Predicting performance of an organic tandem solar cell: Effect of defect states density

In this present work, we report a study of a tandem organic solar cell that consists of two organic cells: poly [2,6-(4,4-bis(2-ethy1hexy1)-4H-cyc1openta[2,1-b;3,4-b '] dithiophene)-alt4,7(2,1,3-benzothiadiazole)] (PCPDTBTD): 1-(3-Methoxycarbonyl) propyl-l-phenyl [6], [6] C61 (PCBM) (as bottom cell) and (poly(3-hexyl)thiophene (P3HT): 1-(3-Methoxycarbonyl) propyl-l-phenyl [6], [6] C71 (PC70BM) (as top cell) stacked in series configuration. Thus, the effect of defect states density on the performances of the studied device is investigated with wx-AMPS software. We noticed that a high density of defect states can leads to the performances fall of the device. Therefore, the efficiency is decreased by 29.26% due to the increase of defect states density in bottom cell's active layer. Moreover, the obtained results were validated by those experimentally reported in literature. Indeed, the study of defect states density may have considered as an original approach for getting a predict view about real performances of a tandem organic solar cell. In addition, an optimization study on the thickness of the both active layers based the tandem cell device has been done, which a high efficiency of 7.06% is achieved for d
_PCPDTBT:PCBM
=190 nm and d
_P3HT:PC70BM
=150 nm.