Active layer analysis of interpenetrating heterojunction organic thin-film solar cells by X-ray photoelectron spectroscopy

• Gradual change of active layer of organic solar cell from P3HT to C60.
• The interpenetrating heterojunction structure possesses a complicated interface.
• The donor-acceptor interface was formed by rod-shaped C60 particles and grains.

The active layer analysis of interpenetrating heterojunction organic thin-film solar cells by X-ray photoelectron spectroscopy (XPS) has been studied. The interpenetrating heterojunction structure based on poly(3-hexylthiophene) (P3HT) and fullerene (C60) could be fabricated by spin-coating P3HT onto a deposited C60 film. The composition ratios of P3HT and C60 in the interpenetrating heterojunction active layer in the depth direction and the interface morphology between the P3HT and C60 layers have been clarified by XPS with argon ion etching and scanning electron microscopy. It has been found that the donor–acceptor interface of the interpenetrating heterojunction active layer is formed by the rod-shaped C60 particles with a width of approximately 100 nm and C60 grains with a size of 10–50 nm.