Highly Bendable Flexible Perovskite Solar Cells on a Nanoscale Surface Oxide Layer of Titanium Metal Plates

We report highly bendable and efficient perovskite solar cells (PSCs) that use thermally oxidized layer of Ti metal plate as an electron transport layer (ETL). The power conversion efficiency (PCE) of flexible PSCs reaches 14.9% with a short-circuit current density (<i>J</i>_sc) of 17.9 mA/cm², open-circuit voltage (<i>V</i>_oc) of 1.09, and fill factor (ff) of 0.74. Moreover, the Ti metal-based PSCs exhibit a superior fatigue resistance over indium tin oxide/poly­(ethylene terephthalate) substrate. Flexible PSCs maintain 100% of their initial PCE even after PSCs are bent 1000 times at a bending radius of 4 mm. This excellent performance of flexible PSCs is due to high crystalline quality and low oxygen vacancy concentration of TiO₂ layer. The concentration of oxygen vacancies in the oxidized Ti metal surface controls the electric function of TiO₂ as ETL of PSCs. A decrease in the oxygen vacancy concentration of the TiO₂ layer is critical to improving the electron collection efficiency of the ETL. Our results suggest that Ti metal-based PSCs possess excellent mechanical properties, which can be applied to the renewable energy source for flexible electronics

Depleted Bulk Heterojunctions in Thermally Annealed PbS Quantum Dot Solar Cells

We have studied the detailed interface structure and energy conversion behavior of TiO₂/PbS heterojunction solar cells. Nanoscale structure and composition analysis have revealed that thermal annealing causes intermixing of the TiO₂ and PbS phases and influences the morphologies and optical properties of the heterojunction film. This intermixing increased the junction area within the depleted bulk heterojunction (DBH) layer and promoted the carrier extraction from PbS QDs to TiO₂. In addition, the thermal annealing caused interparticle necking between PbS QDs and increased the crystallinity of the PbS QD film. Compared with unannealed PbS/TiO₂ heterojunction solar cells, the formation of the DBH layer and the partial sintering of PbS QDs led to a doubling of the short-circuit current (<i>J</i>_sc) and an improved energy conversion efficiency, by 39%. Electric force microscopy analysis confirmed the presence of a DBH layer. The electron lifetime and fill factor (FF) of the solar cells decreased when the TiO₂/PbS mixed film was thermally annealed, and this was assigned to a lower recombination resistance in the DBH layer. Post-treatment of PbS/TiO₂ DBH films with ethanedithiol was found to increase the recombination resistance at PbS/TiO₂ interface and to enhance the energy conversion efficiency to ∼4%

Additional file 1: Figure S1. of Room Temperature Deposition of Crystalline Nanoporous ZnO Nanostructures for Direct Use as Flexible DSSC Photoanode

J–V curves for four different ZnO electrodes with different dye and solution combination in 2 h sensitizing time. Figure S2. (a) J–V curves of DSSCs fabricated with nanostructured ZnO photoanodes as a function of dye adsorption time at 50 °C (all films were deposited under 300 mTorr and the thicknesses of all films were fixed to be 6.7 μm) and (b) as function of sample aging after fabrication. Table S1. Device parameters of dye-sensitized ZnO nanostructured photoanodes under simulated AM 1.5 G light illumination (a) as a function of dye adsorption time at 50 °C (the thicknesses of the films were fixed to be 6.7 μm) and (b) as function of sample aging after fabrication. Table S2. Dye loading of DSSCs fabricated with nanostructured ZnO photoanodes deposited under different ambient oxygen pressures. The thickness of the photoanodes was fixed to be 10 μm. Table S3. Statistical analysis of device parameters for five different DSSCs fabricated with nanostructured ZnO photoanodes deposited by PLD using the optimized condition. Figure S3. J–V curves of five different DSSCs fabricated with nanostructured ZnO photoanodes deposited by PLD using the optimized condition. Figure S4. The incident photon-to-current conversion efficiency (IPCE) spectrum of a DSSC with a nanostructured ZnO photoanode deposited under 300 mTorr by PLD. Figure S5. J–V curves of 300 mTorr 5-μm ZnO photoanodes deposited by PLD using PLD coupled with Pt/ITO/PEN flexible substrate. (DOCX 226 kb

