Structural templating of chloro-aluminum phthalocyanine layers for planar and bulk heterojunction organic solar cells

Chloro-aluminum phthalocyanine (ClAlPc) film growth on 1H,1H,2H,2H-perfluorodecyltrichlorosilane (FDTS) and MoO3 is studied and correlated to ClAlPc/C-60 solar cell performance for both planar and bulk heterojunction (HJ) architectures. On top of unheated substrates, ClAlPc films grow amorphous independent of the substrate surface. When heated to 105 degrees C, ClAlPc grows with a face-on orientation on MoO3, with a crystalline phase I-like absorption profile. On FDTS, the film is optically characterized as phase II, and adopts an edge-on orientation. Implemented in planar HJ cells, the latter films show a substantially higher current compared to the other growth conditions, leading to 3% efficient cells. This current increase is investigated with spectral response and reflectivity measurements, and is found to be related to a more efficient exciton dissociation. Next, ClAlPc and C-60 are co-evaporated on FDTS and MoO3 modified ITO substrates to fabricate bulk HJ devices. Notably, we find that when a thin pure "templating" layer of ClAlPc is grown first, the subsequently grown ClAlPc: C-60 bulk HJ propagates the templating effect, and films show a higher crystallinity than without this templating layer, with higher fill factors as a result. On MoO3, this approach yields efficiencies above 4%. (C) 2011 Elsevier B. V. All rights reserved.