Thieno[3,2-b]thiophene (TT) and dithieno[3,2-b;3,2-d]thiophene (DTT) have drawn immense attention in the field of electronics and optoelectronics. In this work, the first examples of TTs (TPE2-TT and TPE3-TT) and a DTT (TPE2-DTT), having tetraphenylethylene (TPE) at the periphery exhibiting aggregation induced emission (AIE) in OLEDs, were designed and synthesized by the Suzuki coupling reaction. Their properties were investigated through experimental and computational studies, as well as X-ray diffraction and DFT optimization. TPE2-TT showed excellent device performance with a maximum luminance of 11 620 cd m⁻², a maximum current efficiency of 6.17 cd A⁻¹ and a maximum external quantum efficiency of 2.43%. Moreover, these synthetically easily accessible molecules have high thermal stability, which makes them perfectly suitable for optical applications.

Two novel D–A (donor–acceptor) and one D–A–D small molecules containing mesitylborane as an acceptor and triphenylamine as a donor, linked through a thieno[3,2-b]thiophene π-conjugated spacer, are synthesized and characterized. Their photo- and electrochemical properties were investigated by experimental and computational studies. The emission quantum efficiencies were determined to be between 46% and 68% in THF. Their solid-state quantum yields were recorded up to 42%. The fabricated electroluminescent devices as emitting materials showed sky-blue to yellowish green emissions. Their devices exhibit high performance with a turn-on voltage, maximal brightness, and highest luminescence efficiency of up to 4.0 V, 1200 cd m⁻² and 1.13 cd A⁻¹, respectively. These results pave new avenues for the future molecules possessing D and A units connected via fused thiophenes.

Multi-walled carbon nanotube (MWCNT)/TiO₂ mesoporous networks can be employed as a new alternative photoanode in dye-sensitized solar cells (DSSCs). By using the MWCNT/TiO₂ mesoporous as photoanodes in DSSC, we demonstrate that the MWCNT/TiO₂ mesoporous photoanode is promising alternative to standard FTO/TiO₂ mesoporous based DSSC due to larger specific surface area and high electrochemical activity. We also show that iron pyrite (FeS₂) thin films can be used as an efficient counter electrode (CE), an alternative to the conventional high cost Pt based CE. We are able to synthesis FeS₂ nanostructures utilizing a very cheap and easy hydrothermal growth route. MWCNT/TiO₂ mesoporous based DSSCs with FeS₂ CE achieved a high solar conversion efficiency of 7.27% under 100 mW cm⁻² (AM 1.5G 1-Sun) simulated solar irradiance which is considerably (slightly) higher than that of A-CNT/TiO₂ mesoporous based DSSCs with Pt CE. Outstanding performance of the FeS₂ CE makes it a very promising choice among the various CE materials used in the conventional DSSC and it is expected to be used more often to achieve higher photon-to-electron conversion efficiencies.

With the purpose of obtaining white emission from single layer organic light emitting diodes (OLEDs), fluorene benzotriazole based polymers with double bond subunits (namely TP2 and SP3 with and without thiophene linker, respectively) were synthesized by a Suzuki cross-coupling polymerization reaction. SP3 and TP2 were used as an emissive layer of the OLED devices due to their outstanding solubility in organic solvents, photoluminescence intensity and morphological suitability for fine thin film-forming capability. The optical, electrochemical, light emission and electroluminescence characteristics, Density Functional Theory (DFT) calculations and admittance spectroscopic analysis of OLEDs based on SP3 and TP2 were realized in detail to understand the effects of thiophene linker addition as a donor unit to the main chain of fluorene benzotriazole based polymers. As a result, TP2 emitted a bright yellow emission with a maximum brightness of 243 cd m⁻² at 40 mA cm⁻², and a maximum current efficiency of 1.38 cd A⁻¹ with more broad electroluminescence characteristics than SP3 polymer without the thiophene linker. SP3 emitted a greenish yellow emission with a maximum brightness of 1001 cd m⁻² at 845 mA cm⁻², and a maximum current efficiency of 0.33 cd A⁻¹. Carrier transport properties, charge carrier transit time and the equivalent circuit modelling studies were obtained through admittance spectroscopy. An equivalent circuit model with a combination of two resistors and one capacitor explained the charge conduction mechanism of SP3 and TP2 based OLEDs. SP3 and TP2 OLED devices represented typical p-type transporting characteristics with mobilities of 0.073 and 0.017 cm² V⁻¹ s⁻¹, respectively with simplified device configuration. All the results indicate that thiophene addition to the main chain of fluorene benzotriazole based polymers with double bond subunits lead to a promising candidate for white emissive materials used in single layer white OLEDs.