Owing to the recently developed nonfullerene small molecule acceptors, the best power conversion efficiency (PCE) of solution-processable organic solar cells (OSCs) has been boosted up to over 12%, which makes this technology an economically viable contender for commercialization. Along with the steady progress in PCE achieved by spin-coating photovoltaic materials with chlorinated solvents in protective atmosphere, a central issue in the development of OSCs is pursuing a greener and simpler manufacturing protocol, which particularly allows for large-area processing in ambient air. Particularly, it is still a great challenge to replace halogenated solvents with halogen-free, low-toxicity solvents to achieve high-efficiency nonfullerene OSCs.
Here we show that ~11.6% efficiency is achieved in nonfullerene OSC device based on PBDB-T:IT-M by using a non-halogenated solvent combination. Moreover, the device parameters were correlated to the morphology investigated by synchrotron radiation grazing-incidence wide-angle X-ray scattering (GIWAXS), resonant soft X-ray scattering (R-SoXS), and differential scanning calorimetry (DSC). We observed a monotonic correlation between the average composition variations and photovoltaic device characteristics across all processing protocols in this record-efficiency material system. This correlation is indeed universal for OSC, irrespective of acceptor materials used (fullerenes, nonfullerene molecular acceptor, or conjugated polymers) and fabrication methods used (spin-coating or blade-coating).[1-5] We believe this nonhazardous solvent approach will be also applicable in the large area roll-to-roll coating and industrial scale printing of high-efficiency OSCs in air.
 Li, S.; Ye, L.; Zhao, W.; Zhang, S.; Mukherjee, S.; Ade, H.; Hou, J., Energy-Level Modulation of Small-Molecule Electron Acceptors to Achieve over 12% Efficiency in Polymer Solar Cells. Adv. Mater. 2016, 28 (42), 9423-9429.
 Ye, L.; Xiong, Y.; Yao, H.; Gadisa, A.; Zhang, H.; Li, S.; Ghasemi, M.; Balar, N.; Hunt, A.; O’Connor, B. T.; Hou, J.; Ade, H., High Performance Organic Solar Cells Processed by Blade Coating in Air from a Benign Food Additive Solution. Chem. Mater. 2016, 28 (20), 7451-7458.
 Ye, L.; Zhao, W.; Li, S.; Mukherjee, S.; Carpenter, J. H.; Awartani, O.; Jiao, X.; Hou, J.; Ade, H., High-Efficiency Nonfullerene Organic Solar Cells: Critical Factors that Affect Complex Multi-length Scale Morphology and Device Performance. Adv. Energy Mater. 2017, 7, 1602000.
 Ye, L.; Jiao, X.; Zhang, S.; Yao, H.; Qin, Y.; Ade, H.; Hou, J., Control of Mesoscale Morphology and Photovoltaic Performance in Diketopyrrolopyrrole-Based Small Band Gap Terpolymers. Adv. Energy Mater. 2017, 7, 1601138.
 Ye, L.; Jiao, X.; Zhao, W.; Zhang, S.; Yao, H.; Li, S.; Ade, H.; Hou, J., Manipulation of Domain Purity and Orientational Ordering in High Performance All-Polymer Solar Cells. Chem. Mater. 2016, 28 (17), 6178-6185.