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A cluster type of electron acceptor, TPB, bearing four α-perylenediimides (PDIs), was developed, in which the four PDIs form a cross-like molecular conformation while still partially conjugated with the BDT-Th core. The blend TPB:PTB7-Th films show favorable morphology and efficient charge dissociation. The inverted solar cells exhibited the highest PCE of 8.47% with the extraordinarily high Jsc values (>18 mA/cm(2)), comparable with those of the corresponding PC71BM/PTB7-Th-based solar cells.

1 www.MaterialsViews.com wileyonlinelibrary.com of the relationship between polymeric structure of the donor material and device performance. Among the factors that may infl uence solar energy conversion, the nature of electron donating and accepting materials and the morphology of the composites play the crucial roles in determining the fi nal performance of the devices. In recent years, fullerene derivatives such as [6,6]-phenyl C 71 -butyric acid methyl ester (PC 71 BM) have been widely adopted as electron acceptors due to their low lying energy levels and relatively high electron affi nity and mobility. It was also found that addition of a small amount of high boiling point solvent, generally 1,8-diiodooctane (DIO), can reliably improve the morphology of most of the composite systems. [ 19,20 ] Thus, we focus our main effort on understanding the structure/property correlation of electron donor materials in order to develop innovative strategies for achieving high performance solar cells.Numerous factors can infl uence the optical and electrical properties of low bandgap polymers. Our previous research indicated that the calculated internal dipole moment change between the ground and excited states of a polymer's repeating units, Δµ ge , showed a linear correlation with solar cell performance when other factors, such as morphology and charge carrier mobility, are comparable. [ 21,22 ] Crucial questions to be answered are that what will happen when Δµ ge is further increased, and why such a phenomenological model works well in a certain range. In this paper, calculations of dipolar change based on the polymer repeating units led us to identify two polymer systems, both copolymers containing benzodithiophene (BDT). One is based on thieno[3,4-c]pyrrole-4,6-dione (TPD) and the other on 3-oxothieno[3,4-d ]isothiazole 1,1-dioxide (TID). The TPD unit has recently been incorporated into various low band gap conjugated polymer systems. [23][24][25] Previously explored as an artifi cial sweetener, TID unit bears both a sulfonyl and a carbonyl group, and is more electron defi cient than TPD. The calculation results showed that the repeating units of both polymers containing TPD and TID (PPB and PID, respectively) exhibit a larger Δµ ge than our previous champion polymer PTB7. Thus, two polymers, PPB and PID, were synthesized and characterized Tao Tuning the Polarizability in Donor Polymers with a Thiophenesaccharin Unit for Organic Photovoltaic Applications

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We report the properties of a new series of wide band gap photovoltaic polymers based on the N-alkyl 2-pyridone dithiophene (PDT) unit.