Herein, we report the facile metal-free polycondensation reaction between dicarbonyl derivative and dithioxamide for the synthesis of thiazolo[5,4-d]thiazole-based semiconductor polymer. We showed that the polymers obtained by classical Suzuki or Stille reactions and proposed metal-free polycondensation possess similar optoelectronic and physicochemical characteristics. Their application as hole-transport layers in perovskite solar cells (PSCs) showed that the polymer obtained by an alternative method provides comparable or even slightly higher performance of devices. These results illustrate availability of organic semiconductor materials via alternative green and sustainable polycondensation reaction for the state-of-the-art photovoltaic technologies.

The design of conjugated polymers with advanced properties is a significant task for the development of organic electronics. At the same time, it is important to pay attention to the methods of their synthesis, excluding toxic and expensive reagents, following the trends in sustainability. In this study, six thiazolothiazole-based conjugated polymers with thiophene, fluorene, phenylene, and benzodithiophene moieties were synthesized and thoroughly characterized. All materials were obtained through a non-catalyzed condensation reaction of carbonyl derivatives with rubeanic acid under ambient conditions. It is shown that the optoelectronic and electrophysical properties of polymers are suitable for their application in organic or hybrid electronic devices. The certain polymers are found to be promising hole-transport interlayer materials in perovskite solar cells, thus featuring the great potential of proposed methods of development of organic semiconductors.

Organic semiconductor small molecules (SMs) attract much attention to the design of various emerging photovoltaic and optoelectronic devices. High charge‐transport characteristics of SMs are important prerequisite for achieving outstanding performance of electronics. Herein, four promising SMs are investigated in terms of modulating charge‐transport properties by solvent engineering. It is shown that the hole mobility of thin films based on push–pull SMs can be effectively enhanced by the replacement of chlorobenzene with environmentally preferable hexane without changing a molecular structure of the compounds. As a result, 2–5 times higher hole mobility is achieved for hexane‐processed films that is attributed to the formation of favorable nanoscale morphology of films. This effortless approach can be applied to other organic semiconductor materials to precisely control the morphology and improve their electrophysical properties.

Our research presents novel TPA-based hole-transport materials with triisopropylsilyl side chains, which possess good alignment of HOMO energy level with MAPbI 3 increasing V OC of perovskite solar cells up to 1.1 V.

The synthesis of novel thiazolo[5,4-d]thiazole-containing conjugated polymer was performed by three alternative methods, namely, by the Stille or Suzuki cross-coupling as well as microwave-assisted condensation reaction with carbonyl precursor and dithioxamide. The latter way is straightforward and efficient for the design of novel materials with desirable optoelectronic and physicochemical characteristics providing an encouraging hole-transport properties and comparable performance of perovskite solar cells.

Hybrid organic-inorganic perovskite solar cells (PSCs) have drawn great attention in the past decade due to the rapid growth of their power conversion efficiency (PCE) and the advantage of their low-cost fabrication. The hole-transport materials (HTMs) play a crucial role in achieving high efficiency and operational stability of PSCs. In this work, we report the synthesis of two novel conjugated polymers by coupling of the alkylsilyl-substituted benzo[1,2-b:4,5-b']dithiophene unit with the thiophene-bridged pyrazine block and their investigation as dopant-free HTMs in n-i-p PSCs. The devices with polymer PBPyT-ex (poly[(4,8-bis(5-(triisopropylsilyl)thiophen-2-yl)-2,6-benzo[1,2-b:4,5-b']dithiophene)-alt-5,5'-(2,5-bis(4-(2-ethylhexyl)thiophen-2-yl)pyrazine)]) demonstrate PCEs up to 17.5%, outperforming the 14.9% efficiency of PSCs with PBPyT-in (poly[(4,8-bis(5-(triisopropylsilyl)thiophen-2-yl)-2,6-benzo[1,2-b:4,5-b']dithiophene)-alt-5,5'-(2,5-bis(3-(2-ethylhexyl)thiophen-2-yl)pyrazine)]), which is attributed to the difference in the quality of HTM films. The results obtained feature the combination of pyrazine, thiophene and benzodithiophene units as a successful example of polymeric HTM backbone design for PSCs with encouraging efficiency and high operational stability over 1500 h under continuous illumination.

Conjugated small molecules are advanced semiconductor materials with attractive physicochemical and optoelectronic properties enabling the development of next-generation electronic devices. The charge carrier mobility of small molecules strongly influences the efficiency of organic and hybrid electronics based on them. Herein, we report the synthesis of four novel small molecules and their investigation with regard to the impact of molecular structure and thermal treatment of films on charge carriers' mobility. The benzodithiophene-containing compounds (BDT) were shown to be more promising in terms of tuning the morphology upon thermal treatment. Impressive enhancement of hole mobilities by more than 50 times was found for annealed films based on a compound M4 comprising triisopropylsilyl-functionalized BDT core. The results provide a favorable experience and strategy for the rational design of state-of-the-art organic semiconductor materials (OSMs) and for improving their charge-transport characteristics.

