Teketel Yohannes Anshebo

• Prof. of Physical Chemistry
• Professor (Full) at Addis Ababa University

The noticeable growth in the power conversion efficiency of solution-processed organo-inorganic halide perovskite solar cells (OIHPSCs) incited the photovoltaic community to look for limitations that hurdle the commercialization process. The surface and interface defects between the perovskite and electron transport layers are among the main challe...

Recently, transition metal-based electrocatalysts have shown significant promise in promoting the oxygen evolution reaction (OER) as a result of their ample availability, tunable electronic properties, and catalytic capabilities. This study presents the synthesis of a transition metal-based electrocatalyst, featuring Co and Ni nanoparticles grown o...

The unprecedented increase in power conversion efficiency (PCE) of low‐cost organo‐inorganic halide perovskite solar cells (OIHPSCs) toward its Shockley‐Queisser limit intriguingly has prompted researchers to investigate the disadvantages of these devices. The issue of operational stability is the main hurdle challenging the way forward for commerc...

An understanding of the nature of molecular interactions among the ion pairs of 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide [EMI[FSI]] can offer a starting point and significant insight into the more dynamic and multiple interactions within the bulk liquid state. In this context, close inspection of ion pair conformers can offer insight in...

Density functional theory (DFT) calculations with Grimme’s B97D functional including dispersion are employed to provide both structural and electronic insight into the multifold interactions occurring in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquid [EMI][TFSI], which is currently being targeted for applications in next...

We used molecular dynamics (MD) simulations based on classical force field to provide the liquid structure in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquid in the presence of ethylene, dimethyl carbonate co-solvents and 1M LiTFSI mixtures which are currently being targeted for applications in next-generation Li-ion batt...

The development of ambient-air-processable organic–inorganic halide perovskite solar cells (OIHPSCs) is a challenge necessary for the transfer of laboratory-scale technology to large-scale and low-cost manufacturing of such devices. Different approaches like additives, antisolvents, composition engineering, and different deposition techniques have...

Among all possible ionic liquids, which are potential candidates for electrolytic solvents in lithium ion batteries, 1-ethyl-3-methylimidazolium bis(fuorosulfonyl)imide [EMI[FSI] is the most noteworthy, mainly due to its lower viscosity. To further advance the development of electrolytes with improved electrochemical performance, it is imperative t...

Ionic liquids (IL) can be modified into hybrid electrolytes, either with lithium salts and/or organic solvents, which can effectively reduce the viscosity and ionic transferring resistance, which thereby improves the ion transport and interfacial properties of battery electrolytes. Several IL based electrolytes with an imidazolium cation (EMI) have...

Both density functional theory (DFT) and molecular dynamics (MD) based on classical force field were used to provide both structural and electronic insight into the multifold interactions occurring in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquid in the presence of ethylene carbonate and dimethyl carbonate co-solvent mi...

The deterioration of the quality of groundwater by fluoride is the cause of shortage of drinking water supply in the rift valley region. Most people living in the rural areas are using groundwater as the source of their potable water; however, it is contaminated with high concentrations of fluoride ion above the permissible level. Hence, this study...

Outstanding improvement in power conversion efficiency (PCE) over 25% in a very short period and promising research developments to reach the theoretical PCE limit of single junction solar cells, 33%, enables organic–inorganic perovskite solar cells (OIPSCs) to gain much attention in the scientific and industrial community. The simplicity of produc...

In most African rural communities, ground water is the primary source of drinking water. Fluoride is a harmful substance found in ground water that causes serious health problems. The only answer to the fresh and clean water crisis is water treatment. Sustainable, cost-effective and efficient membrane filtration technologies are becoming progressiv...

Today, the issue of the environment is the concern of scientists worldwide. Aside from developed countries, developing countries are revolutionizing their economy from agriculture to industries, aggravating the discharge of pollutants. Textile industries are the main sources of pollutant dyes such as methylene blue (MB). In this study, a simple and...

The large-scale production of high-quality graphene is the major focus of scientists and engineers recently. However, its massive manufacturing routes from its precursor graphene oxide (GO) are involved in the production of toxic gasses and consist of hazardous explosive steps that severely hurt and threaten ecological balance and human health. The...

