P3HT/PCBM bulk heterojunction organic photovoltaics: correlating efficiency and morphology

Area of Science:

• Materials Science
• Polymer Science
• Renewable Energy

Background:

• Optimizing polymer-based photovoltaic (PV) devices relies on controlling thin film morphology.
• The active layer's morphology and interfacial behavior are critical for device performance.

Purpose of the Study:

• To investigate the influence of preparation conditions on thin film morphology and interfacial behavior.
• To describe morphology development in P3HT:PCBM mixtures under different confinement and annealing conditions.

Main Methods:

• Small angle neutron scattering (SANS)
• Electron microscopy
• Thermal treatment (annealing) under confinement (Al cathode) or unconfined conditions

Main Results:

• A nanoscopic, bicontinuous morphology forms rapidly (seconds) at 150 °C and coarsens slightly with extended annealing.
• High miscibility and rapid interdiffusion observed between P3HT and PCBM.
• Preferential segregation of components to electrode interfaces (PEDOT-PSS anode, Al cathode).

Conclusions:

• Preparation conditions, particularly thermal treatment and confinement, strongly influence thin film morphology.
• Morphology development, including interdiffusion and segregation, is directly linked to the efficiency of polymer PV devices.