Open circuit voltage of stacked bulk heterojunction organic solar cells

We investigate the open circuit voltage (V-OC) of stacked bulk heterojunction (BHJ) organic solar cells based on conjugated polymer and fullerene derivative by spin-coating method. Poly[2-methoxy-5-(3',7'-dimethyloctyloxy)-1,4-phenylene vinylene] (MDMO-PPV) blended with [6, 6]-phenyl C-61-butyric acid methyl ester (PCBM) is used as a photoactive layer. The structure is ITO(lower BHJ cell)PEDOT:PSS/MDMO-PPV:PCBM/ITO/(upper BHJ cell)PEDOT:PSS/MDMO-PPV:PCBM/Al. V-OC of the stacked cell is 1.34 V and is about 1.6 times as large as that of single BHJ organic solar cell. V-OC of the stacked cell is not proportional to the number of photoactive layers, but is the sum of the V-OC values of the upper and the lower BHJ cells. (c) 2006 American Institute of Physics.