Optimization of small molecule organic solar cells based on Boron Subphthalocyanine Chloride (SubPc) and fullerene (C ₆₀ )

The small molecule organic solar cell based on Boron Subphthalocyanine Chloride (SubPc) and fullerene (C ₆₀ ) was fabricated. The structure of device is indium tin oxide (ITO)/SubPc (3∼21 nm)/C ₆₀ (30 nm)/2, 9-dimethyl-4, 7-diphenyl-1, 10-phenanthroline (BCP) (10 nm)/silver (Ag). The thickness of SubPc in device is varied from 3nm to 21nm to get the optimal thickness for the better performance. The maximum power conversion efficiency of 1.47% was obtained in the device at the SubPc thickness of 9 nm under 100 mW/cm ² AM1.5G illumination. The best performance of device at 9 nm SubPc layer is attributed to reach the optimal balance between the light absorption efficiency and the carrier collection efficiency in the device. In addition, the open-circuit voltage (Voc) maximum value of device is associated with the energy difference between the highest occupied molecular orbital (HOMO) of the donor and the lowest unoccupied molecular orbital (LUMO) of the acceptor, and the Voc of device is determined by difference of work function of electrodes. In order to increase the Voc of device, the Molybdenum Oxide (MoO ₃ ) layer was inserted between the ITO and the SubPc layer, resulting in the enhancement of Voc from 0.46V to 1V. As a result, the efficiency of device increased from 1.47% to 2.52%.