Perovskite solar cells (PSCs) have received considerable acclaim for their outstanding photovoltaic capabilities and cost-effectiveness. One of the major challenges, however, lies in the steep costs associated with charge transport materials. Traditional materials such as 2,2',7,7'-Tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene (Spiro-OMeTAD) are expensive and difficult to manufacture. As a result, there is an urgent need to identify inexpensive yet efficient alternatives to make PSC technology more economically attractive. Solving this challenge is key to accelerating the advancement of solar energy solutions and ensuring wider adoption. This study concentrates on the innovation of affordable hole transport materials that will help overcome the barriers to commercialization and push PSCs toward mainstream usage.

A team of researchers from Huaqiao University and Qufu Normal University have made a significant breakthrough in solar energy research. In their recent publication (DOI: 10.26599/EMD.2024.9370036), which appeared in *Energy Materials and Devices* in June 2024, they introduced three new hole transport materials designed for n-i-p PSCs that could radically enhance efficiency levels. These materials, carefully developed and synthesized, exhibit remarkable characteristics, with the potential to elevate solar cell performance beyond today's most common standards—a hopeful leap forward in the quest for viable renewable energy solutions.

The study unveils three novel, cost-effective hole transport materials (HTMs)—4,4'-(3,3'-bis(4-methoxy-2,6-dimethylphenyl)-[2,2'-bithiophene]-5,5'-diyl)bis(N,N-bis(4-methoxyphenyl)aniline) (TP-H), 4,4'-(3,3'-bis(4-methoxy-2,6-dimethylphenyl)-[2,2'-bithiophene]-5, 5'-diyl)bis(3-methoxy-N,N-bis(4-methoxyphenyl)aniline) (TP-OMe), and 4,4'-(3,3'-bis(4-methoxy-2,6-dimethylphenyl)-[2,2'-bithiophene]-5,5'-diyl)bis(3-fluoro-N,N-bis(4-methoxyphenyl)aniline) (TP-F)—all featuring a bithiophene core. These molecules are tailored to improve crystallinity and solubility, which are critical for efficient charge transport in PSCs. Notably, TP-F reached a power conversion efficiency (PCE) exceeding 24%, owing to the inclusion of fluorine atoms that improved molecular packing, lowered the highest occupied molecular orbital (HOMO) energy level, and significantly enhanced both hole mobility and electrical conductivity. This improvement consequently reduced defect densities and suppressed recombination losses, ensuring superior overall performance in solar cells. Such work underscores the value of the 3,3'-bis(4-methoxy-2,6-dimethylphenyl)-2,2'-bithiophene core in leading to cost-efficient HTMs and highlights considerable strides towards making PSCs more commercially viable.

Dr. Wei Gao, the lead researcher of the study, expressed, "The development of these innovative HTMs is a key advancement in making PSCs more attractive for industrial-scale production. With these new materials offering enhanced efficiency and lower costs, we may see accelerated adoption of PSCs in the global solar market, driving more sustainable, cost-effective energy alternatives."

The findings from this research have far-reaching potential, as they pave the path for large-scale production of affordable and high-performance PSCs. The successful implementation of TP-F in PSC manufacturing demonstrates the possibility of significantly reducing production costs while maintaining superior operational efficiency. This landmark could drive more widespread integration of solar technologies, lending support to global efforts in fostering sustainable energy and gradually reducing the world's dependence on fossil fuels.

This research was made possible thanks to financial support from the National Natural Science Foundation of China (Grant Nos. U23A20371, U21A2078, and 22179042), the Natural Science Foundation of Fujian Province (Grant No. 2023J06034), the Natural Science Foundation of Xiamen, China (Grant No. 3502Z20227036), and the Scientific Research Funds of Huaqiao University (Grant No. 605-50Y23024).

About Energy Materials and Devices

*Energy Materials and Devices* is a quarterly journal launched by Tsinghua University and made available through SciOpen. The journal is committed to promoting international, peer-reviewed, and open-access research at the forefront of energy material development. The journal encompasses the entire research and industrialization pipeline, featuring original, groundbreaking work on the design, synthesis, and characterization of materials for energy storage and conversion devices, among other topics.

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Journal

Energy Materials and Devices

DOI

10.26599/EMD.2024.9370036

Article Title

Bithiophene-based cost-effective hole transport materials for efficient n–i–p perovskite solar cells

Article Publication Date

31-May-2024