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

摘要

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-l-naphthyl-N',N'-diphe-nyl-1,1'-biphenyl-4,4'-diamine (NPB), 4,-4'-Bis(carbazol-9-yl) (CBP), 4,4',4"-tris(N-3-rnethylphenyl-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 ΔE_(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 ΔE_(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.