Analysis of annealing process on P3HT:PCBM-based polymer solar cells using optical and impedance spectroscopy.

ABSTRACT

Thermal annealing is a well-known process for polymer solar cells because it improves the device characteristics. Especially, the carrier mobility and the light absorption of P3HTPCBM are significantly improved after the annealing process. Here, we examined the changes in the morphology of P3HTPCBM film according to the annealing temperature to find the changes during the thermal annealing process by measuring the optical absorption and X-ray diffraction. We also investigated the effect of two different annealing process (pre- and post-annealing) on the device performance of the standard polymer solar cells consisting of ITO/MoO3 (10 nm)/P3HTPCBM (150 nm)/LiF (0.5 nm)/Al (100 nm) by measuring current density-voltage and impedance characteristics. From the results, we found that the improvement in terms of the power conversion efficiency of the post-annealed device originated from the decrease of injection resistance between P3HTPCBM layer and Al electrodes.