Isomeric carbazolocarbazoles: synthesis, characterization and comparative study in Organic Field Effect Transistors

We report here the synthesis and characterization of a new family of isomeric carbazolocarbazole derivatives, namely carbazolo[1,2-a]carbazole, carbazolo[3,2-b]carbazoleand carbazolo[4,3-c]carbazole. Thermal, optical, electrochemical, morphological and semiconducting properties have been studied to understand the influence of geometrical isomerism on the optoelectronic properties of these compounds. Different packing patterns have been observed by single crystal X-ray diffraction (XRD) which then correlate with the different morphologies of the evaporated thin films studied by XRD and Atomic Force Microscopy (AFM). The effect of N-substituents has also been evaluated for one of the isomers revealing a noticeable influence on the performance as organic semiconductors in Organic Field Effect Transistors (OFETs). A good p-channel field effect has been determined for N,N′-dioctylcarbazolo[4,3-c]carbazole with a mobility of 0.02 cm2 V−1 s−1 and Ion/Ioff ratio of 106 in air. These preliminary results demonstrate the promising properties of molecular carbazolocarbazole systems which should be further explored in the area of organic semiconducting materials

Hole transporting layers in printable solar cells

The incessant evolution of organic and hybrid solar cells has demonstrated that a multilayer architecture is required for an optimum device functioning. Although more attention has been traditionally focused on the active layer materials, it is the interfacial materials, placed between the electrodes and the active region, which might play some of the most critical roles in the solar cell. In this regard, interfacial layers can modulate the compatibility between the electrodes and the active layers in terms of morphology, surface energy or energy level alignment. Furthermore, interfacial layers modulate the light absorption working as optical spacers, assist in the exciton confinement and preserve the active layer from damage or degrada tion. However, the most important role of interfacial layers concerns the charge transport, defining an energy gradient for the selective migration of free charge carriers from the active layer to the electrodes. This chapter offers a comprehensive description of those materials specifically working as hole transporting layers in organic, dye-sensitized and perovskite solar cells. Conjugated polymers, small molecules, metals, metal oxides, self-assembled monolayers, carbon nanotubes and graphene-based materials will be discussed along with their influence on different aspects aimed at the optimization of the solar cell performance

2D-Self-Assembled Organic Materials in Undoped Hole Transport Bilayers for Efficient Inverted Perovskite Solar Cells

Interfaces between photoactive perovskite layer and selective contacts play a key role in the performance of perovskite solar cells (PSCs). The properties of the interface can be modified by the introduction of molecular interlayers between the halide perovskite and the transporting layers. Herein, two novel structurally related molecules, 1,3,5-tris(α-carbolin-6-yl)benzene (TACB) and the hexamethylated derivative of truxenotris(7-azaindole) (TTAI), are reported. Both molecules have the ability to self-assemble through reciprocal hydrogen bond interactions, but they have different degrees of conformational freedom. The benefits of combining these tripodal 2D-self-assembled small molecular materials with well-known hole transporting layers (HTLs), such as PEDOT:PSS and PTAA, in PSCs with inverted configuration are described. The use of these molecules, particularly the more rigid TTAI, enhanced the charge extraction efficiency and reduced the charge recombination. Consequently, an improved photovoltaic performance was achieved in comparison to the devices fabricated with the standard HTLs.The authors are grateful for the financial support from the Ministry of Science, Innovation and Universities (Projects RTI2018-101092–B-I00, PID2021-122734OB-I00), Fundación Séneca–Agencia de Ciencia y Tecnología de la Región de Murcia (Projects 20959/PI/18, 22058/PI/22), Programa Estatal de Fomento de la Investigación Científica y Técnica de Excelencia (RED2018-102815-T), and University Jaume I (Project EPCESBI UJI-B2022-08)