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

Authors demonstrated impact of series small ratio donors in C₆₀ 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 (C₆₀) 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 C₆₀ 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 ΔE_HOMO (HOMO _C60-HOMO_donor) between C₆₀ acceptor and donors would provide a maximal influence on achievement of a maximal PCE and an optimal ΔE_HOMO locates around 0.8 eV, which implies that dissociation of photo-exciton at C₆₀ matrix needs feasible driving force. More detail mechanism was also argued. © 2013 Elsevier B.V. All rights reserved.