Influence of tetrabutylammonium hexafluorophosphate doping on the performance of single layer bulk heterojunction organic solar cells

Organic solar cells have attracted considerable interest due to their great potential for the production of flexible and large-area solar cells at relatively low costs and easy-processing fabrication properties [1-2]. The present work reports the effect of organic salt, tetrabutylammonium hexafluorophosphate (TBAPF₆) doping on the performance of single layer bulk heterojunction organic solar cell with ITO/MEHPPV:PCBM/Al structure where indium tin oxide (ITO) was used as anode, poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEHPPV) as donor, (6,6)-phenyl-C61 butyric acid methyl ester (PCBM) as acceptor and aluminium (Al) as cathode. The active layer was prepared by spin coating technique. The organic solar cells were characterized by current-voltage measurements under illumination with a halogen projector lamp at 100 mW/cm² using Keithley 237 source measurement unit. As shown in Fig.1, the device doped with TBAPF₆ demonstrated a significant increment in the short circuit current density, J_sc and open circuit voltage, V_oc as compared to the undoped device. Under illumination of a halogen projector lamp at 100 mW/cm², the undoped device showed a J_sc of 0.54 μA/cm², V_oc of 0.24 V, and a fill factor (FF) of 16%. With the doping of TBAPF₆, the J_sc increased almost ten times to 6.41 μA/cm². Besides, the V_oc also improved significantly from 0.24 V to 0.50 V. The significant improvement was attributed to the increase of built-in electric field caused by accumulation of ionic species at the electrode/active layer interfaces. Therefore, TBAPF₆ doping has been shown to be a simple and cost-effective approach to increase the performance of organic solar cell.