Bulk-heterojunction photovoltaic devices based on donor–acceptor organic small molecule blends

We present a systematic study on photovoltaic devices that combine an organic small molecule photoactive donor–acceptor bulk heterojunction system with controlled doping of the charge transport layers. The doped transport layers are formed using high vacuum co-evaporation deposition technique (i.e. co-sublimation of matrix and dopant). Solar cell devices have been fabricated based on zinc-phthalocyanine (ZnPc) as donor (D) and fullerene (C₆₀) as electron acceptor (A) with doped charge transport layers. The cells show a short circuit current, I_sc=1.5 mA/cm², an open circuit voltage, V_oc=450 mV, a fill factor, FF=0.5, and a power conversion efficiency, η_e=3.37% under sun (10 mW/cm²) white light illumination. In addition, these bulk-heterojunction photovoltaic devices were characterized under 1 sun (100 mW/cm²) white light illumination showing I_sc=6.3 mA/cm², V_oc=500 mV, and η_e=1.04%. We have observed that the performance of such ‘bulk-heterojunction’ photovoltaic devices is critically dependent on the transport properties of the interpenetrating network D/A system and doped charge transport layers.