A novel fluorinated copolymer (F-PCPDTBT) is introduced and shown to exhibit significantly higher power conversion efficiency in bulk heterojunction solar cells with PC(70)BM compared to the well-known low-band-gap polymer PCPDTBT. Fluorination lowers the polymer HOMO level, resulting in high open-circuit voltages well exceeding 0.7 V. Optical spectroscopy and morphological studies with energy-resolved transmission electron microscopy reveal that the fluorinated polymer aggregates more strongly in pristine and blended layers, with a smaller amount of additives needed to achieve optimum device performance. Time-delayed collection field and charge extraction by linearly increasing voltage are used to gain insight into the effect of fluorination on the field dependence of free charge-carrier generation and recombination. F-PCPDTBT is shown to exhibit a significantly weaker field dependence of free charge-carrier generation combined with an overall larger amount of free charges, meaning that geminate recombination is greatly reduced. Additionally, a 3-fold reduction in non-geminate recombination is measured compared to optimized PCPDTBT blends. As a consequence of reduced non-geminate recombination, the performance of optimized blends of fluorinated PCPDTBT with PC(70)BM is largely determined by the field dependence of free-carrier generation, and this field dependence is considerably weaker compared to that of blends comprising the non-fluorinated polymer. For these optimized blends, a short-circuit current of 14 mA/cm(2), an open-circuit voltage of 0.74 V, and a fill factor of 58% are achieved, giving a highest energy conversion efficiency of 6.16%. The superior device performance and the low band-gap render this new polymer highly promising for the construction of efficient polymer-based tandem solar cells.

We have applied time-delayed collection field (TDCF) and charge extraction by linearly increasing voltage (CELIV) to investigate the photogeneration, transport, and recombination of charge carriers in blends composed of PCPDTBT/PC70BM processed with and without the solvent additive diiodooctane. The results suggest that the solvent additive has severe impacts on the elementary processes involved in the photon to collected electron conversion in these blends. First, a pronounced field dependence of the free carrier generation is found for both blends, where the field dependence is stronger without the additive. Second, the fate of charge carriers in both blends can be described with a rather high bimolecular recombination coefficients, which increase with decreasing internal field. Third, the mobility is three to four times higher with the additive. Both blends show a negative field dependence of mobility, which we suggest to cause bias-dependent recombination coefficients.

New polymers with high electron mobilities have spurred research in organic solar cells using polymeric rather than fullerene acceptors due to their potential of increased diversity, stability, and scalability. However, all‐polymer solar cells have struggled to keep up with the steadily increasing power conversion efficiency of polymer:fullerene cells. The lack of knowledge about the dominant recombination process as well as the missing concluding picture on the role of the semi‐crystalline microstructure of conjugated polymers in the free charge carrier generation process impede a systematic optimization of all‐polymer solar cells. These issues are examined by combining structural and photo‐physical characterization on a series of poly(3‐hexylthiophene) (donor) and P(NDI2OD‐T2) (acceptor) blend devices. These experiments reveal that geminate recombination is the major loss channel for photo‐excited charge carriers. Advanced X‐ray and electron‐based studies reveal the effect of chloronaphthalene co‐solvent in reducing domain size, altering domain purity, and reorienting the acceptor polymer crystals to be coincident with those of the donor. This reorientation correlates well with the increased photocurrent from these devices. Thus, efficient split‐up of geminate pairs at polymer/polymer interfaces may necessitate correlated donor/acceptor crystal orientation, which represents an additional requirement compared to the isotropic fullerene acceptors.

Homoallyl amines were synthesized by visible-light irradiation of CdS powder in the presence of N-phenylbenzophenone imine and cyclohexene, 2,3-dihydrofuran, 2,5-dihydrofuran, 3,4-dihydropyran, 2-pentene, cyclopentene, 1 -methylcyclohexene, or a-pinene. The structures of the products from the last three olefins were determined by singlecrystal X-ray analysis to prove that C-alkylation of the imine had occurred. Thus, the reaction is formally an insertion of the imine into an allylic C-H bond of the olefin. It is proposed that a photogenerated electron-hole pair reduces the imine to an a-aminodiphenylmethyl radical and oxidizes the olefin with concomitant deprotonation to the corresponding allyl radical. Heterocoupling of these in-

Irradiation of methanolic cadmium sulfide suspensions in the Results and DiscussionAddition of Cyclopentene: Irradiation of a methanolic CdS suspension in the presence of the Schiff bases l a -l d and an excess of cyclopentene afforded the addition products 2a-2d and the hydrodimers 3a-3c (Scheme 1). HPLC analysis indicated a quantitative transformation of 1 a into Heterogeneous Photocatalysis, XIV. -Part XIII: 2a and 3a, the ratio of 2a to 3a being 6:l. After complete disappearance of the imine component the products were isolated in yields of 50-9576 by preparative HPLC. 3d was formed in very low concentrations and no attempts were made for its isolation.The structure of the y,6-unsaturated amines was deduced from their mass spectra and one-and two-dimensional 'Hand I3C-NMR analyses. Since the addition reaction generates two chral centers, a racemic mixture of four diastereomers was obtained. The two enantiomeric pairs could be identified in the 'H'H COSY and 'H13C COSY NMR spectrum as displayed for 2a in Figure 1.The signals of the methylene protons at C-6 and C-5 appear as a multiplet at 6 = 1.65-2.20 and 2.20-2.45, respectively. The protons at C-1 and C-2 give rise to two doublets of equal intensities at 6 = 4.15 (3J = 6.5 Hz) and 4.28 (3J = 4.5 Hz) as well as to two multiplets at 6 = 3.08 and 3.16, respectively. This and the four multiplets of the olefinic protons at C-3 (6 = 5.44, 5.52) and C-4 (6 = 5.88, 5.96) clearly indicate the presence of two diastereomers. The presence of a C-C bond between C-1 and the cyclopentenyl group at the allylic carbon atom C-2 is proved by the 'H'H COSY spectrum; the proton 1-H gives rise to an intensive cross peak with 2-H which further couples with 6-H. Whereas in the case of 2a coupling of 2-H with the olefinic proton 3-H could not be detected, this coupling was observed in the COSY spectra of the other addition products. The appearance of a set of two slightly shifted cross peak patterns is further evidence for the presence of a diastereomeric mixture (Figure 1).