D-π-A-Type Pyrazolo[1,5-a]pyrimidine-Based Hole-Transporting Materials for Perovskite Solar Cells: Effect of the...

Area of Science:

• Materials Science
• Organic Chemistry
• Photovoltaics

Background:

• Donor-acceptor (D−A) small molecules are crucial as hole-transporting materials (HTMs) in perovskite solar cells (PSCs) due to their tunable optoelectronic properties.
• The reference material Spiro-OMeTAD is widely used but has limitations that necessitate the development of alternative HTMs.

Purpose of the Study:

• To design, synthesize, and characterize three novel isomeric D-π-A small molecules (PY1, PY2, PY3) for PSC applications.
• To evaluate their thermal stability, glass transition temperatures, hydrophobicity, and hole mobility.
• To assess their performance as doped HTMs in planar n-i-p PSCs and compare them with Spiro-OMeTAD.

Main Methods:

• Synthesis and characterization of three isomeric D-π-A small molecules with a pyrazolo[1,5-a]pyrimidine acceptor core and carbazole donor moieties.
• Measurement of thermal stability (Td), glass transition temperature (Tg), and hole mobility.
• Fabrication and testing of planar n-i-p PSCs using the synthesized molecules as doped HTMs.

Main Results:

• The synthesized molecules (PY1, PY2, PY3) exhibit suitable energy levels, high thermal stability (Td > 400 °C), molecular glass behavior (Tg 127–136 °C), and acceptable hydrophobicity.
• PY1 shows the highest hole mobility (3 × 10−6 cm2 V−1 s−1).
• PSC devices fabricated with PY1 achieved a power conversion efficiency (PCE) of 12.41%, comparable to Spiro-OMeTAD (12.58%). PY1-based devices also demonstrated improved stability.

Conclusions:

• The novel isomeric D-π-A small molecules, particularly PY1, are promising candidates for HTMs in PSCs.
• PY1 offers comparable performance and enhanced stability relative to Spiro-OMeTAD, potentially due to its hydrophobic nature.
• Further optimization could lead to even higher efficiencies and improved long-term stability in perovskite solar cells.