Browsing by Author "Özdemir, Resul"

Now showing 1 - 4 of 4

A dopant-free 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT)-based hole transporting layer for highly stable perovskite solar cells with efficiency over 22%
(ROYAL SOC CHEMISTRY, 2022) Kaya, Ismail Cihan; Ozdemir, Resul; Usta, Hakan; Sonmezoglu, Savas; 0000-0002-7957-110X; 0000-0002-0618-1979; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Özdemir, Resul; Usta, Hakan
In this study, for the first time, n-i-p PSCs were fabricated using dopant-free 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) as the solution-processed hole transporting layer (HTL). The power conversion efficiency (PCE) of the optimized device with the C8-BTBT film that favored edge-on molecular alignment was 22.45% with negligible hysteresis. A thinner dopant-free C8-BTBT HTL effectively protected the perovskite layer from moisture resulting in better shelf-life stability for un-encapsulated PSCs, which maintained >80% of its initial PCE (after a period of 120 days) at a relative humidity level of 40-45%. In addition, the C8-BTBT-based PSCs kept their high performance with no obvious PCE loss at 60 degrees C for 20 days in the ambient atmosphere and retained 82% of their initial PCE at 85 degrees C for 10 days. Overall, our findings revealed that a thin solution-processed C8-BTBT HTL plays a critical role not only in hole extraction and transport but also in greatly improving the ambient and thermal stability of n-i-p PSCs.
FUNCTIONALIZED LOW LUMO [1]BENZOTHIENO[3,2-B][1]BENZOTHIOPHENE (BTBT)-BASED MOLECULAR SEMICONDUCTORS FOR ORGANIC FIELD EFFECT TRANSISTORS
(Abdullah Gül Üniversitesi, Fen Bilimleri Enstitüsü, 2021) Özdemir, Resul; AGÜ, Fen Bilimleri Enstitüsü, Malzeme Bilimi ve Makine Mühendisliği Ana Bilim Dalı
DAcTTs have provided an excellent π-framework for the development of high mobility p-type molecular semiconductors in the past decade. However, n-type DAcTTs are rare and their electron transporting characteristics remain largely unexplored. In the second chapter of this thesis, the first example of an n-type BTBT-based semiconductor, D(PhFCO)-BTBT, has been realized via a two-step transition metal-free process without using chromatographic purification. The corresponding TC/BG-OFET devices demonstrated μe (max) = ~0.6 cm2/Vs and Ion/Ioff ratio = 107-108. The large band-gap BTBT π-core is a promising candidate for high mobility n-type organic semiconductors and, combination of very large intrinsic charge transport capabilities and optical transparency, may open a new perspective for next-generation (opto)electronics. In the third chapter of this thesis, a series of BTBT-based small molecules, D(C7CO)-BTBT, C7CO-BTBT-CC(CN)2C7, and D(C7CC(CN)2)-BTBT, have been developed in “S-F-BTBT-F-S (F/S: functional group/substituent)” molecular architecture. Combining with D(PhFCO)-BTBT, a molecular library with systematically varied chemical structures has been studied herein for the first time for low LUMO DAcTTs, and key relationships have been elucidated. The molecular engineering perspectives presented in this thesis may give unique insights into the design of novel electron transporting thienoacenes for unconventional optoelectronics.
Interplay between Charge Injection, Electron Transport, and Quantum Efficiency in Ambipolar Trilayer Organic Light-Emitting Transistors
(WILEY, 2022) Moschetto, Salvatore; Benvenuti, Emilia; Usta, Hakan; Özdemir, Resul; Facchetti, Antonio; Muccini, Michele; Prosa, Mario; Toffanin, Stefano; 0000-0003-4099-8664; 0000-0001-5533-1585; 0000-0002-7957-110X; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Usta, Hakan
The fascinating characteristic of organic light-emitting transistors (OLETs) of being electrical switches with an intrinsic light-emitting capability makes them attractive candidates for a wide variety of applications, ranging from sensors to displays. To date, the OLET ambipolar trilayer heterostructure is the most developed architecture for maximizing device performance. However, a major challenge of trilayer OLETs remains the inverse correlation between external quantum efficiency and brightness under ambipolar conditions. The complex interconnection between electroluminescent and ambipolar charge transport properties, in conjunction with the limited availability of electron transport semiconducting materials, has indeed hampered the disruptive evolution of the OLET technology. Here, an in-depth study of the interplay of the key fundamental features that determine the device performance is reported by exploring electron transport semiconductors with different properties in ambipolar trilayer OLETs. Through the selection of compounds with tailored chemical structures, the relation between intrinsic optoelectronic characteristics of the electron transport semiconductor, energy level alignment within the structure, and morphological features is unraveled. Furthermore, the introduction of a suitable electron injector at the emissive/semiconducting layers interface sheds light into the bidimensional nature of OLETs that is a distinguishing factor of this class of devices with respect to prototypical organic light-emitting diodes.
Triisopropylsilylethynyl-substituted indenofluorenes: carbonyl versus dicyanovinylene functionalization in one-dimensional molecular crystals and solution-processed n-channel OFETs
(Royal Society of Chemistry, 2018) Özdemir, Resul; Park, Sangyun; Deneme, İbrahim; Park, Yonghan; Zorlu, Yunus; Ardic Alidağı, Hüsniye; Harmandar, Kevser; Kim, Choongik; Usta, Hakan; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü;
The design and synthesis of novel electron-deficient and solution-processable polycyclic aromatic hydrocarbons offers great opportunities for the development of low-cost and large-area (opto)electronics. Although (trialkylsilyl)ethynyl (R3Si–C C–) has emerged as a very popular unit to solubilize organic semiconductors, it has been applied only to a limited class of materials that are mostly substituted on short molecular axes. Herein, two novel solution-processable indenofluorenebased semiconductors, TIPS-IFDK and TIPS-IFDM, bearing (triisopropylsilyl)ethynyl end units at 2,8-positions (long molecular axis substitution) were synthesized, and their single-crystal structures, optoelectronic properties, solution-sheared thin-film morphologies/microstructures, and n-channel field-effect responses were studied. In accordance with the DFT calculations, the HOMO/LUMO energies of the new compounds are found to be -5.77/-3.65 eV and -5.84/-4.18 eV for TIPS-IFDK and TIPS-IFDM, respectively, reflecting the high electron deficiency of the new ?-backbones. Both semiconductors exhibit slightly S-shaped molecular frameworks with highly coplanar IFDK/IFDM ?-cores, and they form slipped ?-stacked one-dimensional (1-D) columnar motifs in the solid state. However, substantial differences in the degree of ?–? interactions and stacking distances (4.04 Å vs. 3.47 Å) were observed between TIPS-IFDK and TIPS-IFDM as a result of carbonyl vs. dicyanovinylene functionalization, which results in a three orders of magnitude variation in the charge carrier mobility of the corresponding thin films. Top-contact/bottom-gate OFETs fabricated via solution-shearing TIPS-IFDM yielded one of the best performances in the (trialkylsilyl)ethynyl literature (µe = 0.02 cm2 V-1 s -1 , Ion/Ioff = 107–108 , and VT ~ 2 V under ambient atmosphere) for a 1-D polycrystalline semiconductor microstructure. To the best of our knowledge, the molecules presented here are the first examples of n-type semiconductors substituted with (trialkylsilyl)ethynyl groups on their long molecular axes.