Metal chalcogenides such as copper zinc tin sulfide (CZTS) have been intensively studied as potential photovoltaic cell materials, but their viability have been marred by crystal defects and low open circuit potential (Voc) deficit, which affected their energy conversion efficiency. Strategies to improve on the properties of this material such as alloying with other elements have been explored and have yielded promising results. Here, we report the synthesis of CZTS and the partial substitution of S with Te via anion hot injection synthesis method to form a solid solution of a novel kesterite nanomaterial, namely, copper zinc tin sulfide telluride (CZTSTe). Particle-size analyzed via small angle X-ray scattering spectroscopy (SAXS) confirmed that CZTS and CZTSTe materials are nanostructured. Crystal planes values of 112, 200, 220 and 312 corresponding to the kesterite phase with tetragonal modification were revealed by the X-ray diffraction (XRD) spectroscopic analysis of CZTS and CZTSTe. The Raman spectroscopy confirmed the shifts at 281 cm−1 and 347 cm−1 for CZTS, and 124 cm−1, 149 cm−1 and 318 cm−1 for CZTSTe. High degradation rate and the production of hot electrons are very detrimental to the lifespan of photovoltaic cell (PVC) devices, and thus it is important to have PVC absorber layer materials that are thermally stable. Thermogravimetric analysis (TGA) analysis indicated a 10% improvement in the thermal stability of CZTSTe compared to CZTS at 650 °C. With improved electrical conductivity, low charge transfer resistance (Rct) and absorption in the visible region with a low bandgap energy (Eg) of 1.54 eV, the novel CZTSTe nanomaterials displayed favorable properties for photovoltaics application.
The hexathienylbenzene-co-poly(3-hexylthiophene-2,5diyl) (HTB-co-P3HT) conducting polymer was synthesized by oxidative co-polymerization of hexathienylbenzene (HTB) and 3-hexylthiophene using iron chloride (FeCl3) as an oxidant. The effect of chlorobenzene, toluene and chloroform on the optoelectronic characteristics of the polymer was investigated. The study revealed that spectroscopic and electrochemical responses of HTB-co-P3HT are affected by the nature of the solvent. The lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) energy levels of HTB-co-P3HT were determined from cyclic voltammetry (CV) and were compared to those of (6,6)-Phenyl C71 butyric acid methyl ester (PC71BM) and it was found that the LUMO energy levels of HTB-co-P3HT in toluene were lower than those for chlorobenzene and chloroform. The electrochemical impedance spectroscopy (EIS) analysis also revealed the thin film of HTB-co-P3HT prepared using toluene as the most conductive. However, the photovoltaic parameters of the HTB-co-P3HT organic photovoltaic cells (OPVs) departed from the favored toluene and noted chlorobenzene as being the advantageous solvent. We obtained a power conversion efficiency (PCE) of 0.48%, fill factor (FF) of 27.84%, current density (JSC) of 4.93 mA.cm−2 and open circuit voltage (VOC) of 0.35 V in chlorobenzene, a PCE of 0.30%, FF of 26.08%, JSC of 5.00 mA.cm−2 and VOC of 0.23 V in chloroform and finally, a PCE of 0.33%, FF of 25.45%, JSC of 5.70 mA.cm−2 and VOC of 0.23 V in toluene.
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