In this work, the effect of DIM on the PCE and photostability of PCDTBT:PC 71 BM PSCs was investigated. DIM is an effective additive in a BHJ PCDTBT:PC 71 BM solar cell since it fulfills the requirement of a selective PC 71 BM dissolution. PCE of the device based on PCDTBT:PC 71 BM processed with DIM is higher than that of the reference device. In...

Nanocomposites of Zn-Ti-Fe oxide using zinc as a host with different ratios of precursor salts were prepared by co-precipitation method to use as semiconductors for dye sensitized solar cell (DSSC). The as-synthesized nanocomposites were characterized using XRD, SEM-EDX, TEM and UV-Vis spectrophotometer. DSSCs based on the new semiconductors and di...

Effect of Structure on Charge transport: In connection with Substituted Side Chains on polymer backbones

In this investigation, photovoltaic (PV) parameters improvements in poly[2,6-(4,4 '-bis( 2-ethylhexyl) dithieno[3,2-b:2',3'-d]silole)-alt-5,5'-(3,6-bis[4-(2-ethylhexyl) thienyl-2-yl]-s-tetrazine] and fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester (PDTSTTz: PCBM) blend were made through solvent additives and secondary donor addition...

We present two co-polymer families; one based on a thiophene-quinoxaline unit and one on a thiophene-pyrido pyrazine unit. Co-polymerization of these monomers with thiophene-hexylthiophene was performed to create polymers with an optical absorption that fully covers the visible part of the solar spectrum with the aim to enhance the solar cell perfo...

Accurate characterization and reporting of organic photovoltaic (OPV) device performance remains one of the important challenges in the field. The large spread among the efficiencies of devices with the same structure reported by different groups is significantly caused by different procedures and equipment used during testing.The presented article...

This study employs anthocyanin extracts from mulberry (Morus atba Lam) fruit and Akenchira (Striga hermonthica) flower as the natural dyes for a dye-sensitized solar cell (DSSC). The electrodes, electrolyte (I-/I-3(-)), and dyes were assembled into a cell and illuminated by a light with an intensity 100 mW/cm(2) to measure the photoelectrochemical...

Poly(phenylene ethynylene)‐alt‐poly(phenylene vinylene)s (PPE‐PPVs) with various thiophene units (thiophene, bithiophene, and 3,4‐ethylenedioxythiophene) at the X position, with the general backbone design (PhCCXCCPhCHCHPhCHCH), bearing identical solubilizing side chains at the phenylene rings of the polymers, are synthesized to study the effect of...

The variation of the drift mobility of positive and negative charge carriers in fi lms of anthracene- containing poly( p -phenylene-ethynylene)- alt- poly( p -phenylene-vinylene)s ( AnE-PVs ), differently substituted, is investigated as a function of the applied electric fi eld. Branched 2-ethylhexyl and linear alkoxy side chains of different lengt...

Dye-sensitized solar cells (DSSCs) were fabricated using natural dyes extracted from flowers of Amaranthus caudatus, Bougainvillea spectabilis, Delonix regia, Nerium oleander, Spathodea companulata and a mixture of the extracts. The photoelectrochemical cell (PEC) performance of the DSSCs of these dyes showed fill factors (FF) mostly higher than 50...

Nanocomposites of Sn-Ti oxide were prepared by sol-gel method to use as photo anode for dye sensitized solar cell (DSSC). Crystal size, elemental contents, structural properties and energy band gaps of the as-synthesized powders was examined using XRD, EDX, SEM and UV-Vis spectrophotometer respectively. A quasi-solid state photo electrochemical sol...

The effects of a moderate variation of the molecular weight on the optical, structural, morphological and transport properties of an anthracene-containing PPE-PPV copolymer are investigated, as well as their overall implication on the photovoltaic parameters of bulk-heterojunction solar cells. Just a two-fold variation in the molecular weight is en...

