Fig. Overview of the discovery of new materials for tandem OSCs process. In step 1, the fitness function is developed to predict the PCE using an ensemble of random forest and a neural network. In step 2, three GAs are used to discover various types of NFAs, such as fused, fused with π-bridges, and unfused NFAs. In step 3, a GA found new donor polymers that work well with many of the NFAs found in step 2. In the last step, a GA is used to find optimal combinations of acceptor and donor materials to maximize absorbance and minimize spectral overlap. that there are better candidates within the search space, however they have not been found due to the stochastic nature of the GA. We are currently studying the impact of GA hyperparameters and convergence criteria in efficiently searching the chemical space, which will be published separately. The massive speedups of using GAs to efficiently screen chemical space compared to brute-force high-throughput screening approaches can be seen in Table . The largest search space is ca. 23 billion NFAs for unfused NFAs, and the GA only had to examine 434 NFAs before converging on a high performer. This yielded a speedup of 5.3 × 10 7 compared to an exhaustive search approach. Units frequently selected in the GAs were then analyzed to gain insight into the chemical design rules (Fig. ). For terminal units, unit 39 appeared in over 65% of NFAs, especially the high-performing ones. This unit, norborenyl-fused 1,1dicyanomethylene-3-indanone, also known as CBIC, is a 3-D nonaromatic polycylic terminal group. This unit has shown promise in NFAs such as LL2 , with its unique 3D end group. Singlecrystal analysis of CBIC has shown that they form anti-parallel dimers that prevent the formation of large aggregates and improve solubility . The other top terminal units (ESI Fig. ) mostly contain 1,1-dicyanomethylene-3-indanone with various halogen substituents. Halogenation has proven to be an effective strategy for tuning energy levels, optical band gaps, and intermolecular stacking. Chlorination has been shown to induce stronger red-shift absorption, decrease exciton binding energy, decrease the singlet-triplet gap, and increase the total oscillator strengths compared to fluorination . Bromination can also lead to stronger intermolecular interactions and broader absorption compared to fluorination and chlorination .