Spiro-Bifluorene-Cored Dopant-Free Conjugated Polymeric Hole-Transporting Materials Containing Passivation Parts for...

Area of Science:

• Materials Science
• Organic Chemistry
• Photovoltaics

Background:

• Developing efficient and stable dopant-free hole transport materials (HTMs) is crucial for advancing perovskite solar cells (PSCs).
• Spiro-bifluorene derivatives offer a promising structural scaffold for HTMs due to their unique electronic and morphological properties.

Purpose of the Study:

• To synthesize and characterize two novel spiro-bifluorene-based dopant-free HTMs, X22 and X23.
• To evaluate their performance in perovskite solar cells and understand the structure-property relationships.

Main Methods:

• Facile condensation synthesis of spiro-bifluorene diamine with specific functionalized dichlorides (EDOT-5,7-dicarbonyl dichloride for X22 and 2,3,5,6-tetrafluoro-terephthaloyl dichloride for X23).
• Characterization of HTM properties including hole mobility and conductivity.
• Fabrication and testing of perovskite solar cell devices with the synthesized HTMs.
• Assessment of device stability under ambient conditions.

Main Results:

• X22 exhibited higher hole mobility (3.9 × 10^-4 cm² V^-1 S^-1) and conductivity (2.73 × 10^-4 S cm^-1) compared to X23 (1.4 × 10^-4 cm² V^-1 S^-1 and 2.39 × 10^-4 S cm^-1, respectively).
• The EDOT moiety in X22 improved the contact angle with the perovskite precursor solution to 24°, facilitating better interfacial contact.
• The X22-based PSC achieved a power conversion efficiency (PCE) of 19.18%, while the X23-based device reached 18.70%.
• Both devices showed good stability, retaining 86% (X22) and 79% (X23) of their initial PCE after 150 days.

Conclusions:

• Spiro-bifluorene-based HTMs with sulfur and oxygen heteroatoms (X22) enhance charge transport properties and perovskite interface interactions.
• The presence of heteroatoms (S, O, F) in HTM side chains is vital for defect passivation at the HTM/perovskite interface.
• The synthesized dopant-free HTMs offer a promising route towards efficient and stable perovskite solar cells.