Recent years have seen a rapid progress in the power conversion efficiencies (PCEs) of non-fullerene polymer solar cells (NF PSCs). However, the donor materials accordingly used are typical low or medium band gap polymers, some of which possess badly overlapped absorption spectra relative to the low band gap n-type acceptors, for example, 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 obtain polymers simultaneously owning a wide band gap, a highly extended π-conjugation system, and a low-lying highest occupied molecular orbital (HOMO), a polymer (PBDTSi-TA) incorporating 2-(triisopropylsilylethynyl)thiophene substituted benzodithiophene (BDTSi) and fluorinated benzotriazole (FTAZ) units was designed and synthesized. PBDTSi-TA (Egopt = 1.92 eV) exhibits strong molecular aggregation properties and a lower-lying HOMO energy level compared to its structural analogues. When blended with ITIC and after device optimization with solvent vapor annealing in combination with a developed PDIN/BCP/Ag cathode structure, PSCs yielded a PCE of 7.51%, with Voc = 0.96 V. Moreover, a rather small energy loss (Eloss) of 0.6–0.63 eV was determined. For comparison, another polymer (PBDTSi-Qx) with a more-electron-deficient quinoxaline-based acceptor unit was also synthesized and applied to NF PSCs. Charge generation rate, exciton dissociation probabilities, dark leakage current, nanoscale morphology, and charge carrier mobilities have been evaluated to probe the reasons for the differentiated performances. The results suggest that PBDTSi-TA is a promising donor material for NF PSCs, and the molecular design strategy demonstrated here would be helpful for pursuing high-performance polymers for PSCs.Keywords: benzodithiophene; high open-circuit voltage; polymer solar cells; trialkylsilylethynyl; wide band gap polymers;

•Ternary organic solar cells based on PTB7-Th:DR3TBDTT:PC71BM activity system were prepared.•The higher energy conversion efficiency of 9.25% was achieved doping DR3TBDTT.•The doping of DR3TBDTT can improve the morphology of the device and the performance of the ternary organic solar cells.The recent stunning rise in power conversion efficiencies (PCEs) of ternary organic solar cells (OSCs) has triggered much attention. However, achieving high PCE values are quite challenging because the ternary system is complicated on phase separation behavior. In this work, ternary organic solar cells (OSCs) with one acceptor (PC71BM) and two donors, i.e., one polymer (PTB7-Th) and one small molecule (DR3TBDTT) have been fabricated. We substantially improved PCE from the best reported value of 7.53%–9.25% with increase of 22.8%, and an averaged PCE of 9.25% is obtained due to the improvement of the fill factor (FF) and the short-circuit current density (Jsc). The results of atomic force microscopy (AFM) indicate that a highly ordered molecular compatibility could be obtained by forming alloy with two miscible donors, and the doping of DR3TBDTT not only protects the long distance charge transport in the original binary system, but also improves the size of phase separation of the active layer within the ternary OSCs, thus forming the ordered nano morphology, which can improve the mobility of hole and reduce the charge recombination.

Organic solar cells (OSCs) have emerged as an attractive strategy to efficiently convert light energy into electricity. In this study, the third component 1-bromo-4-nitrobenzene (C6H4BrNO2) was introduced into the active layer of PTB7-Th:PC71BM to promote exciton separation and speed up electron transfer. A PCE of 8.95% was achieved for polymer solar cells (PSCs) with 15 wt% C6H4BrNO2, which is an 18% enhancement in PCE compared with binary OSCs based on PTB7-Th:PC71BM. Atomic force microscopy (AFM) measurements indicated that the ideal morphology can be formed. The charge generation properties were studied in terms of internal quantum efficiency (IQE) and photocurrent density (Jph), revealing that charge transport was facilitated significantly, which favors higher JSC and FF.

•1-Bromo-4-Nitrobenzene is first introduced to P3HT:PCBM active layer of PSCs.•Results show that it has a good inhibitory effect on the generation of fluorescence.•Electron transfer complexes (P3HT–C6H4BrNO2) is proved to be formed.•The PCE increase from 3.3% to 5.2%, which is an improvement of more than 57%.A fluorescent inhibitor, 1-Bromo-4-Nitrobenzene (1-Br-4-NB, C6H4BrNO2), is introduced to poly(3-hexylthiophene) (P3HT)/[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) active layer of polymer solar cells (PSCs). When the amount of 1-Br-4-NB added is 25 wt%, the device performance of PSCs is optimal. To investigate the means by which the power conversion efficiency (PCE) is improved, external quantum efficiency (EQE), fluorescence spectrum, transient absorption spectroscopy and dynamics photoresponse, X-ray diffraction (XRD) patterns are measured and density functional theory (DFT) calculations are carried out. The results indicate that excitonic recombination to the ground state is reduced and excitonic dissociation at the donor–acceptor interface is enhanced, which explains the inhibitory effect on the generation of fluorescence. Moreover, the electron transfer complexes (P3HT–C6H4BrNO2) is demonstrated to be formed after the addition of 1-Br-4-NB. The PCE of PSCs achieves an improvement of more than 57% compared to the reference solar cell without 1-Br-4-NB.1-Bromo-4-Nitrobenzene (1-Br-4-NB, C6H4BrNO2) is introduced to poly(3-hexylthiophene) (P3HT)/[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) active layer of polymer solar cells. Results show that 1-Br-4-NB and P3HT form stable coplanar charge transfer complexes through hydrogen bonds. Formation of the P3HT–C6H4BrNO2 complex leads to reduced excitonic recombination to the ground state through fluorescence emission and enhanced excitonic dissociation at the donor–acceptor interface. As a result, the PCE of the PSCs is improved due to the increased photoelectric conversion efficiency.

Organic polymer solar materials are shown to exhibit better solubility in mixed solvents than in pure ones, which affects the performance of their solar cells. In this article, poly[N-9-hepta-decanyl-2,7-carbazole-alt-5,5-(4,7-di-2-thienyl-2,1,3-benzothiadiazole) (PCDTBT) and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) are used as active layer materials in solar cells. To optimize the performance of these active materials, the ratio of chloroform (CF) to chlorobenzene used as solvents to dissolve PCDTBT, and PC71BM is varied, which is shown to affect power conversion efficiency (PCE). The solar cell that shows the best performance with a PCE as high as 6.82 % is produced using a volume ratio of CF to chlorobenzene of 1:1.

A method to improve the efficiency of organic photovoltaic cells through inclusion of an ultrathin modification layer of Al2O3 or LiF sandwiched between poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid (PEDOT:PSS) and indium tin oxide layers is developed. Because of the strong dipole moments of LiF and Al2O3, either can enhance the built-in electric field, which increases the probability of the carriers reaching the corresponding electrode. In addition, the low work function of PEDOT:PSS can decrease the energy barrier for carrier transmission. A 21.7% improvement in the power conversion efficiency of experimental devices was achieved, mainly because the short circuit current was enhanced by almost 30%.