TiO2/CH3NH3PbI3 heterojunction solar cells were fabricated by spin-coating and characterized by current–voltage measurements, impedance spectroscopy and capacitance–voltage measurements. It was demonstrated that the TiO2/CH3NH3PbI3 layers form an ideal p–n heterojunction suitable for the photovoltaic applications. The active acceptor concentration of 9.67 × 1015 cm−3 in the CH3NH3PbI3 layer and the built-in potential of 0.67 eV in the TiO2/CH3NH3PbI3 heterojunction were derived by the Mott–Schottky relationship. Numerical simulations showed that the acceptor concentration in the CH3NH3PbI3 layer greatly influenced the electron potential barrier height at the junction interface. The degradation of TiO2/CH3NH3PbI3 heterojunction solar cells showed that the efficiency remained 35.5% after storage under ambient laboratory conditions for 15 days. These results indicated that the oriented TiO2 layers provide a possible route to fabricate stable perovskite-based photovoltaic devices without hole transporting materials.

•Inverted P3HT:PCBM organic solar cells based on TiOx/rGO composite as electron collecting layer were fabricated.•Voc and PCE of the device based on TiOx/rGO were enhanced, compared with the device based on TiOx.•Impedance spectra revealed that the electron collecting efficiency in TiOx/rGO composite was improved significantly.Graphene oxide (GO) was synthesized, and converted to reduced graphene oxide (rGO) during the preparation of electron collecting layers (TiOx) on ITO substrates in inverted P3HT:PCBM organic solar cells. The solar cells based on TiOx/rGO exhibited an open-circuit voltage and a power conversion efficiency of 0.659 V and 2.70%, enhanced by ∼6.8% and ∼8%, respectively, as compared with the devices based on TiOx. Impedance spectra revealed that the devices based on TiOx/rGO composite have a smaller charge transport time constant than of devices based on TiOx. The electron collecting efficiency was improved significantly, resulting in high open circuit voltage. Moreover, the stability properties of the cells based on TiOx/rGO showed that energy conversion efficiency decreased 27% of the first day value after 90 days under ambient conditions.

Reduced graphene oxide (RGO)/titanium oxide (TiOx) (RGO/TiOx) composite films are successfully prepared by a sol-gel method. Inverted organic solar cells incorporating RGO/TiOx composite as electron transport layer and MoO3 as hole transport layer were fabricated. A short-circuit current of 9.85 mA/cm2 and power conversion efficiency of 3.82% are achieved by using the RGO/TiOx composite films with 0.083 mg/mL of RGO in TiO2 colloidal solution as electron transport layers for the inverted solar cells based on P3HT and PCBM, which are increased by 14.8% and 26.1% compared with the reference device without RGO, respectively. Impedance measurements revealed that the significantly enhanced efficiency was attributed to the RGO/TiOx composite films with efficient electron transport.

The pristine TiOx and Zn-doped TiOx films with the different Zn/Ti doping ratios were prepared by a sol-gel method on ITO substrates, and used as electron transfer layers in inverted organic solar cells based on P3HT:PCBM. The highest electron mobility was achieved in the film with a Zn/Ti atomic ratio of 0.8%. The photovoltaic device based on the 0.8% Zn-doped TiOx film had a power conversion efficiency of 3.39%, increased by ∼35%, compared with 2.51% of the reference device based on the pristine TiOx film. The electrochemical impedance analysis revealed that the optimal device based on the 0.8% Zn-doped TiOx had the smallest charge transport resistance and the smallest charge transport time constant in all devices. The fast electron transport on the interface between the organic active layer and ITO cathode increased the open circuit voltage and short-circuit current density of inverted organic solar cells.

