Electron-transporting third component modifying cathode for simplified inverted ternary blend solar cells†
Bathophenanthroline (Bphen), an electron transporting material widely used in organic light-emitting diodes, was added as a third component into a mixed solution of poly(thieno[3,4-b]-thiophene/benzodithiophene) (PTB7) and [6,6]-phenyl C71-butyric acid methyl ester (PC71BM) to fabricate simplified inverted polymer solar cells (PSCs). Bphen spontaneously migrated onto the ITO cathode during spin coating, and thereby formed a thin modifying interlayer between the cathode and the active layer. PSCs based on the ternary blend PTB7:PC71BM:Bphen showed a power conversion efficiency of 5.35%, higher than that of the binary blend PTB7:PC71BM in an inverted structure of ITO/photoactive layer/MoO3/Ag without an additional cathode-modifying interlayer (3.43%). The other electron transporting materials, 1,3,5-tris(2-N-phenylbenzimidazolyl)benzene (TPBI) and bathocuproine (BCP), were also confirmed to function as Bphen. This strategy simplifies the structure of inverted PSCs without significant loss in efficiency.