CN103165814A - Organic photovoltaic device based on calcium halide cathode buffer layer and its preparation method - Google Patents

Abstract

The invention provides an organic photovoltaic device based on a calcium halide cathode buffer layer and a preparation method of the organic photovoltaic device. The organic photovoltaic device is prepared by introducing a method using calcium halide as a cathode buffer layer, a quenching effect of a metal cathode on an exciton in an organic functional layer is effectively reduced, the contact barrier of the metal cathode and the organic functional layer is reduced, and the photovoltaic performance of the organic photovoltaic device is effectively improved.

Description

Organic photovoltaic device based on calcium halide cathode buffer layer and its preparation method

technical field

The invention belongs to the field of organic photovoltaics, and in particular relates to a novel organic photovoltaic device with a cathode buffer layer and a preparation method thereof.

Background technique

The structure of organic photovoltaic (OPVs) devices mainly includes an anode, an organic functional layer and a cathode. When the device is illuminated, the donor material in the organic functional layer is excited to generate excitons (electron-hole pairs), and the excitons diffuse to the interface between the donor material and the acceptor material, under the action of the built-in electric field at the interface , the holes and electrons are separated. The holes are transported in the donor material and collected by the anode, and the electrons are transported in the acceptor material and collected by the cathode, thereby generating the photovoltaic effect. In order to improve device performance, a buffer layer is usually prepared between the cathode and the organic functional layer to improve the contact between the organic layer and the cathode, reduce the barrier between the organic functional layer and the cathode, and ultimately optimize the performance of OPVs devices.

At present, the cathode buffer layer is generally made of alkali metal fluoride, such as LiF film layer [H.Heil et al. Journal of Applied Physics, 105(2009), 073105.], this method can effectively improve the electron collection efficiency. In addition, organic matter can also be used as a cathode buffer layer, such as the classic electron blocking layer material BCP, which can act as a cathode buffer layer for photovoltaic devices [C.C.Chang et al. Applied Physics Letters, 96(2010), 263506.], effectively preventing organic The attenuation of device performance caused by the diffusion of C atoms in the functional layer to the cathode improves the device performance.

The contact between organic semiconductor materials and metals is often not an ohmic contact, which will increase the contact barrier between the organic layer and the metal electrode, increase the series resistance of the device, and then reduce the photovoltaic performance of the device. In addition, a chemical reaction may occur between the electrode and the organic functional layer, or the metal electrode has a strong quenching effect on the excitons in the organic functional layer, which will also lead to the attenuation of the performance of the photovoltaic device. Therefore, the introduction of a cathode buffer layer is crucial to improve the performance of organic photovoltaic devices.

Contents of the invention

The present invention finds a new type of cathode buffer layer—calcium halide, and applying it to organic photovoltaic devices can effectively improve device performance.

Technical scheme of the present invention is as follows:

An organic photovoltaic device based on a calcium halide cathode buffer layer, comprising an anode, an anode buffer layer, an organic functional layer, a cathode buffer layer and a cathode, the cathode buffer layer is calcium halide, and its thickness range is 0.25nm-1.5nm, Preferably 0.5 nm.

The material used for the anode buffer layer may be poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) (PEDOT:PSS), with a thickness of 28 nm. PEDOT:PSS is one of the most commonly used anode buffer layers in organic photovoltaic devices.

The above-mentioned organic functional layer can use a mixed solution of poly 3-hexylthiophene (P3HT) and [6,6]-phenyl-C ₆₁ -butyric acid methyl ester (PC ₆₁ BM) as a spin-coating material, and the thickness of the organic functional layer is controlled at Around 100nm. P3HT:PC ₆₁ BM bulk heterojunction organic functional layer is one of the organic functional layers frequently used in organic photovoltaic devices.

The above-mentioned cathode buffer layer may be calcium halide, including CaCl ₂ , CaBr ₂ , CaF ₂ and CaI ₂ .

The above-mentioned cathode materials include but are not limited to aluminum, magnesium-silver alloy, lithium-aluminum alloy, calcium-aluminum alloy, calcium-silver alloy and silver, and the thickness of the cathode is controlled at about 100 nm.