Crystalline and liquid-crystalline conjugated small molecules represent a promising family of semiconductor materials for organic electronics applications. The control of the morphology and optoelectronic properties of small molecules allows tuning their charge transport characteristics and hence, improving the performance of electronic devices. Here, we designed four pentamers based on alternating thiophene and benzothiadiazole moieties and investigated the effect of their structure on the optoelectronic properties, ordering and charge transport characteristics. It is shown that thermal annealing of conjugated pentamers leads to remarkable changes in the microstructure and domain texture of thin films. As a result, an increase in hole mobility for compound M4 by one order of magnitude was achieved. These findings provide a valuable insight into the structure-property relationships for designed small molecules featuring them as promising semiconductor materials for further developing high-performance organic electronics.

New conjugated (BDT-TTBTBTT) n copolymers are featured as promising hole-transport materials for n–i–p perovskite solar cells delivering efficiencies of up to ∼19%.

Novel fluorene- and phenylene-based conjugated polymers with the TBTBT molecular framework consisting of the thiophene (T) and benzothiadiazole (B) building blocks have been synthesized and investigated. It has been demonstrated that the variation of X building blocks with branched side chains in (X-TBTBT)n-type structures, as well as the introduction of fluorine into the main chain, strongly affects the optical, electronic and physicochemical properties of the obtained polymers. The phenylene-based polymer with a fluorine- loaded TBTBT block achieves a power conversion efficiency of 7% in organic solar cells, which can be further improved by optimizing the active layer morphology.

Organic solar cells (OSCs) have attracted considerable attention in the last few decades due to their unique properties, including lightweight, flexibility, and manufacturing costs. Moreover, OSCs exhibit high performance under ambient light conditions revealing potential applications of these devices in low power electronics and Internet of Things (IoT) systems. In this work, we synthesized and characterized two novel conjugated polymers comprising thiazolothiazole, benzothiadiazole and thiophene alternating blocks with different thioalkyl substituents. Polymer P1 with 2-ethylhexylthio side chains provided power conversion efficiencies of ca. 5.0% on 4.5 cm(2) area OSCs fabricated using slot-die coating technique under ambient conditions. Furthermore, the assembled P1-based module delivered the power output of 45.5 mu W under 400 lx indoor illumination sufficient to power wireless air temperature sensor, thus demonstrating the potential of our devices for practical indoor applications.

Donor-acceptor conjugated polymers are considered advanced semiconductor materials for the development of thin-film electronics. One of the most attractive families of polymeric semiconductors in terms of photovoltaic applications are benzodithiophene-based polymers owing to their highly tunable electronic and physicochemical properties, and readily scalable production. In this work, we report the synthesis of three novel push–pull benzodithiophene-based polymers with different side chains and their investigation as hole transport materials (HTM) in perovskite solar cells (PSCs). It is shown that polymer P3 that contains triisopropylsilyl side groups exhibits better film-forming ability that, along with high hole mobilities, results in increased characteristics of PSCs. Encouraging a power conversion efficiency (PCE) of 17.4% was achieved for P3-based PSCs that outperformed the efficiency of devices based on P1, P2, and benchmark PTAA polymer. These findings feature the great potential of benzodithiophene-based conjugated polymers as dopant-free HTMs for the fabrication of efficient perovskite solar cells.

Perovskite solar cells (PSCs) currently reach high efficiencies, while their insufficient stability remains an obstacle to their technological commercialization. The introduction of hole-transport materials (HTMs) into the device structure is a key approach for enhancing the efficiency and stability of devices. However, currently, the influence of the HTM structure or properties on the characteristics and operational stability of PSCs remains insufficiently studied. Herein, we present four novel push-pull small molecules, H1-4, with alternating thiophene and benzothiadiazole or fluorine-loaded benzothiadiazole units, which contain branched and linear alkyl chains in the different positions of terminal thiophenes to evaluate the impact of HTM structure on PSC performance. It is demonstrated that minor changes in the structure of HTMs significantly influence their behavior in thin films. In particular, H3 organizes into highly ordered lamellar structures in thin films, which proves to be crucial in boosting the efficiency and stability of PSCs. The presented results shed light on the crucial role of the HTM structure and the morphology of films in the performance of PSCs.

Two conjugated polymers with (X-DADAD) n backbone and 2,6- or 4,8-linked benzobisthiazole (BBT) moieties were designed, synthesized and characterized as absorber materials in thin-film organic solar cells (OSCs). The 2,6-BBT polymer (P1) delivered enhanced short circuit densities and power conversion efficiencies in OSCs compared to devices based on 4,8-BBT polymer P2. Improved photovoltaic performance is related to the optimal morphology of P1/PC 71 BM blend films and higher and more balanced charge carrier mobilities.

