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Fullerene‐based materials are widely used as electron acceptors in organic bulk‐heterojunction solar cells; yet, they have rarely been used as the only photoactive component due to their low absorbance and limited charge generation efficiency. However, blending the wide‐bandgap p‐type material copper (I) thiocyanate (CuSCN) with [6,6]‐phenyl‐C71‐butyric acid methyl ester (PC70BM) leads to the formation of a unique mesostructured p‐n like heterointerface between CuSCN and PC70BM and solar cells with a power conversion efficiency (PCE) of up to 5.4%. Here, we examine in detail the reasons for the surprisingly good device performance and elucidate the charge photogeneration and recombination mechanisms in CuSCN‐based devices with PC70BM as the exclusive light‐absorbing material. Our studies clearly demonstrate that a substantial fraction of the photocurrent in the CuSCN‐based devices results from improved dissociation of fullerene excitons and efficient charge transfer at the CuSCN:PC70BM interface combined with reduced geminate and nongeminate charge recombination losses. Our results have implications beyond the fullerene‐based devices studied here, as they demonstrate that careful selection of a mesostructured p‐type transparent semiconductor paves the path to a new type of efficient single photoactive material solar cells. [ABSTRACT FROM AUTHOR]

We calculate the combined angular-distribution functions of the polarized photons ( $$\gamma _1$$ and $$\gamma _2$$ ) and electron ( $$e^-$$ ) produced in the cascade process $$\bar{p}p\rightarrow {^3{D_3}}\rightarrow {^3{P_2}}+\gamma _1 \rightarrow (\psi +\gamma _2)+\gamma _1\rightarrow (e^++e^-)+\gamma _1+\gamma _2$$ , when the colliding $$\bar{p}$$ and $$p$$ are unpolarized. Our results are independent of any dynamical models and are expressed in terms of the spherical harmonics whose coefficients are functions of the angular-momentum helicity amplitudes of the individual processes. Once the joint angular distribution of ( $$\gamma _1$$ , $$\gamma _2$$ ) and that of ( $$\gamma _2$$ , $$e^-$$ ) with the polarization of either one of the two particles are measured, our results will enable one to determine the relative magnitudes as well as the relative phases of all the angular-momentum helicity amplitudes in the radiative decay processes $${^3{D_3}}\rightarrow {^3{P_2}}+\gamma _1$$ and $${^3{P_2}}\rightarrow \psi +\gamma _2$$ . [ABSTRACT FROM AUTHOR]

The vast majority of conjugated‐polymer‐based light emitting field‐effect transistors (LEFETs) are characterized by low charge‐carrier mobilities typically in the 10−5 to 10−3 cm2 V−1 s−1 range. Fast carrier transport is a highly desirable characteristic for high‐frequency LEFET operation and, potentially, for use in electrically pumped lasers. Unfortunately, high‐mobility organic semiconductors are often characterized by strong intermolecular π–π interactions that reduce luminescence. Development of new materials and/or device concepts that overcome this hurdle are therefore required. Single organic semiconductor layer based LEFETs that combine high hole mobilities with encouraging light emission characteristics are reported. This is achieved in a single polymer layer LEFET, which is further enhanced through the use of a small‐molecule/conjugated polymer blend system that possesses a film microstructure which supports enhanced charge‐carrier mobility (3.2 cm2 V−1 s−1) and promising light‐emission characteristics (1600 cd m−2) as compared to polymer‐only based LEFETs. This simple approach represents an attractive strategy to further advance the performance of solution‐processed LEFETs. [ABSTRACT FROM AUTHOR]

Organic solar cells that use only fullerenes as the photoactive material exhibit poor exciton‐to‐charge conversion efficiencies, resulting in low internal quantum efficiencies (IQE). However, the IQE can be greatly improved, when copper(I) thiocyanate (CuSCN) is used as a carrier‐selective interlayer between the phenyl‐C70‐butyric acid methyl ester (PC70BM) layer and the anode. Efficiencies of ≈5.4% have recently been reported for optimized CuSCN:PC70BM (1:3)‐mesostructured heterojunctions, yet the reasons causing the efficiency boost remain unclear. Here, transient absorption (TA) spectroscopy is used to demonstrate that CuSCN does not only act as a carrier‐selective electrode layer, but also facilitates fullerene exciton dissociation and hole transfer at the interface with PC70BM. While intrinsic charge generation in neat PC70BM films proceeds with low yield, hybrid films exhibit much improved exciton dissociation due to the presence of abundant interfaces. Triplet generation with a rate proportional to the product of singlet and charge concentrations is observed in neat PC70BM films, implying a charge–singlet spin exchange mechanism, while in hybrid films, this mechanism is absent and triplet formation is a consequence of nongeminate recombination of free charges. At low carrier concentrations, the fraction of charges outweighs the population of triplets, leading to respectable device efficiencies under one sun illumination. Charge and triplet exciton dynamics in neat fullerene and hybrid solar cells with fullerene as the only light absorber are investigated by transient spectroscopy. The efficiency and mechanism of charge generation and triplet formation depend on the photoactive layer composition. Formation of a hybrid bulk heterojunction leads to ultrafast exciton dissociation, fast charge extraction, and power conversion efficiencies in excess of 5%. [ABSTRACT FROM AUTHOR]