Efficient Semitransparent Solar Cells with High NIR Responsiveness Enabled by a Small-Bandgap Electron Acceptor.

Area of Science:

• Organic Photovoltaics (OPVs)
• Materials Science
• Semiconductor Physics

Background:

• Commercialization of OPVs is advancing due to improved power conversion efficiency (PCE).
• Semitransparent OPVs (STOPVs) offer value-added applications like energy-harvesting windows.
• Current STOPVs using fullerene acceptors have limited PCE (4-6%) due to trade-offs between light absorption and transparency.

Purpose of the Study:

• To develop a novel small-bandgap electron-acceptor material (ATT-2) for enhanced light harvesting.
• To improve the PCE and transparency of single-junction STOPVs.
• To address the challenge of harvesting more photons in the UV-vis-NIR region without sacrificing device transparency.

Main Methods:

• Synthesis and characterization of a new small-bandgap electron-acceptor material, ATT-2.
• Fabrication of organic photovoltaics (OPVs) by combining ATT-2 with PTB7-Th.
• Performance evaluation of as-cast OPVs and proof-of-concept STOPVs, measuring PCE, transparency, open-circuit voltage, and short-circuit current.

Main Results:

• ATT-2 exhibits strong near-infrared (NIR) absorption (600-940 nm) with an optical bandgap (E_g^opt) of 1.32 eV.
• As-cast OPVs achieved a PCE of up to 9.58%, with a fill factor of 0.63, open-circuit voltage of 0.73 V, and short-circuit current of 20.75 mA cm^-2.
• Proof-of-concept STOPVs demonstrated a record PCE of 7.7% for single-junction devices with 37% transparency, attributed to complementary absorption between PTB7-Th and ATT-2 in the NIR region.

Conclusions:

• The novel ATT-2 material significantly enhances NIR absorption, leading to higher photocurrent in OPVs.
• The developed STOPVs achieve a leading PCE and transparency balance, showcasing the potential for efficient energy-harvesting windows.
• This work presents a promising strategy for advancing single-junction STOPV technology through tailored small-bandgap acceptor materials.