Flexible and Transparent Electrodes of Cu_2−XSe with Charge Transport via Direct Tunneling Effect

Abstract

New generations of organic semiconducting devices have driven the search to replace the well-established indium-doped tin oxide (ITO) and fluorine-doped tin oxide (FTO) electrodes. [1,2] The requirements for alternative materials include a high electrical conductivity and possibility to prepare thin, transparent and flexible films with large areas at low cost. ITO is used as anode in organic light-emitting diodes (OLEDs) due to its transparency in the visible region and high conductivity (>10 3 S cm −1 ). However, the high Schottky barrier on ITO (or FTO) interfaces makes it difficult to inject charge carriers into the active semiconducting layer, especially because of its work function of ≈4.4 eV. [3] This problem can be mitigated by treating its surface to alter the working function or by inserting intermediate layers to change electron mobility and promote a better balance between the injected charge carriers. [4] Another possibility is to employ chalcogenide metals such as copper selenide that can exist in different compositions, namely stoichiometric Cu 2 Se, Cu 3 Se 2 , CuSe, and CuSe 2 and non-stoichiometric Cu 2−X Se. [5][6][7][8][9] The latter is a p-type semiconductor with an energy gap of ≈2.3 eV and work function of 4.17 eV, therefore promising as a hole-injecting electrode for OLEDs. [7,[9][10][11] Films of Cu 2−X Se can be prepared with vacuum evaporation, [12,13] cation-anion combination, [14][15][16] cation-anion combination in hot coordinating solvents, [17][18][19] element combination in the solid state, [20] galvanic synthesis, [21] chemical reduction from CuSe, [22] electrochemical methods, [23] and chemical bath deposition. [24][25][26] We demonstrate here that Cu 2−X Se films can function as electrodes for organic electronics. The films were synthesized from copper deposited from the vapor phase followed by chemical bath deposition. With polyester as substrate, the resulting films are flexible, thin and transparent. For comparison, devices with an FTO electrode are also discussed. Poly-[2-methoxy-5-(2ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) was used in a light-emitting inorganic-organic hybrid diode (IOHLED). The effectiveness of Cu 2−X Se as electrode was demonstrated in a comparison with a device containing an intermediate layer of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) In this paper, it is demonstrated that copper selenide (Cu 2−X Se) films onto polyester sheets may serve as transparent electrodes in inorganic-organic hybrid light emission devices (IOHLED), as possible replacement to indium tin oxide or fluorine-doped tin oxide. The Cu 2−X Se film synthesized via bath chemical deposition is electrically stable with a sheet resistance of 148 Ω sq −1 and optical bandgap of 2.3 eV. IOHLED are made with poly(3,4ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) as an organic layer for hole transport and poly[2-metoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) as electroluminescent semiconductor. The IOHLED emits in the visible range owing to the simu...

Infrared Laser‐Induced Graphene Sensor for Tyrosine Detection

“…The Raman spectrum was performed in a Horiba Confocal LabRAM HR Evolution microscope employing a green laser (λ=532 nm) with 2 mW of power. The LIG conductivity was determined using the same experimental array (four‐point method) reported by Silva et al ., [48] considering the LIG thickness and area of 50 μm and 0.342 cm 2 , respectively; and correction factor of 0.9994.…”

“…The LIG conductivity was determined using the same experimental array (four-point method) reported by Silva et al, [48] considering the LIG thickness and area of 50 μm and 0.342 cm 2 , respectively; and correction factor of 0.9994.…”

Characterization of Flexible Copper Selenide Films on Polyamide Substrate Obtained by SILAR Method—Towards Application in Electronic Devices

“…The stoichiometric composition of copper selenide strongly influenced its crystalline structure and electronic behavior-it alters its electronic, chemical, and thermal properties [4,5]. Copper-deficient Cu 2−x Se is an intrinsic p-type semiconductor with direct bandgap energies in the range of 2.0 to 2.4 eV, the work function of 4.17 eV, and high photo-electrochemical conversion efficiency (~14.6%) [3,[5][6][7][8]. These features of Cu 2−x Se can be used as Shottky diodes [9], self-repairable electrodes [10], and photovoltaic devices [8].…”

“…When Cu 2−x Se is deposited on a flexible transparent polymer substrate (polyvinylchloride, polyvinyl alcohol), the possibility of using thin flexible polymer substrates appears in the fabrication of flexible optoelectronic devices [26]. Cu 2−x Se films on polyester sheets can be used as a transparent electrode for inorganic and organic hybrid light emitters, as a possible replacement for indium tin oxide or fluorine-doped tin oxide [7].…”

Microwave-assisted hydrothermal synthesis of copper selenides (Cu2−x Se) thin films for quantum dots-sensitized solar cells

“…Copper selenide can exist in a wide range of stoichiometric (CuSe, Cu 2 Se, CuSe 2 , Cu 3 Se 2 , etc) and non-stoichiometric compositions (Cu 2−x Se) [12,13], and can be constructed into several crystallographic forms (monoclinic, cubic, hexagonal, etc) with different bandgaps [14,15]. To date, considerable research efforts have been devoted to the preparation of copper selenide, and a series of synthesis approaches have also been developed such as chemical bath deposition [16], hydrothermal method [17], electrochemical deposition [9], hot injection approach [12], and microwave irradiation method [18].…”