Structural studies of the codeposited i -layer of ZnPc:C60 p -i -n solar cells

The nanostructure of the codeposited i ‐layer of zinc phthalocyanine (ZnPc):C60 p ‐i ‐n solar cells has been investigated, including the molecular orientation of ZnPc. The nanostructure of the i ‐layer was controlled by changing the substrate temperature during codeposition of ZnPc and C60. At a substrate temperature of 60 °C, a short‐circuit current density of 11.8 mA/cm2 and a power conversion efficiency of 2.7% are obtained under AM 1.5 simulated solar illumination at 100 mW/cm2. X‐ray diffraction reveals that ZnPc molecules form a regular π‐stacked structure in the i ‐layer. The π‐stacking direction is perpendicular to the hole transport direction in the i ‐layer thickness range from 150 to 300 nm. Therefore, the nanostructure of the codeposited i ‐layer is not necessarily suitable for hole transport to the electrode. However, the π‐stacking direction becomes parallel to the hole transport direction with increasing i ‐layer thickness from 300 to 900 nm. Thus, it is important to change the π‐stacking direction from perpendicular to parallel to the hole transport direction to increase the power conversion efficiency. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)