to temperature changes. A reasonable batch-to-batch reproducibility was achieved, accentuating a stable operation of the devices under thermal variations.

The optoelectronic parameters of tris (8-hydroxyquinoline) gallium (Gaq3) films were tuned by means of post-deposition thermal annealing under nitrogen gas. Nanostructure evolution was seen to play a vital role in the variation of the optoelectronics parameters of these films. The results showed an increased refractive index from 1.53 to ultra-high refractive index of 5.45, along with a maximized dielectric constant of 13.92 and optical conductivity of 56.31 S/cm when the films were annealed at 235 °C. At higher annealing temperature of 255 °C, a decreased trend was noticed for the aforementioned optoelectronic parameters and the grown amorphous nanorods were completely degraded, which has led to the formation of crystalline portions. The results were interpreted in terms of molecular packing density and structural variations. The investigated Gaq3 films were seen to obey Wemple–DiDomenico single oscillator model to provide information regarding the band gap and its strength. The achieved results are greatly important for the application of OLED displays technology and their performance improvement.

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 work the impact of sunlight intensity and ambient temperature on the inorganic solar panels in winter climate (22 November 2015) at Sarwchawa, Kurdistan Region, Iraq was carried out. A maximum intensity of sunlight (106.25 klux) was reached at 12:00 PM. However, beyond 12:00 PM the intensity showed a non-monotonic change behavior. This was ascribed to the change of sun position, its orientation and the direction at which the surface of the panel is illuminated. Results showed that the increase of sunlight intensity has made Isc to increase, while that of the Voc remains relatively unchanged. The reason why Isc is more affected by the sunlight intensity was understood from the fact that charge carriers acquire enough kinetic energy to move towards their corresponding electrodes before they relapse or recombine together, while as Voc is mostly correlated to the energy gap. There was a trivial decrement of efficiency with the increase of temperature. This was where the FF showeda reverse trend of increment with the increase of temperature. Noteworthy, at the points where the fill factor was decreased the efficiency was increased and vice versa.

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 a new solution processable small organic material, namely 2,2′-bithiophene end-capped dihexyloxy phenylene pentamer (BHBT2) was synthesized, characterized and applied in the fabrication of an organic ultraviolet photodetector. The material was synthesized via Williamson etherification, bromination and Suzuki coupling. FTIR and NMR spectroscopies were recorded for BHBT2 along with its optical, thermal and electrochemical properties. Finally, BHBT2 was used as donor material to produce a solution-processed UV photodetector based on a BHBT2 : PC61BM organic active layer. Results showed that in forward biasing, the photodetector exhibited a photovoltaic effect with Jsc = 1.80 mA, Voc = 0.66 V, FF = 0.30 and PCE = 0.98%, while in reverse biasing, the photodetector exhibited a fast, reversible and stable response with the highest detectivity of 1.47 × 109 jones. The realization of efficient UV detection was attributed to the strong absorption of BHBT2 and PC61BM in the UV region. Hence, the BHBT2 pentamer coupled with PC61BM can be considered as a potential material to be applied in a solution-processed organic UV photodetector.

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.

In this research work, numerical simulations are performed to correlate the photovoltaic parameters with various internal and external factors influencing the performance of solar cells. Single-diode modeling approach is utilized for this purpose and theoretical investigations are compared with the reported experimental evidences for organic and inorganic solar cells at various electrical and thermal conditions. Electrical parameters include parasitic resistances (Rs and Rp) and ideality factor (n), while thermal parameters can be defined by the cells temperature (T). A comprehensive analysis concerning broad spectral variations in the short circuit current (Isc), open circuit voltage (Voc), fill factor (FF) and efficiency (eta;) is presented and discussed. It was generally concluded that there exists a good agreement between the simulated results and experimental findings. Nevertheless, the controversial consequence of temperature impact on the performance of organic solar cells necessitates the development of a complementary model which is capable of well simulating the temperature impact on these devices performance. This work was financially supported in part by Research University Grant (RUG), UTM Malaysia (Vot:Q.J130000.21A2.03E00), and in part by the University of Human Development Scopus

In this study, solution processed composite films of nickel phthalocyanine (NiPc) and cobalt phthalocyanine (CoPc) are deposited by drop casting and under centrifugal force. The films are deposited on surface-type inter-digitated silver electrodes on ceramic alumina substrates. The effects of illumination on the impedance and capacitance of the NiPc CoPc composite samples are investigated. The samples deposited under centrifugal force show better conductivity than the samples deposited by drop casting technique. In terms of impedance and capacitance sensitivities the samples fabricated under centrifugal force are more sensitive than the drop casting samples. The values of impedance sensitivity (Sz) are equal to (-1.83) MWcm2/mW and (-5.365) MWcm2/mW for the samples fabricated using drop casting and under centrifugal force, respectively. Similarly, the values of capacitance sensitivity (Sc) are equal to 0.083 pFcm2/mW and 0.185 pFcm2/mW for the samples fabricated by drop casting and under centrifugal force. The films deposited using the different procedures could potentially be viable for different operational modes (i.e., conductive or capacitive) of the optical sensors. Both experimental and simulated results are discussed. Scopus

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

Cross-shaped resonators were proposed to improve the light absorption in the organic active layers, namely P3HT, PCBM and P3HT:PCBM hetero-structure. The resonator was made of aluminium (Al) which was encrusted on top of the organic active layers backed with indium tin oxide (ITO) coated glass. Simulated results showed that the proposed structure had significantly enhanced the light absorption in the organic thin films, whereby exhibited a broadband absorption in the visible and infrared spectra. An obvious redshift in the characteristic absorption peak of the organic thin films was observed, resulting in the reduction of their apparent energy gap due to the coupling effect between cross-shaped resonator and organic active layer as a consequence of light-matter interaction. It is concluded that the proposed metamaterial structure is beneficial to improve the performance of organic solar cells. Keywords: Metamaterial, Organic thin film, Light absorption, Cross resonator, Solar cell

The behavior of solar cells and modules under various operational conditions can be determined effectively when their intrinsic parameters are accurately estimated and used to simulate the current-voltage (I-V) characteristics. This work proposed a new computational approach based on approximation and correction technique (ACT) for simple and efficient extraction of solar cells and modules parameters from the single-diode model. In this technique, an approximated value of series resistance (Rs) was first derived and used to determine the initial value of parallel resistance (Rp). Later, the final corrected values of Rs and Rp were obtained by resubstituting their approximated values in a five-loop iteration using the manipulated equations. For rapid evaluation and validation of the proposed technique, a software application was also created using MATLAB program. The correctness and robustness of the proposed technique was validated on five types of solar cells and modules operated at varied temperatures and irradiances. The lowest RMSE value was achieved for RTC France (7.78937E-4) and PVM 752 GaAs (2.10497E-4) solar cell. The legitimacy of ACT extracted parameters was established using a simple yet competitive implementation approach wherein the performance of the developed technique was compared with several state-of-the-art methods recently reported in the literature.

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.