Ni–Co/ZrO2 nanocomposite coatings were fabricated in a modified Watt’s bath by using high frequency pulse electrodeposition and the effects of pulse parameters such as frequency and duty cycle on the microstructure and properties were investigated. The surface morphology, phase structure, and microhardness of the Ni–Co/ZrO2 nanocomposite coatings were characterized by scanning electron microscopy with energy dispersive spectroscopy, X-ray diffraction and Vickers’ microhardness tester. The corrosion behaviour of the nanocomposites was evaluated by electrochemical impedance spectroscopy in the 3.5 wt% NaCl solution. The results revealed that increasing frequency and duty cycle resulted in a change of morphology from rough and porous structure to compact and homogeneous structure and reduced the ratio of relative intensity I(200)/I(111) of the Ni–Co/ZrO2 nanocomposites by intervening the adsorption–desorption of interfacial inhibitors at the cathode/solution interface. Furthermore, the effects of frequency and duty cycle on the microhardness of Ni–Co/ZrO2 nanocomposites should be associated with the ZrO2 nanoparticles according to dispersion strengthening from Orowan mechanism. It has been found that the corrosion resistance of the nanocomposites in 3.5 wt% NaCl solution depended on the incorporation of ZrO2 nanoparticles and the phase structure of Ni–Co/ZrO2 nanocomposites.

In this work, we present a new strategy to use fused and twisted conjugated backbones to construct conjugated small molecules and polymers as electron acceptors for non-fullerene solar cells. The new conjugated materials containing binary perylene bisimide (PBI) units linked with coplanar thieno[3,2-b]thiophene (as trans-PBI) or twisted thieno[2,3-b]thiophene (as cis-PBI) and the corresponding conjugated polymer cis-polyPBI were developed. A fused conjugated backbone ensures good charge transport, in which the twisted polymer cis-polyPBI was found to show the highest electron mobility of 1.2 × 10−2 cm2 V−1 s−1 in field-effect transistors. Meanwhile, a twisted conjugated backbone effectively prevents the aggregation and crystallization of PBI units, resulting in isotropic charge transport and finely tuned micro-phase separation in bulk-heterojunction thin films. The high electron mobility and isotropic crystallinity make the fused and twisted electron acceptors achieve high power conversion efficiencies above 6% in non-fullerene solar cells, while the coplanar molecule trans-PBI as the electron acceptor shows a very low efficiency of 0.13%.

In this work, we provide systematic studies on the non-fullerene solar cells based on diketopyrrolopyrrole (DPP) polymers as electron donors and a well-known electron acceptor ITIC. ITIC has been widely reported in non-fullerene solar cells with high power conversion efficiencies (PCEs) above 10%, when it is combined with a wide band gap conjugated polymer, while its application in small band gap DPP polymers has never been reported. Herein, we select four DPP polymers containing different thienyl linkers, resulting in distinct absorption spectra, energy levels and crystalline properties. Non-fullerene solar cells based on DPP polymers as donors and ITIC as an acceptor show PCEs of 1.9–4.1% and energy loss of 0.55–0.82 eV. The PCEs are much lower than those of cells based on fullerene derivatives due to the poor miscibility between the DPP polymers and ITIC, as confirmed by the morphology and charge transport investigation. The results indicate that it is important to tune the miscibility between the donor and acceptor in order to realize optimized micro-phase separation, which can further enhance the performance of DPP polymer based non-fullerene solar cells.

In this work, solution-processed organic solar cells with conjugated small molecules both as electron donors and electron acceptors were studied, where the influence of the chemical structures of the donor and acceptor on the device performance was systematically investigated. A small molecular donor incorporating binary electron-deficient units, diketopyrrolopyrrole and pentacyclic aromatic bislactam, was synthesized to provide a low band gap of 1.65 eV and low-lying energy levels. Three molecules, from a fullerene derivative to non-fullerene perylene bisimide-based acceptors, were selected as electron acceptors to construct organic solar cells. The results showed that fullerene-based solar cells provided power conversion efficiencies (PCEs) of up to 4.8%, while the non-fullerene solar cells also exhibited promising PCEs of 2.4% and 3.5%, with a photoresponse of up to 750 nm. Further analysis of the bulk-heterojunction systems between donors and acceptors revealed that the relatively low carrier mobilities of the non-fullerene acceptors and the large phase separations are mainly responsible for the less efficient solar cells. Our results demonstrate that molecules containing several electron-deficient units can effectively reduce the band gap of small molecules, and thus offer great potential for realizing high performance fullerene and non-fullerene solar cells.

In this work, we provide systematic studies on the non-fullerene solar cells based on diketopyrrolopyrrole (DPP) polymers as electron donors and a well-known electron acceptor ITIC. ITIC has been widely reported in non-fullerene solar cells with high power conversion efficiencies (PCEs) above 10%, when it is combined with a wide band gap conjugated polymer, while its application in small band gap DPP polymers has never been reported. Herein, we select four DPP polymers containing different thienyl linkers, resulting in distinct absorption spectra, energy levels and crystalline properties. Non-fullerene solar cells based on DPP polymers as donors and ITIC as an acceptor show PCEs of 1.9–4.1% and energy loss of 0.55–0.82 eV. The PCEs are much lower than those of cells based on fullerene derivatives due to the poor miscibility between the DPP polymers and ITIC, as confirmed by the morphology and charge transport investigation. The results indicate that it is important to tune the miscibility between the donor and acceptor in order to realize optimized micro-phase separation, which can further enhance the performance of DPP polymer based non-fullerene solar cells.

In this work, solution-processed organic solar cells with conjugated small molecules both as electron donors and electron acceptors were studied, where the influence of the chemical structures of the donor and acceptor on the device performance was systematically investigated. A small molecular donor incorporating binary electron-deficient units, diketopyrrolopyrrole and pentacyclic aromatic bislactam, was synthesized to provide a low band gap of 1.65 eV and low-lying energy levels. Three molecules, from a fullerene derivative to non-fullerene perylene bisimide-based acceptors, were selected as electron acceptors to construct organic solar cells. The results showed that fullerene-based solar cells provided power conversion efficiencies (PCEs) of up to 4.8%, while the non-fullerene solar cells also exhibited promising PCEs of 2.4% and 3.5%, with a photoresponse of up to 750 nm. Further analysis of the bulk-heterojunction systems between donors and acceptors revealed that the relatively low carrier mobilities of the non-fullerene acceptors and the large phase separations are mainly responsible for the less efficient solar cells. Our results demonstrate that molecules containing several electron-deficient units can effectively reduce the band gap of small molecules, and thus offer great potential for realizing high performance fullerene and non-fullerene solar cells.