Novel Carrier Doping Mechanism for Transparent Conductor: Electron Donation from Embedded Ag Nanoparticles to the Oxide Matrix

A trade-off between the carrier concentration and carrier mobility is an inherent problem of traditional transparent conducting oxide (TCO) films. In this study, we demonstrate that the electron concentration of TCO films can be increased without deteriorating the carrier mobility by embedding Ag nanoparticles (NPs) into Al-doped ZnO (AZO) films. An increment of Ag NP content up to 0.7 vol % in the AZO causes the electron concentration rising to 4 × 10²⁰ cm^–3. A dependence of the conductivity on temperature suggests that the energy barrier for the electron donation from Ag NPs at room temperature is similar to the Schottky barrier height at the Ag–AZO interface. In spite of an increase in the electron concentration, embedded Ag NPs do not compromise the carrier mobility at room temperature. This is evidence showing that this electron donation mechanism by Ag NPs is different from impurity doping, which produces both electrons and ionized scattering centers. Instead, an increase in the Fermi energy level of the AZO matrix partially neutralizes Al impurities, and the carrier mobility of Ag NP embedded AZO film is slightly increased. The optical transmittance of mixture films with resistivity less than 1 × 10^–3 Ω·cm still maintains above 85% in visible wavelengths. This opens a new paradigm to the design of alternative TCO composite materials which circumvent an inherent problem of the impurity doping

Indium–Tin–Oxide Nanowire Array Based CdSe/CdS/TiO₂ One-Dimensional Heterojunction Photoelectrode for Enhanced Solar Hydrogen Production

For photoelectrochemical (PEC) hydrogen production, low charge transport efficiency of a photoelectrode is one of the key factors that largely limit PEC performance enhancement. Here, we report a tin-doped indium oxide (In₂O₃:Sn, ITO) nanowire array (NWs) based CdSe/CdS/TiO₂ multishelled heterojunction photoelectrode. This multishelled one-dimensional (1D) heterojunction photoelectrode shows superior charge transport efficiency due to the negligible carrier recombination in ITO NWs, leading to a greatly improved photocurrent density (∼16.2 mA/cm² at 1.0 V vs RHE). The ITO NWs with an average thickness of ∼12 μm are first grown on commercial ITO/glass substrate by a vapor–liquid–solid method. Subsequently, the TiO₂ and CdSe/CdS shell layers are deposited by an atomic layer deposition (ALD) and a chemical bath deposition method, respectively. The resultant CdSe/CdS/TiO₂/ITO NWs photoelectrode, compared to a planar structure with the same configuration, shows improved light absorption and much faster charge transport properties. More importantly, even though the CdSe/CdS/TiO₂/ITO NWs photoelectrode has lower CdSe/CdS loading (i.e., due to its lower surface area) than the mesoporous TiO₂ nanoparticle based photoelectrode, it shows 2.4 times higher saturation photocurrent density, which is attributed to the superior charge transport and better light absorption by the 1D ITO NWs

Reduced Graphene Oxide/Mesoporous TiO₂ Nanocomposite Based Perovskite Solar Cells

We report on reduced graphene oxide (rGO)/mesoporous (mp)-TiO₂ nanocomposite based mesostructured perovskite solar cells that show an improved electron transport property owing to the reduced interfacial resistance. The amount of rGO added to the TiO₂ nanoparticles electron transport layer was optimized, and their impacts on film resistivity, electron diffusion, recombination time, and photovoltaic performance were investigated. The rGO/mp-TiO₂ nanocomposite film reduces interfacial resistance when compared to the mp-TiO₂ film, and hence, it improves charge collection efficiency. This effect significantly increases the short circuit current density and open circuit voltage. The rGO/mp-TiO₂ nanocomposite film with an optimal rGO content of 0.4 vol % shows 18% higher photon conversion efficiency compared with the TiO₂ nanoparticles based perovskite solar cells