Very high open-circuit voltage of 5.89 V in organic solar cells with 10-fold-tandem structure

Organic solar cells (OSCs) based on chloroaluminum phthalocyanine (ClAlPc) as donor and fullerene C60 as acceptor with a multi-tandem structure were fabricated. We demonstrated very high open-circuit voltage (VOC) and enhanced power conversion efficiency (PCE) for the multi-tandem OSCs. Using a fivefold structure, we obtained PCE of 2.49% with a VOC of 3.50 V, in comparison with PCE of ∼2% and VOC of 0.72–0.81 V for the single device. We also fabricated a tenfold-stacked OSC showing an extremely high VOC of 5.89 V. The multi-tandem OSCs with very high VOC have great potential for applications in limited-area low-power electronics.