Ørnsø, Kristian Baruël1; García Lastra, Juan Maria3; De La Torre, Gema5; Rubio, Angel6; Thygesen, Kristian Sommer7
1 Center for Atomic-scale Materials Design, Center, Technical University of Denmark2 Department of Physics, Technical University of Denmark3 Department of Energy Conversion and Storage, Technical University of Denmark4 Atomic scale modelling and materials, Department of Energy Conversion and Storage, Technical University of Denmark5 Universidad Autónoma de Madrid6 Max Planck Institute for the Structure and Dynamics of Matter7 Center for Nanostructured Graphene, Center, Technical University of Denmark
An extensive database of spectroscopic properties of molecules from ab initio calculations is used to design molecular complexes for use in tandem solar cells that convert two photons into a single electron–hole pair, thereby increasing the output voltage while covering a wider spectral range. Three different architectures are considered: the first two involve a complex consisting of two dye molecules with appropriately matched frontier orbitals, connected by a molecular diode. Optimized combinations of dye molecules are determined by taking advantage of our computational database of the structural and energetic properties of several thousand porphyrin dyes. The third design is a molecular analogy of the intermediate band solar cell, and involves a single dye molecule with strong intersystem crossing to ensure a long lifetime of the intermediate state. Based on the calculated energy levels and molecular orbitals, energy diagrams are presented for the individual steps in the operation of such tandem solar cells. We find that theoretical open circuit voltages of up to 1.8 V can be achieved using these tandem designs. Questions about the practical implementation of prototypical devices, such as the synthesis of the tandem molecules and potential loss mechanisms, are addressed.