| Organic photovoltaic technology based on conjugated polymers or small organic functional molecules, has attracted considerable attention in last two decades owing to their potential to provide flexible, lightweight, and environmentally friendly solar cells. The use of bulk heterojunction solar cells, consisting of a penetrating donor acceptor molecules within a cheap inorganic porous TiO2 matrix, is considered as one of the most promising and cost-effective approaches. However, in order to achieve a high efficiency, solar cells must absorb photons in a broad spectrum. Specifically, broad band light absorbers are needed for near infrared absorption, cell designs or materials that increase the interface area of donor-acceptor materials in the heterojunctions to provide effective exciton disassociation, and to reduce optical interference. The goal of this work was to develop cost effective organic bulk heterojunction solar cells. In order to accomplish this goal, the following objectives were established: (1) study the optical properties of the donor and acceptor materials; (2) fabricate a TiO2 matrix to increase the number of donor and acceptor molecules and reduce light interference; (3) study the surface morphology of the TiO2 films and the active layers; and (4) fabricate and characterize organic solar cells using the studied materials. The bulk heterojunction solar cells were fabricated with rare earth phthalocyanine double or triple deckers as electron donors with a perylenediimide derivative as electron acceptor. Two-types of cells with and without a TiO2 spacer layers were fabricated. The cells fabricated with the triple-decker donor had the best efficiency (0.36%), which was attributed to its strong UV-Visible and near infrared absorption and its strong pi-pi interactions between Pc planes for electron delocalization and charge transport. The photoelectric performance of double- and triple-decker photovoltaic cells was highly dependent on the decker structures, the morphology of the active layers, and the cell structures. Future work should address cell efficiency improvement from 0.36% to 4% to make this type of cell commercially valuable. |
