An alternating copolymer of phenothiazine and ethylenedioxythiophene for perovskite solar cells: effects of flexible and rigid substituent alternation.

Developing p-type polymeric semiconductors with exceptional electrical performance, heat tolerance, and cost-effectiveness is pivotal for advancing the practical application of n-i-p perovskite solar cells. Here, we employed direct arylation polycondensation to synthesize an alternating copolymer of phenothiazine and 3,4-ethylenedioxythiophene, featuring a high glass transition temperature (175 °C). In addition to the alternation of conjugated units within the main chain, the copolymer features alternating flexible (2-octyldodecyl) and rigid (trimethylphenyl) substituents at the nitrogen positions of the phenothiazine moiety. Compared to reference polymers with solely flexible or rigid substituents, the alternating use of these moieties resulted in the polymeric semiconductor composite film with smoother morphology and enhanced hole mobility. By employing this polymer with a distinct distribution of substituents and an innovative main chain structure as a hole transport material, we fabricated perovskite solar cells achieving an average efficiency of 25.1%. These cells also exhibited excellent stabilities under conditions of 85 °C thermal storage and 45 °C operation.

Conjugated polymers of an oxa[5]helicene-derived polycyclic heteroaromatic: tailoring energy levels and compatibility for high-performance perovskite solar cells.

In the quest to enhance the efficiency and durability of n-i-p perovskite solar cells (PSCs), engineering hole-transporting conjugated polymers with well-matched energy levels, exceptional film-forming properties, rapid hole transport, and superior moduli is paramount. Here, we present a novel approach involving the customization of a conjugated polymer, designated as p-DTPF4-EBEH, comprising alternating units of an oxa[5]helicene-based polycyclic heteroaromatic (DTPF4) and 5,5'-(2,5-di(hexyloxy)-1,4-phenylene)bis(3,4-ethylenedioxythiophene) (EBEH), synthesized through palladium-catalyzed direct arylation. Relative to homopolymers p-DTPF4 and p-EBEH, p-DTPF4-EBEH demonstrates a proper HOMO energy level, hole density, and hole mobility, alongside superior film-forming capabilities. Remarkably, compared to the commonly used hole transport material spiro-OMeTAD, p-DTPF4-EBEH not only exhibits superior film-forming property and hole mobility but also offers increased modulus and improved waterproofing. Incorporating p-DTPF4-EBEH as the hole transport material in PSCs results in an average power conversion efficiency of 25.8%, surpassing the 24.3% achieved with spiro-OMeTAD. Importantly, devices utilizing p-DTPF4-EBEH demonstrate enhanced thermal storage stability at 85 °C, along with operational robustness.

Aza[5]helicene-Derived Semiconducting Polymers for Improved Performance in Perovskite Solar Cells: Exploring Energetic and Morphological Influences.

The strategic design of solution-processable semiconducting polymers possessing both matched energy levels and elevated glass transition temperatures is of urgent importance in the progression of thermally robust n-i-p perovskite solar cells with efficiencies exceeding 25 %. In this work, we employed direct arylation polymerization to achieve the high-yield synthesis of three aza[5]helicene-derived copolymers with distinct HOMO energy levels and exceptional glass transition temperatures. Upon integration of these semiconducting polymers into formamidinium lead triiodide-based perovskite solar cells, marked disparities in photovoltaic parameters manifest, primarily stemming from variations in the electrical conductivity and film morphology of the hole transport layers. The p-A5HP-E-POZOD-E copolymer, featuring a main chain comprising alternating repeats of aza[5]helicene, ethylenedioxythiophene, phenoxazine, and ethylenedioxythiophene, attains an initial average efficiency of 25.5 %, markedly surpassing reference materials such as spiro-OMeTAD (23.0 %), PTAA (17.0 %), and P3HT (11.6 %). Notably, p-A5HP-E-POZOD-E exhibits a high cohesive energy density, resulting in enhanced Young's modulus and diminished external species diffusion coefficients, thereby conferring perovskite solar cells with exceptional 85 °C tolerance and operational stability.

A Homopolymer of Xanthenoxanthene-Based Polycyclic Heteroaromatic for Efficient and Stable Perovskite Solar Cells.

Highly efficient perovskite solar cells typically rely on spiro-OMeTAD as a hole transporter, achieving a 25.7 % efficiency record. However, these cells are susceptible to harsh 85 °C conditions. Here, we present a peri-xanthenoxanthene-based semiconducting homopolymer (p-TNI2) with matched energy levels and a high molecular weight, synthesized nearly quantitatively through facile oxidative polymerization. Compared to established materials, p-TNI2 excels in hole mobility, morphology, modulus, and waterproofing. Implementing p-TNI2 as the hole transport layer results in n-i-p perovskite solar cells with an initial average efficiency of 24.6 %, rivaling 24.4 % for the spiro-OMeTAD control cells under identical conditions. Furthermore, the p-TNI2-based cells exhibit enhanced thermostability at 85 °C and operational robustness.

Molecular engineering of nitrogen-rich helicene based organic semiconductors for stable perovskite solar cells.

Polycyclic heteroaromatics play a pivotal role in advancing the field of high-performance organic semiconductors. In this study, we report the synthesis of a pyrrole-bridged double azahelicene through intramolecular oxidative cyclization. By incorporating bis(4-methoxyphenyl)amine (OMeDPA) and ethylenedioxythiophene-phenyl-OMeDPA (EP-OMeDPA) into the sp3-nitrogen rich double helicene framework, we have successfully constructed two organic semiconductors with ionization potentials suitable for application in perovskite solar cells. The amorphous films of both organic semiconductors exhibit hole density-dependent mobility and conductivity. Notably, the organic semiconductor utilizing EP-OMeDPA as the electron donor demonstrates superior hole mobility at a given hole density, which is attributed to reduced reorganization energy and increased centroid distance. Moreover, this organic semiconductor exhibits a remarkably elevated glass transition temperature of up to 230 °C and lower diffusivity for external small molecules and ions. When employed as the p-doped hole transport layer in perovskite solar cells, TMDAP-EP-OMeDPA achieves an improved average efficiency of 21.7%. Importantly, the solar cell with TMDAP-EP-OMeDPA also demonstrates enhanced long-term operational stability and storage stability at 85 °C. These findings provide valuable insights into the development of high-performance organic semiconductors, contributing to the practical application of perovskite solar cells.