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Environmentally benign solvent-processed photoactive materials are urgently required to replace the current toxic solvent processing, especially for nonfullerene organic solar cells (NFOSCs). In this regard, we report an efficient new π-conjugated polymer (P1) for high performance NFOSCs. The careful choice of side chain, number-average molecular weight (M n) tuning (low, medium, and high M n, denoted as P12, P19, and P32), and dedicated device engineering of NFOSCs resulted an impressive device performance. Interestingly, P19-based NFOSCs achieved a high power conversion efficiency (PCE) of over 10% with nonhalogenated solvents, which is much superior than the P12- and P32-based NFOSCs. The high performance of P1-M-M n polymer is very well correlated with its high short-circuit current density and fill factor values attained via well-defined active layer morphology. Moreover, the energy losses of the optimized devices are lower, which is very well correlated with the high V oc of the NFOSCs. Additionally, the ambient stability of the NFOSCS processed from nonhalogenated solvents is relatively higher than halogenated solvents because of the better morphological stability of nonhalogenated processed films. Overall, our study provides deep insight on M n impact on nonhalogenated processing and thereby efficiency enhancement in environmentally sustainable NFOSCs.

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The ternary-blend approach has the potential to enhance the power conversion efficiencies (PCEs) of polymer solar cells (PSCs) by providing complementary absorption and efficient charge generation. Unfortunately, most PSCs are processed with toxic halogenated solvents, which are harmful to human health and the environment. Herein, we report the addition of a nonfullerene electron acceptor 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3- d:2',3'- d']- s-indaceno[1,2- b:5,6- b']dithiophene (ITIC) to a binary blend (poly[4,8-bis(2-(4-(2-ethylhexyloxy)3-fluorophenyl)-5-thienyl)benzo[1,2- b:4,5- b']dithiophene- alt-1,3-bis(4-octylthien-2-yl)-5-(2-ethylhexyl)thieno[3,4- c]pyrrole-4,6-dione] (P1):[6,6]-phenyl-C-butyric acid methyl ester (PCBM), PCE = 8.07%) to produce an efficient nonhalogenated green solvent-processed ternary PSC system with a high PCE of 10.11%. The estimated wetting coefficient value (0.086) for the ternary blend suggests that ITIC could be located at the P1:PCBM interface, resulting in efficient charge generation and charge transport. In addition, the improved current density, sustained open-circuit voltage and PCE of the optimized ternary PSCs were highly correlated with their better external quantum efficiency response and flat-band potential value obtained from the Mott-Schottky analysis. In addition, the ternary PSCs also showed excellent ambient stability over 720 h. Therefore, our results demonstrate the combination of fullerene and nonfullerene acceptors in ternary blend as an efficient approach to improve the performance of eco-friendly solvent-processed PSCs with long-term stability.

We synthesized a new random π-conjugated polymer (asy-PBDTPBT) and investigated the effect of its structural irregularity. The efficiency of non-fullerene OSCs was enhanced, showing the suppressed crystallinity and the smaller domain size.