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Inverted organic solar cells (OSCs) have been fabricated with conventional Sn-doped indium oxide (ITO) and amorphous indium gallium zinc oxide (a-IGZO)/Ag/a-IGZO (39 nm/19 nm/39 nm) (a-IAI) electrodes and their electrical characteristics characterized. The ITO and optimized a-IAI electrodes showed high transmittance of 96% and 88% at 500 nm, respectively. The carrier concentration and sheet resistance of the ITO and a-IAI films were 8.46 × 10 cm and 7.96 × 10 cm and 14.18 Ω/sq and 4.24 Ω/sq, respectively. Electron transport layer (ETL)-free OSCs with the a-IAI electrode exhibited power conversion efficiency (PCE) of 2.66%, similar to that of ZnO ETL-based OSCs with ITO electrode (3.27%). However, the ETL-free OSCs with the a-IAI electrode showed much higher PCE than the ETL-free OSCs with the ITO electrode (0.84%). Ultraviolet photoelectron spectroscopy results showed that the work function of the a-IAI electrode was 4.15 eV. This improved performance was attributed to the various roles of the a-IAI electrode, e.g., as an effective ETL and a hole blocking layer. [ABSTRACT FROM AUTHOR]

Efficient inverted polymer solar cells (PSCs) were fabricated with ZnO electron transport layers (ETLs) prepared by spray pyrolysis, which is a simple and cost efficient method producing a thin oxide layer by direct spray of precursor on hot substrate. To investigate the effect of substrate temperature on the structural and optical properties as well as performance of PSCs, ZnO ETLs were fabricated by spray pyrolysis on hot substrate controlled at 150, 250, and 350°C, respectively. The PSC with ZnO prepared by spray pyrolysis at 150°C exhibited poor power conversion efficiency (PCE) of 0.94% due to the mis-matched energy level and microscopic roughness of ZnO ETL. On the other hand, enhanced efficiency of 2.99% and 3.22% was obtained by using ZnO prepared by spray pyrolysis at 250 and 350°C, respectively. Enhancement of efficiency at higher temperature is attributed to better matching of ZnO coated ITO work-function with the lowest unoccupied molecular orbital (LUMO) energy level of PCBM and the formation of smooth and homogeneous polycrystalline ZnO, resulting in improved interfacial property and electron transport. In the durability test, inverted ZnO solar cell was retained above 80% during 9 days in an ambient atmosphere without any encapsulation, while conventional solar cells showed dramatic decrease of efficiency. [ABSTRACT FROM AUTHOR]

The authors report the characteristics of organic solar cells (OSCs) fabricated on HNO3-treated multilayer graphene (MLG) transparent electrodes. MLG transparent electrodes were prepared using chemical vapor deposition and a multitransfer process. Compared to untreated-MLG electrodes with a fairly high sheet resistance (274 ± 1 Ω/sq) even though three layers of graphene were stacked together, HNO3-treated MLG electrode shows a lower sheet resistance of 119 ± 1 Ω/sq. OSCs (MLG/poly (3,4-ethylenedioxythiophene):poly(styrenesulfonate)/Poly(3-hexylthiophere)/1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61/Ca/Al) fabricated on untreated-MLG transparent electrodes had an open-circuit voltage of 0.575 V, a short-circuit current of 8.08 mA/cm2, a fill factor of 43.5%, and a power conversion efficiency (PCE) of 2.02%. In contrast, application of HNO3-treated MLG films as transparent electrodes for OSCs led to improved performance with an open-circuit voltage of 0.602 V, a short-circuit current of 8.26 mA/cm2, a fill factor of 57.5%, and a PCE of 2.86%. These results suggest that HNO3 treatment is a promising method for improving the performance of large-area OSCs based on MLG electrodes. [ABSTRACT FROM AUTHOR]

