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[3,4-g]thieno[3,2-c]-iso-quinoline-5,11-dione (TPTI), are synthesized and characterized. The comparative investigation of the photostabilities of the copolymers revealed that the PDTBDT-TPTI film exhibited the comparable photostability in relative to P3HT. Meanwhile, the inverted photovoltaic cells (i-PVCs) from the blend films of PBDT-TPTI and/or PDTBDT-TPTI with PC 71 BM, in which poly[(9,9-bis(3 0 -(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] were used as cathode modifying interlayer, presented higher power conversion efficiencies (PCEs) of 5.98% and 6.05% with photocurrent response ranging from 300 nm to 650 nm in contrast with the PCEs of 4.48% for the optimal inverted PVCs from P3HT/PC 71 BM under AM 1.5 G 100 mW/cm 2 . The PCEs of the i-PVCs from PBDT-TPTI and PDTBDT-TPTI were improved to 7.58% and 6.91% in contrast to that of 0.02% for the P3HT-based i-PVCs, and the photocurrent responses of the devices were extended to 300-792 nm, when the ITIC was used as electron acceptor materials. The results indicate that the PBDT-TPTI and PDTBDT-TPTI can be used as the promising alternatives of notable P3HT in the photovoltaic application. INTRODUCTION In last decades, the development of novel low band gap (LBG) donor conjugated polymers (CPs) has been demonstrated to be the most vigorous and promising approach to achieve high performance polymeric photovoltaic cells (PVCs), and various high performance LBG CPs have been presented. [1][2][3][4][5][6][7][8][9][10][11] Generally, the improvement of the short circuit current density (J sc ) can be achieved by narrowing the band gaps of the LBG CPs. Unfortunately, this approach usually compromised the trade-off problem such as the decrease of the open circuit voltage (V oc ) with the increase of the J sc of the PVCs from the LBG CPs. 12,13 To use solar radiation more effectively and achieve high performance

In recent years, ternary organic photovoltaic cells (OPVs) have been dedicated to improving power conversion efficiency (PCE) by broadening optical absorption spectra. Ternary OPVs with different poly[thieno[3,2-b]thiophene-2,5-diyl-alt-4,9-bis(4-(2-decyltetradecyl)thien-2-yl)naphtho[1,2-c:5,6-c’]bis[1,2,5]thiadiazole-5,5′-diyl] (PTT-DTNT-DT) doping concentrations were designed and the effect of PTT-DTNT-DT as a complementary electron donor on the performance of OPVs was investigated. The optimized PCE of OPVs was increased from 3.42% to 4.66% by doping 20 wt % PTT-DTNT-DT. The remarkable improvement in the performance of the ternary device is mainly attributed to the sharp increase in the short-circuit current density and fill-factor. The major reasons have been systematically studied from atomic force microscopy, electrochemical impedance spectroscopy, surface energy, space charge limited current and photocurrent behavior. It has been found that the separation of excitons and the transportation of charge are enhanced while light absorption is increased, and the charge recombination also decreases due to the optimization of the cascade energy level and the morphology of the ternary active layer. The results show that it is feasible to improve the performance of ternary OPVs by their complementary absorption.

Doping a low-bandgap polymer material (PDTBDT-DTNT) as a complementary electron donor in poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C 61 -butyricacid methyl ester (PC 61 BM) blend is experimented to improve the power conversion efficiency (PCE) of organic solar cells (OSCs).The PCE of OSCs was increased from 3.19% to 3.75% by doping 10 wt% PDTBDT-DTNT, which was 17.55% higher than that of the OSCs based on binary blend of P3HT:PC 61 BM (host cells).The short-circuit current density (J sc ) was increased to 10.11 mA·cm −2 compared with the host cells. Although the PCE improvement could partly be attributed to more photon harvest for complementary absorption of 2 donors by doping appropriate PDTBDT-DTNT, the promotion of charge separation and transport as well as the suppression of charge recombination due to a matrix of cascade energy levels is also important. And the better morphology of the active layer films is beneficial to the optimized performance of ternary devices.

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