A tandem solar cell device whose sub-cells are fabricated exclusively from small molecules (SMs) through both solution-processed and vacuum-processed deposition techniques is described. The front sub-cell's active layer consists of a bulk heterojunction (BHJ) DPP(TBFu)2:PC70BM device while the back cell has a typical bilayer structure employing a 2,4-bis[4-(N,N-diisobutylamino)-2,6-dihydroxyphenyl] squaraine (SQ) donor and a C60 acceptor.
