High Throughput Screening of Composition in Multicomponent Organic Based Photovoltaics

Combining two acceptors and one donor in the active layer of organic solar cells, also referred to as ternary blending, has become a very important strategy in this field in order to improve light harvesting, as well the preventing morphological evolution. The efficiency strongly depends on the exact ternary composition, as the optimum mixing will be a compromise between transport and optical properties. Despite its importance, predicting how the final efficiency of a system depends on composition has been, thus far, elusive [1].<br/>In this talk, we will first describe a novel methodology for the fast evaluation of binary and ternary systems for photovoltaics. The new approach is based on the fabrication of samples with gradients in the relevant parameters of interest that represent a large fraction of the corresponding parameter space. In particular, we fabricate gradients in thickness, microstructure, and composition, and apply hyperspectral imaging to correlate material and device properties [1]. Then, we will show how this machinery, which is ca 100 faster than conventional optimization protocols [2], can be used to cartograph the complex composition phase diagram for ternary organic solar cells based on a single polymer donor (such as P3HT, PTB7-Th or PM6) and two acceptors (e.g. IDTBR, IDFBR, Y6, ITIC, PCBM, etc.) [3,4]. We find that, depending of the specific system, the ternary land scape can exhibit either one or more efficiency maxima. We also observe that the optimum composition is often found outside the 1:1 donor:acceptor ratio trajectory. Finally, we will discuss different options to choose the third material in the ternary, including the use of an experimental genetic algorithm method that we have developed.<br/><br/>[1] Predicting the photocurrent–composition dependence in organic solar cells, X. Rodríguez-Martínez, E. Pascual-San-José, Z. Fei, M. Heeney, R. Guimerà, M. Campoy-Quiles, <i>Energy & Environmental Science</i> 14, 986 (2021).<br/>[2] Accelerating organic solar cell material’s discovery: high-throughput screening and big data,<br/>X. Rodríguez-Martínez, E. Pascual-San-José, M. Campoy-Quiles, <i>Energy & Environmental Science</i>, 14, 3301 (2021)<br/>[3] Efficient exploration of the composition space in ternary organic solar cells by combining high-throughput material libraries and hyperspectral imaging, A. Harillo-Baños, X. Rodríguez-Martínez and M. Campoy-Quiles, <i>Advanced Energy Materials</i>, 10, 1, 1902417 (2020).<br/>[4] Suppressing CoCrystallization of Halogenated NonFullerene Acceptors for Thermally Stable Ternary Solar Cells, S. Hultmark, et al, Advanced Functional Materials, 30, 2005462 (2020).