Abstract: To increase the efficiency of TiO2 nanotube-based dye-sensitized solar cells, we fabricated TiO2 nanotubes and decorated them with ZnO rod-like nanostructures via anodization of Ti metal sheets followed by the hydrothermal growth of ZnO. Compared to conventionally anodized nanotubes, the modified nanotubes provided a higher specific surface area for dye adsorption. Besides increased dye adsorption, suppression of the recombination of photo-induced electrons at the electrode/electrolyte interface was observed in the modified nanotube-based systems because of the existence of a ZnO thin layer on the surface of nanotubes. This thin layer was applied as a seed for an oriented growth of ZnO. Dye-sensitized solar cells based on TiO2 nanotubes decorated with ZnO rod-like nanostructures showed a higher power conversion efficiency of 3.84%, compared to standard nanotube devices with an efficiency of 2.06%. [Copyright &y& Elsevier]

Abstract: We report on cost-effective ITO-free organic solar cells (OSCs) fabricated by a spray deposition method. All solution-processable layers of solar cells—a highly conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) layer and a photoactive layer based on poly(3-hexylthiophene) (P3HT) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 (PCBM)—were spray-coated. PEDOT:PSS anode films with various thicknesses were prepared by controlling the spray deposition time. The transmittance and sheet resistance of PEDOT:PSS anodes were varied from 89.0% to 67.4% and from 358 to 63.3Ω/squares, respectively, corresponding to an increase in film thickness. The best device exhibited a high power conversion efficiency of 2.17% under 100mWcm−2 illumination with air mass (AM) 1. 5 global (G) condition. More importantly, the efficiency of the fully spray-coated OSC with the PEDOT:PSS anode was comparable to that of conventional ITO-based devices, demonstrating the feasibility of fabricating all-spray-deposited OSCs without a conventional spin-coating method and the possibility of replacing the costly vacuum-deposited indium tin oxide (ITO) with highly conductive polymer films fabricated by inexpensive spray deposition techniques. [Copyright &y& Elsevier]

Abstract: We report on the fabrication of efficient annealing-free polymer solar cells via simple brush painting considered as a promising method for the mass production of organic devices based on the high-speed roll-to-roll system. Higher device efficiency could be obtained compared to the spin-coated devices, resulting from the improved organization of polymer chains and better balanced carrier transport induced by more effective application of shear stress to the polymer chains during the brushing process. In addition, fully brush painted solar cells, including the brush-painted PEDOT:PSS and photoactive layer, presented a high power conversion efficiency of 3.6% without any annealing treatment and processing additives. [Copyright &y& Elsevier]

We demonstrate the fabrication of inverted-structure organic solar cells (OSCs) with graphene cathodes. The graphene film used in this work was work-function-engineered with an interfacial dipole layer to reduce the work function of graphene, which resulted in an increase in the built-in potential and enhancement of the charge extraction, thereby enhancing the overall device performance. Our demonstration of inverted-structure OSCs with work-function-engineering of graphene electrodes will foster the fabrication of more advanced structure OSCs with higher efficiency. [ABSTRACT FROM AUTHOR]

Flexible organic solar cells (OSCs) composed of blended films of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) were fabricated and investigated with chemically doped multilayer graphene films as transparent and conducting electrodes on plastic substrates. The sheet resistance of the chemically doped graphene film was reduced to half of its original value, resulting in a significant performance enhancement of OSCs featuring doped graphene electrodes. Moreover, there was no substantial variation observed in the fill factor and power conversion efficiency values of the flexible OSCs under bending conditions. A power conversion efficiency of ∼2.5% for flexible OSCs with doped graphene electrodes was observed under bending conditions, even up to a 5.2 mm bending radius. [ABSTRACT FROM AUTHOR]

We introduce efficient planar heterojunction CH 3 NH 3 PbI 3 perovskite solar cells (PSCs) fabricated with a roller coating process under ambient conditions. The perovskite films were prepared with a roller coating of lead iodide (PbI 2 ) and a spin coating of methylammonium iodide (MAI), a successive roller coating of PbI 2 and MAI, and a spin coating of PbI 2 and MAI as a reference film. The PSCs with roller-coated perovskite films were systemically compared to a reference PSC with spin-coated PbI 2 and MAI. In order to investigate the effect of roller coating on PSC performance, scanning electron microscopy (SEM), UV–vis absorption, and X-ray diffraction (XRD) measurements were performed. With the PbI 2 roller coating, the PSCs showed excellent power conversion efficiencies (PCEs) of up to 9.52% under a standard 1-sun condition, quite comparable to the spin-coated PSCs. In addition, the PSCs with the all roller-coated PbI 2 and MAI showed high PCEs of up to 6.421%, and with the aid of an additive the PCEs were further enhanced of up to 7.356%. These results support the conclusion that roller coating can be used for the facile and cost-effective manufacture of high-efficiency solution-based PSCs. [ABSTRACT FROM AUTHOR]

