Conjugated donor-acceptor polymers have been regarded as attractive organic semiconductors for perovskite solar cells (PSCs) as hole-transport materials (HTMs). Herein, we report the design of four novel (X-DAD)n conjugated polymers based on alternating benzodithiophene unit (X) and thiophene-spaced benzene derivatives or pyridine (A). The variation of A building blocks has been shown to control the backbone geometry, which is crucial for achieving high charge-transport characteristics of HTMs. Particularly, introducing fluorine and methoxy-substituted blocks enabled rigid and planar backbone structure of PBPh-ff and PBPh-mm HTMs due to non-covalent intramolecular interactions. Benefiting from this merit, PBPh-ff and PBPh-mm exhibited improved hole mobilities and better hole extraction ability from MAPbI3. As a result, employing PBPh-ff as the HTM in n-i-p PSCs provided power conversion efficiency of 19.1% with an outstanding fill factor of ca. 80%. These findings highlight the importance of molecular design and geometry control of hole-transporting polymers for efficient perovskite photovoltaic devices. The control of backbone geometry is found to be important for reaching enhanced charge-transport characteristics of newly designed polymeric HTMs. Encouraging efficiency of 19.1% with good stability for p-i-n PSCs is achieved.

Organic semiconductor small molecules have gained significant attention as interfacial hole-transport materials (HTM) for application in perovskite solar cells (PSCs). Herein, we report the investigation of three donor-acceptor small molecules...

Organic solar cells have been intensively developed worldwide during the last two decades. After breaking the psychological barrier of 10% in power conversion efficiency (PCE), which was accomplished in 2011 by Mitsubishi Chemical, many academic and industry research groups generated tens of promising material combinations delivering PCEs>10%–11%. In spite of impressive efficiencies reached for small-area devices, it is still a big challenge to push this technology from labs to industry. The list of main obstacles includes low stability of vast majority of organic materials, limiting device lifetime; problematic upscaling related to the low reliability of large-area processing thin composite films with crystalline domains; and, finally, high cost of raw organic materials. To solve these challenges, principally new materials are urgently needed. In this chapter, we summarize the main principles of designing efficient electron donor conjugated polymers, discuss the relationships between the molecular structures and properties of the designed nanomaterials with their performance in real devices, and outline the material design strategies, which are expected to lead the further progress in the field.

A novel alternating TBTBT ("T" - thiophene, "B" - benzothiadiazole) compound has been synthesized from readily available precursors using efficient direct arylation and Stille cross-coupling reactions. Molecular structure of TBTBT has been revealed using single-crystal X-ray diffraction. TBTBT was applied as electron donor material for vacuum-processed small-molecule planar and bulk heterojunction solar cells and ambipolar semiconductor for organic field-effect transistors.

We report an unusual thermal condensation of readily available tetracyanocyclopropanes to tetracyanosubstituted triazaphenalenes, which revealed interesting optoelectronic properties such as strongly pronounced solvatochromism and bright photoluminescence. Optical memory elements and organic light emitting diodes with a deep red electroluminescence were designed using triazaphenalenes, thus highlighting the potential of these compounds as materials for electronic applications.

Three alternating (X–DADAD)n-type copolymers bearing different building blocks (X) in combination with benzoxadiazole (A) and thiophene (D) units were synthesized and studied as photoactive materials in organic solar cells. Superior short circuit currents and power conversion efficiencies (up to 4.4%) were reached when thiophene rather than fluorene or benzodithiophene was used as an X unit.

A carbazole-to-fluorene ratio in the molecular structure of the title polymers was found to have a strong effect on the morphology of their composites with the fullerene derivatives ([60]PCBM and [70]PCBM) and their photovoltaic performance.

We report the application of a statistical Suzuki-Miyaura polycondensation reaction for synthesis of a family of carbazole-fluorene-TTBTBTT terpolymers with tailored physical and optoelectronic properties. Organic bulk heterojunction solar cells based on the designed materials with optimal fluorene to carbazole ratios yielded reproducible power conversion efficiencies of 6.5-6.7%.