Structural studies of the codeposited i -layer of ZnPc:C60p -i -n solar cells

The nanostructure of the codeposited i -layer of zinc phthalocyanine (ZnPc):C60p -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 degree 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 Delta *p-stacked structure in the i -layer. The Delta *p-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 Delta *p-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 Delta *p-stacking direction from perpendicular to parallel to the hole transport direction to increase the power conversion efficiency. ([copy 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)