Benzothiadiazole-based polymer for single and double junction solar cells with high open circuit voltage

Area of Science:

• Materials Science
• Organic Electronics
• Photovoltaics

Background:

• Developing efficient organic solar cells (OSCs) is crucial for renewable energy.
• Tuning the morphology of polymer-fullerene blends impacts device performance.
• High open-circuit voltage (Voc) is a key parameter for efficient solar cells.

Purpose of the Study:

• To investigate the effect of fullerene loading on the structural and morphological properties of PBT-T1:fullerene blends.
• To optimize the blend ratio and processing additives for enhanced photovoltaic performance.
• To fabricate high open-circuit voltage single and tandem junction solar cells.

Main Methods:

• Fabrication of single and tandem junction solar cells using PBT-T1 blended with fullerene derivatives (PC60BM, PC70BM).
• Structural and morphological characterization using X-ray diffraction (XRD) and atomic force microscopy (AFM).
• Device performance evaluation, including open-circuit voltage, short-circuit current density, fill factor, and power conversion efficiency.
• Charge carrier mobility and density measurements using Photo-charge extraction by linearly increasing voltage (Photo-CELIV).

Main Results:

• Higher fullerene ratios led to smaller disordered polymer domains, improving performance.
• An optimal PBT-T1:PC60BM ratio of 1:2 provided adequate charge transport.
• Addition of 1,8-diiodooctane (DIO) significantly enhanced short-circuit current density and fill factor.
• Single junction cells achieved up to 5.65% efficiency with high Voc (~0.9 V).
• Tandem cells reached 5.2% efficiency with a high Voc of 1.62 V.

Conclusions:

• Morphological control through fullerene loading and processing additives is critical for high-performance organic solar cells.
• The PBT-T1:PC60BM system, particularly with DIO additive and optimized ratios, shows promise for efficient photovoltaic applications.
• The study demonstrates a viable strategy for achieving high open-circuit voltage in both single and tandem junction organic solar cells.