A solid-state photoelectrochemical solar energy conversion device based on blend of poly(3-hexylthiophene) (P3HT) and 1-(3-methoxycarbonyl)propyl-1-phenyl[6,6]C61 (PCBM), and an amorphous poly(ethylene oxide) complexed with I3-/I- redox couple has been constructed and characterized. The photoelectrochemical performance parameters of the device were...

A study on dye-sensitized solar cells (DSSCs) with extracts of Syzygium guineense as sensitizer is reported for the first time. DSSCs were assembled using natural dye extracted from Syzygium guineense as sensitizer. The photoelectrochemical performance of the quasi-solid state DSSCs based on the ethanol extract dye showed VOC of 0.506 V and JSC of...

A solid state photoelectrochemical solar energy conversion device based on nanocrystalline-TiO 2 sensitized with Di-Tetrabutylammoniumcis-bis(isothiocyanato)bis(2,2'-bipyridyl-4,4'-dicarboxylato)-ruthenium(II) (N719) dye has been constructed and characterized. The current density–voltage characteristics in the dark and under white light illuminatio...

Poly{[2,7-(9,9-bis-(2-ethylhexyl)-fluorene)]-alt-[5,5-(4,7-di-2′-thienyl-2,1,3-benzothiadiazole)]}: PCBM bulk heterojunction solar cells were fabricated and characterized under different incident light power intensities. Charge-trapping effects take place at low fullerene content in the photoactive blend; an efficient polymer fullerene intermixing...

The synthesis and characterization of a novel polythiophene substituted with a 2′-pentyloxy-5′-(1″′-oxooctyl) phenyl group (PPOPT) is reported. The bulk transport properties of thin films of PPOPT are investigated by admittance spectroscopy. The dramatic effect of the phenyl side chain on the mobility of positive carriers in films of PPOPT is descr...

Transport of holes in thin films of a low-bandgap alternating polyfluorene copolymer, APFO-Green5, was investigated by means of admittance spectroscopy as a function of field and temperature. The values of hole mobility were evaluated from the position of the maxima in the plots of the negative differential susceptance as a function of frequency. H...

A 1:1 mixture of two thiophene based poly(p-phenylene ethynylene)-alt-poly(p-phenylene vinylene)s denoted DO-PThE1-PPV2 (D1) and MEH-PThE1-PPV2 (D2), consisting of the same conjugated backbone but different types and volume fraction of alkoxy side chains on the phenylene ethynylene unit, has led to enhanced charge carrier mobility (measured using C...

Difference infrared spectra between illumination and dark of a polyethylenedioxythiophene (PEDOT) covered germanium electrode in contact with the electrolyte solution and under applied potential are shown. The spectra show a different behavior at different redox (doping) states of the polymer. The photoinduced formation of positive charge carriers...

The bulk transport properties of positive carriers in thin films of a low band-gap conjugated polymer, called APFO-Green5, have been investigated in the ac regime. The frequency-dependent impedance of an ITO/PEDOT:PSS/APFO-Green5/Al structure (where ITO is indium tin oxide and PEDOT:PSS is poly(3,4-ethylenedioxythiophene)/polystyrene sulphonic acid...

Transport of holes in a low band gap polyfluorene, APFO-Green6, was investigated by means of admittance spectroscopy in the modulation frequency range 1–10⁶ Hz . At room temperature, hole mobility of APFO-Green6 is dependent on the applied electric field, as commonly observed in disordered organic materials. The excess capacitance toward...

In situ attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroelectrochemistry during oxidation (p-doping) and reduction (n-doping) of three phenyl-substituted polythiophenes, namely POPT, PEOPT and POMeOPT is presented. All the three phenyl substituted polythiophenes show both n- and p-doping. The infrared active vibration (IRAV...

Poly[3-(2′,5′-dioctyloxyphenyl)thiophene] (PDOOPT), poly[3-(2′,5′-diheptyloxyphenyl)thiophene] (PDHOPT) and poly[3-(2′,5′-dibutyloxyphenyl)-thiophene] (PDBOPT) have been prepared electrochemically from their monomers within nanocrystalline titanium dioxide (nc-TiO2) porous surface deposited on indium doped tin oxide coated glass (ITO-glass) for sol...