Abstract: We demonstrate cost-effective, indium tin oxide (ITO)-free organic solar cells (OSCs) fabricated with a silver nanowire (AgNW)–poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) composite electrode. The composite films were prepared with a one-step spray-coating of a mixture composed of AgNW and a highly conductive, dimethylsulfoxide (DMSO)-treated PEDOT:PSS (hcPEDOT). The film-thickness, optical transmittance, and sheet resistance of AgNW–hcPEDOT hybrid electrodes were easily controlled by varying the spray deposition time. With AgNW–hcPEDOT composite electrodes, the devices exhibited high power conversion efficiencies of up to 2.16% under 100mWcm−2 and AM 1.5G illumination conditions. In addition, the surface of the AgNW–hcPEDOT composite electrodes was further smoothened with an additional spray-coated PEDOT:PSS buffer layer, leading to reduced shorting and improved cell-efficiency. As a result, the best performing devices with a AgNW–hcPEDOT electrode and spray-coated PEDOT buffer exhibited efficiencies of up to 2.65%, which approaches that of conventional ITO-based devices. These results indicate that the one-step spray-coated AgNW–hcPEDOT composite-based film is a viable alternative to the high-cost and vacuum-deposited ITO for mass-production and low-cost roll-to-roll based solar cells. [Copyright &y& Elsevier]

Abstract: We investigated flexible Ag nanowire (NW) network electrodes fabricated by simple brush-painting for cost-efficient FOSCs. By direct brush-painting Ag NWs on a PET substrate, we achieved Ag NW network electrodes with a low sheet resistance of 38.7Ω/square and a high diffusive transmittance of 87.62% as well as superior mechanical flexibility. The electrical, optical, and mechanical properties of the brush-painted Ag NW electrodes were investigated as a function of the number of repeated brush-painting cycles. Identical performances of the FOSC with the brush painted Ag NW network electrode to those of the FOSC with a conventional ITO electrode demonstrate that the brush-painted Ag NW electrode is a promising alternative to ITO films for cost-efficient FOSCs. Furthermore, simple brush-painting is a low-cost and simple coating process to fabricate solution-based simple transparent electrodes. [Copyright &y& Elsevier]

Abstract: As an alternative to the poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) hole transporting layer (HTL) in polymer solar cells (PSCs), moderately reduced graphene oxide (GO) films fabricated by simple and fast thermal treatment of solution processed GO were investigated. PSC with thermally treated GO at 250°C exhibited best performance with a power conversion efficiency (PCE) of 3.98%, compared to the PSC containing conventional PEDOT:PSS HTL with a PCE of 3.85%. Furthermore, the PSC with thermally treated GO showed superior stability compared to the PSC with conventional PEDOT:PSS HTL under the atmosphere condition without any encapsulation process. Our demonstration suggests that moderately reduced GO by simple thermal treatment could be promising HTL replacing PEDOT:PSS in PSCs as well as other organic electronics. [Copyright &y& Elsevier]

Abstract: Highly efficient and cost-effective polymer solar cells (PSCs) based poly(3-hexylthiophene) (P3HT) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 (PCBM) have been fabricated by inkjet-printing with various additives. All solution-processed layers in the solar cells—a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) layer and a photoactive layer based on P3HT and PCBM with additives—were inkjet-printed. The device performance is strongly influenced by the addition of high boiling point additives in the photoactive ink with chlorobenzene (CB) solvent. The morphology, optoelectronic properties, and overall solar cell performance of the devices were dramatically affected by additives, such as 1,8 octanedithiol (ODT), o-dichlorobenzene (ODCB) and chloronaphthalene (Cl-naph). A device fabricated from ink formulated with ODT exhibited the best overall performance with power conversion efficiency (PCE) of 3.71%. [Copyright &y& Elsevier]