High-Performance Inverted Tandem Polymer Solar Cells Utilizing Thieno[3,4-c]pyrrole-4,6-dione Copolymer

We demonstrated the inverted solution processed tandem polymer solar cells, in which transparent pH-neutral poly(3,4-ethylenedioxylenethiophene)- polystylene sulfonic acid (PEDOT:PSS) and lithium zinc oxide layers were used as a recombination layer. We have used poly(di(2-ethylhexyloxy)-benzo[1,2-b:4,5-b']dithiophene-co-octylthieno[3,4-c]pyrrole-4,6-dione): [6,6]-phenyl-C-61 butyric acid methyl ester (PBDTTPD:PC61BM) and poly[(4,4'-bis(2-ethylhexyl)dithieno[3,2-b:2',3'-d] silole)-2,6-diyl-alt-(2,1,3-benzothiadiazole)-4,7-diyl]:[6,6]-phenyl-C-70 butyric acid methyl ester (PSETBT:PC70BM) as the active layers for front and rear subcells, respectively. The pH-neutral PEDOT:PSS/LZO serves as an electron- and hole-collecting and recombination layer. Our tandem solar cells showed a high open circuit voltage (V-oc) of 1.54 V, a short circuit current density (J(sc)) of 7.55 mA/cm(2), and a fill factor (FF) of 64.79% along with the power conversion efficiency of 7.53%. The V-oc value of our tandem solar cells is an ideal summation of V-oc values from front and rear subcells.