Poly[3-(2',5'-diheptyloxyphenyl)thiophene], PDHOPT, has been prepared electrochemically from its monomer for solar cell application. PDHOPT exhibits a band gap of 2.1 eV. The redox properties of PDHOPT were characterized using cyclic voltammetry. The estimated energy levels of the highest occupied molecular orbital (HOMO) and the lowest u...

A solid-state photoelectrochemical cell based on polymer-sensitized nanocrystalline titanium dioxide (nc-TiO2) was constructed and studied for its photoresponse behavior. Poly[2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and Poly[oxymethylene-oligo(oxyethylene)] (POMOE), complexed with I3-/I- redox couple were used as a poly...

A comparative study was done between liquid-state photoelectrochemical cells (PECs) consisting of photoactive electrodes of poly(3-hexylthiophene), P3HT, and a composite film of nanocrystalline titanium dioxide (nc-TiO2) and P3HT. The nc-TiO2/P3HT based device shows better performance with an open-circuit voltage of 0.51V, a short-circuit current o...

Photoelectrochemical cells (PECs) have been fabricated using the emeraldine base form of polyaniline (EB) as a photoactive material and Eu2+/Eu3+ redox couple in methanol as an electrolyte. A PEC with a structure: Glass/ITO/EB/electrolyte/Pt produces an open-circuit voltage (VOC) of –0.132 V and a short-circuit current (ISC) of 0.64 µA cm-2 under 5...

The copolymer, poly(3-methylthiophene-co-3-octylthiophene), was electrochemically synthesized from a mixture of 3-methylthiophene and 3-octylthiophene. Once the best condition for the copolymer formation was obtained a solid-state photoelectrochemical cell (PEC) was constructed and studied. The PEC contains the photoactive material poly(3-methylthi...

A solid-state photoelectrochemical solar energy conversion device based on blend of poly(3-hexylthiophene) (P3HT) and fullerene (C60) has been constructed and characterized. The photoelectrochemical performance parameters of the device were compared with pure P3HT solid-state photoelectrochemical cell. The current–voltage characteristics in the dar...

New solution-processable, anthrancene- and benzothiadiazole-containing polyfluorene copolymers (P1-P3) have been synthesized and characterized. The preparation and characterization of the corresponding blue light-emitting devices are also reported. Polymers P2 and P3 show high photoluminescence efficiency while polymer P2 does not show any signific...

The solvatochromic and thermochromic behaviours of phenyl-substituted polythiophenes were studied. The pristine polymers, upon dissolution in chloroform, exhibited blue-shifted absorption. The solid films of the polymers showed significant blue-shifted as well as red-shifted absorptions when heated. While the addition of methanol to the chloroform...

In situ attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroelectrochemistry during oxidation (p-doping) and reduction (n-doping) as well as photoinduced infrared spectroscopy of a random copolymer of 2,3,5,6-tetrafluoro-1,4-phenylenevinylene and 2,5-dioctyloxy-1,4-phenylenevinylene [co(TFPV-DOPV)] is presented. The infrared ac...

The photoelectrochemical properties of a solid-state photoelectrochemical cell (PEC) based on poly(3-hexylthiophene), P3HT, and an ion-conducting polymer electrolyte, amorphous poly(ethylene oxide), POMOE, complexed with I3−/I− redox couple has been constructed and studied. The current–voltage characteristics in the dark and under white light illum...

Bulk heterojunction solar cells based on blends of photoactive layers of polyfluorene copolymer Poly((2,7-(9-(2′-ethylhexyl)-9-hexyl-fluorene)-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole))-co-(2,7-(9-(2′-ethylhexyl)-9-hexyl-fluorene)-alt-2,5-thiophene)) (LBPF3) acting as electron donor, and [6,6]-phenyl-C61-butyric acid methylester (PCBM)...

Information on doping- and photoinduced phenomena and processes in materials used in organic polymeric photovoltaic systems (plastic solar cells) can be obtained using infrared spectroscopy. The methods and results for the identification of doping- and photoinduced charge carriers, investigation of charge carriers in electrochemical systems, and st...

