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In parallel with soaring efficiency, interest in multi-functional semitransparent perovskite solar cells (PeSCs) has emerged for special applications such as windows and tandem cells. To demonstrate air-stable as well as efficient ITO-free semitransparent PeSCs, ultra thin Cu and Ni, which are well-known non-precious metals having sufficient electrical conductivity, are investigated as bottom transparent electrode and optimization of devices is systematically carried out. Semitransparent Ni/NiOX based PeSC exhibits the average visible transmittance (AVT) of 22% and power conversion efficiency (PCE) of 8.20%. Considering required AVT for the application of power-generating window of ∼25% and recent reports, this result is one of the best performances reported to date.

As an alternative hole transport layer (HTL) to poly(3,4-ethylendioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), we investigated V2O5 thin films fabricated by simple brush painting without any post-treatments. Polymer solar cells (PSCs) with V2O5 fabricated by brush painting showed superior performance to that of conventional PEDOT:PSS based system; in particular, higher FF was obtained. Because more hydrophobic oxide surface induces better physical contact and better wetting of active blends, lower RS is obtained; thus, the resulting device shows higher performance. PSC with brush painted V2O5 at 50 °C using 0.99 vol% vanadium (V) oxytriisopropoxide in isopropyl alcohol exhibited the best power conversion efficiency (PCE) of 3.83%. Furthermore, employment of V2O5 as HTL leads to significant improvement in long-term stability in air (dropping of PCE of conventional PEDOT:PSS system to ~0% and retention of PCE of V2O5 based PSC to over 60% after exposure in air for 96 h without any encapsulation).

In this work, we have demonstrated that simple brush-painted Ti-doped In2O3(TIO) films can be used as a cost effective transparent anodes for organic solar cells (OSCs). By the direct brushing of TIO nanoparticles ink and rapid thermal annealing (RTA), we can simply obtain TIO electrodes with a low sheet resistance of 28.25 Ω/□ and a high optical transmittance of 85.48% under atmospheric ambient conditions. In particular, the brush painted TIO films showed a much higher mobility (33.4 cm2/V s) than that of previously reported solution-process transparent oxide films (1–5 cm2/V s) due to the effects of the Ti dopant with higher Lewis acid strength (3.06) and the reduced contact resistance of TIO nanoparticles. The OSCs fabricated on the brush-painted TIO films exhibited cell-performance with an open circuit voltage (Voc) of 0.61 V, shot circuit current (Jsc) of 7.90 mA/cm2, fill factor (FF) of 61%, and power conversion efficiency (PCE) of 2.94%. This indicates that brush-painted TIO film is a promising cost-effective transparent electrode for printing-based OSCs with its simple process and high performance.

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 100 mW cm−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.

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.

We demonstrate that pitch-converted carbon nanosheet (CNS) films can efficiently function as transparent conducting electrodes for polymer solar cells (PSCs). The solution-processed CNS film was prepared with spin-coating of a cost-effective pitch solution dissolved in dimethylformamide on quartz substrates, followed by stabilization and carbonization treatments to convert the pitch into CNS. The pitch-converted CNS films prepared by the successive heat-treatment process were examined as a novel transparent anode in solar cells, and as a result, PSCs fabricated directly on such CNS electrodes exhibited a high power conversion efficiency of ∼1.7% under 100 mWcm −2 illumination and AM 1.5 G conditions. This approach could be highly desirable for advancing the realization of fully printable and flexible low-cost transparent electrodes for indium tin oxide (ITO)-free polymer solar cells.

We report an effective 2-step solvent treatment combined with a polar solvent vapor annealing process (PSVA) and a dipping process using polar solvents (DP) to enhance the electrical conductivity of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films, which is highly desirable for the fabrication of solution-processed organic photovoltaics (OPVs) on flexible substrates. The PSVA and DP-treated PEDOT:PSS films showed conductivities up to 1475 S/cm. The changes in conductivity, surface morphology, composition, and conformational PEDOT chains are investigated to elucidate the effect of the 2-step PSVA and DP treatment on PEDOT:PSS films. The highly segregated-PSS component induced by PSVA was effectively removed from the PEDOT:PSS films after successive DP treatments, eventually resulting in an enhanced conductivity of bulk films. We also employed optimized PEDOT:PSS films treated by the 2-step PSVA and DP-process as transparent anodes for indium tin oxide (ITO)-free OPVs fabricated on flexible substrates. The device performance of flexible OPVs with PSVA and DP-treated films was further improved due to the increased conductivity and decreased series resistance of devices and showed highly comparable cell-efficiency with ITO-based flexible OPVs. These results suggest that the 2-step solvent-treated PEDOT:PSS film is a promising alternative to ITO for realization of high-efficiency, flexible, and low-cost ITO-free OPVs with facile manufacturing process.

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.

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 63.3 O/squares, respectively, corresponding to an increase in film thickness. The best device exhibited a high power conversion efficiency of 2.17% under 100 mW cm 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.

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.

The preparation and characteristics of flexible indium tin oxide (ITO) electrodes grown on polyethylene terephthalate (PET) substrates using a specially designed roll-to-roll sputtering system for use in flexible organic solar cells are described. It was found that both electrical and optical properties of the flexible ITO electrode were critically dependent on the Ar/O2 flow ratio in the continuous roll-to-roll sputter process. In spite of the low substrate temperature (o501C), we can obtain the flexible ITO electrode with a sheet resistance of 47.4O/square and an average optical transmittance of 83.46% in the green region of 500–550 nm wavelength. Both X-ray diffraction and field emission scanning electron microscopy analysis results showed that all flexible ITO electrodes grown on the PET substrate were amorphous with a very smooth and featureless surface, regardless of the Ar/O2 flow ratio due to the low substrate temperature, which is maintained by a cooling drum. In addition, the flexible ITO electrode grown on the Ar ion-beam-treated PET substrates showed more stable mechanical properties than the flexible ITO electrode grown on the wet-cleaned PET substrates, due to an increased adhesion between the flexible ITO and the PET substrates. Furthermore, the flexible organic solar cell fabricated on the rollto-roll sputter-grown flexible ITO electrode at an optimized condition exhibited a power conversion efficiency of 1.88%. This indicates that the roll-to-roll sputtering technique is a promising continuous

A new type of counter electrode comprising of Pt and NiO biphase was prepared an RF magnetron cosputtering system for a dye-sensitized solar cell (DSSC). Transmission electron microscope images, transmission electron diffraction patterns, and X-ray diffraction patterns of the Pt–NiO electrodes confirmed the formation of a nanosized Pt polycrystalline phase of ∼7 nm mixed with porous amorphous NiO phase. The short-circuit current density and cell efficiency were increased from 0.22 to 0.30 mA/cm 2 and from 2.1% to 2.8%, respectively, and almost constant open-circuit voltage and fill factor, 0.53 V and 63%, respectively, were observed.

TiO2/ZnO/Eosin Y structure films were prepared by a one-step cathodic electrodeposition method and used as a photoanode in a dye-sensitized solar cell (DSSC). Using this TiO2/ZnO/Eosin Y electrode in DSSC, the degradation of the cell with time was reduced and ISC, VOC and fill factor values were increased. The use of a thin ZnO layer, permitted the formation of an energy barrier at the electrode/electrolyte interface, thus reducing recombination rate and improving cell performance. In addition, the adsorbed dye molecules prepared by one-step cathodic electrodeposition with ZnO were very stable compared with that prepared by conventional immersing method, as evidenced by UV/vis absorption spectroscopy measurements.