The influence of donor material on achieving high photovoltaic response for organic bulk heterojunction cells with small ratio donor component

Abstract Authors demonstrated impact of series small ratio donors in C 60 matrix on photovoltaic (PV) performance. A series of donor materials such as N′,N′-Di-1-naphthyl-N′,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB), 4,-4′-Bis(carbazol-9-yl) (CBP), 4,4′,4″-tris(N-3-methylphenyl-N-phenyl-amine)triphenyl-amine (m-MTDATA), copper phthalocyanine (CuPc) and 4,4,4-tris(n-carbazolyl-triphenyl-amine) (TCTA) were blended with fullerene (C 60 ) by different ratio. It was found that although donor–acceptor (DA) interface in planar heterojunction (PHJ) structure increased charge separation probability at the near interface section, the PV response was stronger for bulk heterojunction (BHJ) with low-ratio donor doping into C 60 matrix in which exciton dissociation can take place immediately after photon absorption without a diffusion progress. The power conversion efficiency (PCE) of BHJ-PV cell based on NPB donor reaches 2.25%, which is double of that of the PHJ cell. In terms of our series results we obtained that Δ E HOMO (HOMO C60 –HOMO donor ) between C 60 acceptor and donors would provide a maximal influence on achievement of a maximal PCE and an optimal Δ E HOMO locates around 0.8 eV, which implies that dissociation of photo-exciton at C 60 matrix needs feasible driving force. More detail mechanism was also argued.