Organic P3HT:PCBM heterojunction solar cells with indium tin oxide (ITO) anodes modified by platinum nanoparticles (NPs) were fabricated. The open-circuit voltage (Voc) of the cells was increased compared with the reference cell without Pt NPs. An enhanced power conversion efficiency of ∼12% was obtained for the optimum sputtering deposition duration of 10 s. A double junction model of the Schottky junction and the p–n junction is proposed to describe the frequency dependence of the capacitance in the modified cell. The formation of the front Schottky junction allows efficient collection of holes from the active layer, and enhances the Voc. Moreover, the air stability of organic solar cells was improved. The modification of ITO with Pt NPs shows promise as a technique for fabrication of high-efficiency stable photovoltaic devices.Highlights► ITO anodes in P3HT:PCBM heterojunction solar cells were modified by Pt nanoparticles (NPs). ► The Voc and PCE of the cells were increased compared with the reference cell without Pt NPs. ► A double junction model of the Schottky junction and the p–n junction is proposed to describe the frequency dependence of the capacitance in the modified cells.

•Organic photovoltaic cells based on P3HT:PCBM were fabricated with different drying durations of 0, 30, 60, and 80 min before annealing.•The power conversion efficiency of the device with optimal 60 min drying increased by 10.3% compared with the device without drying.•AC impedance analysis indicated that the optimal drying duration of P3HT:PCBM blend film facilitated the formation of the electrically perfect interface between P3HT and PCBM.Organic photovoltaic cells based on P3HT:PCBM bulk heterojunctions were fabricated with different drying durations of 0, 30, 60, and 80 min before annealing. The 60 min drying of the active layer was optimal to form perfect P3HT crystals, and to achieve the power conversion efficiency of 3.97%, increased by 10.3% compared with the device without drying. AC impedance analysis indicated the 60 min drying of the active layer formed the electrically perfect interface between P3HT and PCBM for efficient charge transport and dissociation of excitons.

The electrical transport through nanoscale contacts of ZnO nanowires bridging the interdigitated Au electrodes shows the negative differential resistance (NDR) effect. The NDR peaks strongly depend on the starting sweep voltage. The origin of NDR through nanoscale contacts between ZnO nanowires and metal electrodes is the electron charging and discharging of the parasitic capacitor due to the weak contact, rather than the conventional resonant tunneling mechanism.

ZnO nanorod arrays with different structures were grown on Si substrates at different temperatures by using a chemical vapor transport process. The growth sites and population of ZnO nanorods were controlled by the primarily grown micropyramids. The density and size of these nanorods were greatly affected by the growth temperature. A growth mechanism is proposed which attributes the overgrowth of ZnO nanorods to the orientation adhesion and to the difference in the saturation pressure at different temperatures. The field emission (FE) measurements show that the high density arrays of small nanorods exhibit excellent FE properties.

ZnO:Zn hollow microspheres were fabricated on Si(1 0 0) substrates by a direct thermal oxidation process. The formation of ZnO spheres and hollow structures was due to liquid Zn droplets and the high evaporation temperature, respectively. Room temperature photoluminescence showed an ultraviolet band and a broad blue–green–yellow band. White-light emission was clearly observed due to mixtures of complementary colors, e.g. blue–yellow and violet–green. These ZnO:Zn hollow microspheres can therefore be used as white-light emitting materials.

TiO2/CH3NH3PbI3 heterojunction solar cells were fabricated by spin-coating and characterized by current–voltage measurements, impedance spectroscopy and capacitance–voltage measurements. It was demonstrated that the TiO2/CH3NH3PbI3 layers form an ideal p–n heterojunction suitable for the photovoltaic applications. The active acceptor concentration of 9.67 × 1015 cm−3 in the CH3NH3PbI3 layer and the built-in potential of 0.67 eV in the TiO2/CH3NH3PbI3 heterojunction were derived by the Mott–Schottky relationship. Numerical simulations showed that the acceptor concentration in the CH3NH3PbI3 layer greatly influenced the electron potential barrier height at the junction interface. The degradation of TiO2/CH3NH3PbI3 heterojunction solar cells showed that the efficiency remained 35.5% after storage under ambient laboratory conditions for 15 days. These results indicated that the oriented TiO2 layers provide a possible route to fabricate stable perovskite-based photovoltaic devices without hole transporting materials.