Effects of buffer layers on properties of bulk hetero junction flexible organic solar cells

We fabricated the flexible organic solar cells (OSCs) using the alternating co-polymer, poly[N-9″-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole) (PCDTBT) in bulk hetero junction composites with the fullerene derivative [6,6]-phenyl C61-butyric acid methyl ester (PCBM) active layer for the electron donor and acceptor materials, respectively. The active layer was spin-coated onto various substrates with different buffer layers of lithium fluoride (LiF) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) on the indium tin oxide (ITO) coated polyethylene naphthalene (PEN) substrates, such as PEN/ITO/LiF, PEN/ITO/PEDOT:PSS and PEN/ITO/PEDOT:PSS/LiF. The effects of the buffer layer position on the electrical and morphological properties of the devices were investigated. The performance of OSCs coated on the PEN/ITO/PEDOT:PSS/LiF substrate exhibited the best electrical property among the prepared samples, showing the maximum short circuit current, open circuit voltage, fill factor and power conversion efficiency values were about 11.4 mA/cm2, 0.90 V, 39.3 % and 4.0 %, respectively.