Highly efficient photovoltaic cells based on a bulk heterojunction configuration composed of C70 with various donor materials at 5 wt. % donor concentration were fabricated. The tetraphenyldibenzoperiflanthene (DBP) donor achieved the highest power conversion efficiency (ηPCE) of 6.4% for the optimized cell. The improved performance with DBP arises from a combination of a higher absorption coefficient than 1,1-bis-(4-bis(4-methyl-phenyl)-amino-phenyl)-cyclohexane and a symmetrical molecular structure. The high ηPCE with only 5 wt. % donor is attributed to a sufficient donor concentration for enhanced Frenkel exciton dissociation in C70, while efficiency and electron mobility decrease at higher donor concentrations.

We demonstrate enhanced power conversion efficiency (ηPCE) for small molecular-based organic photovoltaic cells with an exciton blocking layer (ExBL) at the anode/donor interface. Although poly(3,4-ethylenedioxythiophene):poly(4-styrene sulfonate) (PEDOT:PSS) films are widely used as anodic buffer layers, they also act as exciton quenchers. To prevent exciton quenching, we introduced a tris[4-(5-phenyl thiophen-2-yl)phenyl]amine layer between the donor and the PEDOT:PSS layer and clarified its effect. By a combination of dual ExBLs at both the anode and cathode sides, we achieved significantly enhanced short circuit current and ηPCE values; the highest ηPCE = 5.24% was obtained by optimizing the device parameters.

No abstract

To enhance the performance of organic photovoltaic (OPV) cells, preparation of organic nanometer-sized pillar arrays is fascinating because a significantly large area of a donor/acceptor heterointerface having continuous conduction path to both anode and cathode electrodes can be realized. In this study, we grew cupper phthalocyanine (CuPc) crystalline nanopillar arrays by conventional thermal gradient sublimation technique using a few-nanometer-sized trigger seeds composed of a CuPc and 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) stacked layer. We optimized the pillar density by tuning crystal growth condition in order to apply it to OPV cells.