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Microfluidic technologies are highly adept at generating controllable compositional gradients in fluids, a feature that has accelerated the understanding of the importance of chemical gradients in biological processes. That said, the development of versatile methods to generate controllable compositional gradients in the solid‐state has been far more elusive. The ability to produce such gradients would provide access to extensive compositional libraries, thus enabling the high‐throughput exploration of the parametric landscape of functional solids and devices in a resource‐, time‐, and cost‐efficient manner. Herein, the synergic integration of microfluidic technologies is reported with blade coating to enable the controlled formation of compositional lateral gradients in solution. Subsequently, the transformation of liquid‐based compositional gradients into solid‐state thin films using this method is demonstrated. To demonstrate efficacy of the approach, microfluidic‐assisted blade coating is used to optimize blending ratios in organic solar cells. Importantly, this novel technology can be easily extended to other solution processable systems that require the formation of solid‐state compositional lateral gradients., The authors would like to acknowledge financial support from the Spanish Ministry of Economy, Industry and Competitiveness through the “Severo Ochoa” Programme for Centers of Excellence in R&D (SEV‐2015‐0496) and project reference PGC2018‐095411‐B‐I00 as well as the European Research Council (ERC) under grant agreement no. 648901. J.P.‐L. acknowledges the European Research Council Starting Grant microCrysFact (ERC‐2015‐STG No. 677020) and the Swiss National Science Foundation (200021_181988) and ETH Zürich. R. R.‐T. acknowledges the support from Generalitat de Catalunya and the COFUND programme of the Marie Curie Actions of the 7th R&D Framework Programme of the European Union (BP‐B 00256). X.R.‐M. acknowledges the departments of Physics, Chemistry and Geology of the Autonomous University of Barcelona (UAB) as coordinators of the PhD programme in Materials Science. X.R.‐M. and C.F. acknowledge Nicole Kleger‐Schai from ETH Zürich for her valuable help in using the rheometer. X.R.‐M. and M.C.‐Q. acknowledge Dr. Joan M. Cabot from the University of Tasmania for fruitful discussions on 3D printing. D.B.A. thanks the University of Nottingham Beacon Propulsion Futures.

One of the major bottlenecks in the development of organic photovoltaics is the time needed to evaluate each material system. This time ranges from weeks to months if different variables such as blend composition, thickness, annealing, and additives are to be explored. In this study, the use of lateral gradients is proposed in order to evaluate the photovoltaic potential of a material system up to 50 times faster. A platform that combines blade coating using controllable velocity profiles (thickness gradients) with multichannel dispensers (composition gradients) and controlled lateral annealing variations (nanostructure gradients) is introduced. These samples are then analyzed using photocurrent and Raman imaging in order to correlate one to one the device performance, thickness, composition, and annealing temperature. The strength of the developed technology is shown by optimizing three different systems, namely PCDTBT:PC70BM, PTB7‐Th:PC70BM, and PffBT4T‐2OD:PC70BM, obtaining efficiencies ≈5%, 8%, and 9.5%, respectively, using less than 10 mg of each polymer in the process., The authors are indebted to Dr. Bernhard Dörling for the development of the blade coating accelerating electronics, and Xavier Tejero and Prof. Alejandro Goñi for their help with setting up the LBIC system. The authors would also like to thank Dr. Juan Cabanillas (IMDEA) for useful discussions. The authors would like to acknowledge financial support from the Ministerio de Economía y Competitividad of Spain through the “Severo Ochoa” Programme for Centres of Excellence in R&D (SEV‐2015‐0496) and project MAT2015‐70850‐P; and the European Research Council (ERC) under grant agreement No. 648901.