Influence of organic salt concentration on the performance of bulk heterojunction organic solar cell

The effect of organic salt on the performance of bulk heterojunction organic solar cell was investigated by varying the concentration of tetrabutylammonium hexafluorophosphate (TBAPF₆). Organic solar cells based on TBAPF₆-blended poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEHPPV): (6,6)-phenyl-C61 butyric acid methyl ester (PCBM) thin films with aluminium (Al) as cathode have been fabricated on ITO substrates. The MEHPPV:PCBM films with different concentrations of TBAPF₆ (10, 20, 30 and 40 wt% with respect to MEHPPV) were deposited onto the ITO by spin coating technique, followed by deposition of Al using electron gun evaporation technique to build the devices. Experimental results showed that the short circuit current density and open circuit voltage improved with increasing of TBAPF₆ concentration up to 20 wt% since more dissociated ions accumulated at the photoactive layer-electrode interfaces resulted in higher built in electric field. However, the short circuit current density and open circuit voltage started to decrease at TBAPF₆ concentration of 30 wt%, indicating higher charge recombination as a result of agglomeration of TBAPF₆.