The photoinduced formation of charge carriers in polyethylenedioxythiophene (PEDOT) on a Ge electrode in contact with the electrolyte solution under applied potential are studied by in situ IR spectroscopy. Difference spectra between illumination and dark show the formation of positive charge carriers in the neutral (undoped) form, wheras no signif...

In situ UV-VIS-NIR and Raman spectroelectrochemical studies of polybenzimidazobenzophenanthroline (BBL), a conjugated ladder polymer, are reported. BBL films were reduced potentiostatically in spectroelectrochemical cells suitable for in situ UV-VIS-NIR and in situ Raman spectroscopy. The polymer shows four reversible reduction processes during n-d...

A comparison of doping and photoinduced IRAV spectra of conjugated polymers with more complex structures is presented. Differences in behavior regarding the comparison of p- and n-doped states of different materials were observed. In contrast, a comparison between doped and photoinduced IRAV spectra often show a similar band pattern. Our results do...

Polybenzimidazobenzophenanthroline (BBL), a conjugated ladder polymer, has interesting features such as n-type conductivity, good photoconductivity, large nonlinear optical properties and the highest electron affinity among known n-type semiconducting polymers, which makes the material an interesting candidate for optoelectronical applications. BBL...

Spectroelectrochemical techniques have been used to study doping-induced reactions in conjugated polymers. Here, we report results on reduction reactions (n-doping) of the conjugated ladder polymer polybenzimid-azobenzophenanthroline (BBL). The spectra are recorded in situ during applied potential in a three-electrode spectroelectrochemical cell. T...

Fourier transform infrared (FTIR) spectroscopy is a powerful method to determine the doping induced structural changes and electronic band structure modifications of conjugated polymer films. Here, we report in situ attenuated total reflection (ATR) FTIR spectroelectrochemical results of reduction reactions (n-doping) of the conjugated ladder polym...

The behaviour of an all-solid-state photoelectrochemical cell containing a conjugated polymer, poly[3-(4-octylphenyl)-2,2′-bithiophene], film as a photoactive electrode, a solid polymer electrolyte, poly[oxymethylene-oligo(oxyethylene)] complexed with redox couple, and a counter electrode was studied. The cell converted light to electricity, operat...

We show how the present generation of polymer electrolytes may be used in conjunction with conjugated and electroactive polymers to enable polymeric electrochromic and photoelectrochemical devices. The processing properties of both classes of polymers enables the formation of thin layer devices, and the molecular engineering of the conjugated polym...

The photoelectrochemical properties of all-solid-state photoelectrochemical cell constructed from a conjugated polymer poly[3-(4-octylphenyl)thiophene] and an amorphous poly(ethylene oxide) complexed with iodide/triiodide redox couple were studied. In order to develop flexible photoelectrochemical cells, we have used a transparent polymeric metal,...

Highly efficient photovoltaic devices, constructed using polythiophene derivatives blended with fullerenes, are described. The photovoltaic behavior of the sandwich-structure devices (current-voltage characteristic, conversion efficiency) is reported and the electrical, optical (optical absorption, photoluminescence), and morphological properties o...

The copolymers poly(3-methylthiophene-co-3,4-ethylenedioxythiophene) were prepared from mixtures of 3-methylthiophene and 3,4-ethylenedioxythiophene via electrochemical oxidation. Various concentrations of the monomers in the mixture at a fixed polymerization potential, or fixed concentrations of the monomers in the mixture at various polymerizatio...

A photoelectrochemical cell based on neutral poly(3-methylthiophene) electrochemically coated on indium—tin oxide as a photoactive electrode, an amorphous poly(ethylene oxide) complexed with an I3−/I− redox couple as a solid polymer electrolyte, and thin transparent platinum film vapour deposited on indium—tin oxide as a counter electrode has been...

All‐solid‐state photoelectrochemical cells have been constructed using films of a conducting polymer, poly(3‐octylthiophene), and a polymer electrolyte, amorphous polyethylene oxide, complexed with the redox couple. An open‐circuit voltage of 250 mV and a short‐circuit current of 0.04 μA/cm2 were obtained with white light illumination at approxim...