Herein, the synthesis of two novel (X‐DADAD)n conjugated polymers comprising phenylene or fluorene X blocks coupled with benzothiadiazole acceptor (A) and thiophene donor (D) units is reported. The designed polymers are explored as absorber materials in organic solar cells and hole‐transport materials (HTMs) in perovskite solar cells (PSCs). The encouraging efficiencies of ≈17% are obtained in PSCs when using fluorene‐containing polymer P2 featuring this material as a promising HTM for the state‐of‐the‐art perovskite photovoltaics.

Herein, the synthesis of a novel isoindigo-based conjugated polymer using Suzuki and Stille polycondensation reactions is reported. It is shown that the polymer obtained using various reactions possesses different performance in photovoltaic devices. In particular, polymers synthesized using Suzuki and Stille polycondensation demonstrate 2.7% and 4.1% efficiency in organic solar cells, and 12.6% and 15.1% in perovskite solar cells, respectively. The observed difference in the performances of devices is attributed to the appearance of defects in the polymer obtained via Suzuki reaction. Using high-performance liquid chromatography it is demonstrated that the origin of the polymer quality deterioration is the poor stability of isoindigo-based monomer under conditions of Suzuki polycondensation. Revealing this aspect allows one to figure out a more effective approach for the synthesis of high-quality isoindigo-based polymers for organic electronics.

Conjugated polymers represent a promising family of semiconductor materials for thin-film organic solar cells (OSCs). An efficient approach to improve the photovoltaic performance of conjugated polymers is engineering the side chains attached to the polymer backbone. This work reports the impact of different alkyl substituents on the optoelectronic properties, charge carrier mobilities, thin film morphology, and photovoltaic performance of novel (X-DADAD)n conjugated polymers incorporating benzo[1,2-b:4,5-b']dithiophene moieties. It has been shown that loading conjugated polymers with appropriate alkyl side chains results in a spectacular performance improvement from 6.8% to 9% in OCSs using a model fullerene acceptor [6,6]-phenyl-C71 -butyric acid methyl ester. The obtained results feature side-chain engineering as a facile and efficient strategy for designing high-performance conjugated polymers for organic photovoltaics.

High efficiencies of organic solar cells (OSCs) are generally achieved for small-area devices processed from halogenated solvents, which are hazardous to human health and pollute the environment. Commercialization of OSCs requires the development of novel photovoltaic materials, which are suitable for large-scale fabrication of devices through printable techniques using environmentally-friendly solvents. In this work, we report the synthesis of two novel polymers comprising thiazolothiazole, benzothiadiazole (P1), and benzoxadiazole (P2) moieties and the fabrication of polymer-fullerene OSCs and photovoltaic modules by blade coating under ambient conditions. The P1-based solar cells and larger area modules showed tolerance to processing solvents and delivered encouraging efficiencies illustrating polymer P1 as a promising material for environment friendly large-area photovoltaics. (C) 2020 Elsevier Ltd. All rights reserved.

Two novel highly soluble bis(pyrrolidino)[60]fullerenes were synthesized and investigated as promising electron acceptor materials for organic solar cells. Reduced electron affinity of bis(pyrrolidino)[60]fullerenes as compared to the reference [60]PCBM enabled a spectacular increase in open-circuit voltage of organic bulk heterojunction solar cells by similar to 200 mV while using model P3HT and PCDTBT electron donor polymers. In addition to the improved optoelectronic properties, bis(pyrrolidino)[60]fullerenes were found to be resistant towards the photochemical cross-linking in contrast to conventional [60]PCBM and conjugated polymers. Most importantly, the designed fullerene derivatives efficiently suppressed photooxidation of conjugated polymers as revealed by ESR spectroscopy, which features a tremendous potential of applying these materials in the development of efficient and durable organic photovoltaics.

In view of a rapid development and increase in efficiency of organic solar cells, reaching their long-term operational stability represents now one of the main challenges to be addressed on the way toward commercialization of this photovoltaic technology. However, intrinsic degradation pathways occurring in organic solar cells under realistic operational conditions remain poorly understood. The light-induced dimerization of the fullerene-based acceptor materials discovered recently is considered to be one of the main causes for burn-in degradation of organic solar cells. In this work, it is shown that not only the fullerene derivatives but also different types of conjugated polymers and small molecules undergo similar light-induced crosslinking regardless of their chemical composition and structure. In the case of conjugated polymers, crosslinking of macromolecules leads to a rapid increase in their molecular weight and consequent loss of solubility, which can be revealed in a straightforward way by gel permeation chromatography analysis via a reduction/loss of signal and/or smaller retention times. Results of this work, thus, shift the paradigm of research in the field toward designing a new generation of organic absorbers with enhanced intrinsic photochemical stability in order to reach practically useful operation lifetimes required for successful commercialization of organic photovoltaics.