The Influence of Substrate and Top Electrode on the Crystallization Dynamics of P3HT: PCBM Blends

Substrate and top electrode effects on P3HT lamellar crystallization, were studied using the full device structure of a bulk-hetorojunction P3HT:PCBM organic solar cell, during thermal annealing. P3HT: PCBM chlorobenzene solutions (50 wt %) were spin coated on quartz, HMDS treated SiO2, SiO2/PEDOT: PSS, ITO/PEDOT: PSS. The structural evolution of these thick (∼100nm) films was probed during a realistic device-processing annealing cycle at 140°C for ∼53 minutes by time-resolved synchrotron Grazing Incidence X-Ray Diffraction (GI-XRD). The 20 nm- thick coated Aluminium layer on top of ITO/PEDOT: PSS/P3HT: PCBM acts as a nucleation site for the P3HT crystalline growth during annealing, increasing the number of the edge-on lamellae, and preferentially increasing the domain size of face on and edge-on lamellae, with minor growth of the randomly oriented lamellae.