A method for preparing an organic photovoltaic device based on a calcium halide cathode buffer layer, comprising the following steps:

1) Make an anode buffer layer on the anode;

2) Fabricate an organic functional layer on the anode buffer layer;

3) Fabricate a cathode buffer layer on the organic functional layer;

4) Evaporate metal electrodes on the cathode buffer layer.

The organic layers (including anode buffer layer, organic functional layer) and cathode buffer layer in the device are produced by vacuum evaporation or solution spin coating, which are well known to those skilled in the art and will not be repeated here.

The present invention effectively weakens the quenching effect of the metal cathode on the excitons in the organic functional layer by introducing calcium halide into the cathode buffer layer, and reduces the contact barrier between the metal cathode and the organic functional layer. In addition, the calcium halide film layer can be regarded as The dipole layer can improve the electron collection efficiency of the metal cathode.

Description of drawings

Fig. 1a is a schematic structural diagram of a reference device 1; Fig. 1b is a schematic structural diagram of a reference device 2; Fig. 1c is a schematic structural diagram of an OPVs device 1 of the present invention.

Fig. 2 is the current density-voltage curves of reference device 1, reference device 2 and inventive devices based on different thicknesses of _CaCl2 layers as cathode buffer layers.

Detailed ways

The method for improving the performance of OPVs devices of the present invention will be described in detail below in conjunction with the accompanying drawings, but it does not constitute a limitation of the present invention.

1. Preparation of reference device 1:

1) Cleaning ITO (Indium Tin Oxide): Ultrasonic cleaning in deionized water, acetone, and ethanol for 10 minutes respectively, drying with nitrogen, and then treating in an oxygen plasma cleaner for 5 minutes;

2) The anode buffer layer PEDOT:PSS aqueous solution is spin-coated on the anode ITO, the rotation speed is 2500r/min, and the spin-coating time is 30s. Anneal in a nitrogen atmosphere at an annealing temperature of 200°C for 20 min, and then slowly drop to room temperature.

3) Spin-coat the organic functional layer P3HT:PC ₆₁ BM mixed solution (P3HT:PC ₆₁ BM=15:12mg/ml mixed solution) on the anode buffer layer, spin-coating speed 900r/min, time 15s. Anneal in a nitrogen atmosphere at an annealing temperature of 150° C. for 10 min, and then slowly drop to room temperature.

4) Vacuum-evaporating cathode Al on the organic functional layer with a thickness of 100 nm.

The device structure is shown in Figure 1a.

2. Preparation of reference device 2:

1) Cleaning ITO: ultrasonic cleaning in deionized water, acetone and ethanol for 10 minutes respectively, drying with nitrogen, and then processing in an oxygen plasma cleaning instrument for 5 minutes; solution spin-coating anode buffer layer PEDOT on the anode ITO: PSS, speed 2500r/min, time 30s. Anneal in a nitrogen atmosphere at an annealing temperature of 200°C for 20 min, and then slowly drop to room temperature.

2) Spin-coat the organic functional layer (mixture of P3HT:PC ₆₁ BM=15:12mg/ml) on the anode buffer layer with a rotating speed of 900r/min for 15s. Anneal in a nitrogen atmosphere at an annealing temperature of 150° C. for 10 min, and then slowly drop to room temperature.

3) Vacuum-deposit a cathode buffer layer LiF on the organic functional layer with a thickness of 0.7 nm.

4) Vacuum-evaporating cathode Al on the cathode buffer layer with a thickness of 100 nm.

The device structure is shown in Figure 1b.

3. Preparation of OPVs device 1 of the present invention:

1) Cleaning ITO: Ultrasonic cleaning in deionized water, acetone, and ethanol for 10 minutes respectively, drying with nitrogen, and then processing in an oxygen plasma cleaning instrument for 5 minutes;

2) Spin-coat the anode buffer layer PEDOT:PSS on the anode ITO with a rotation speed of 2500r/min for 30s. Anneal in a nitrogen atmosphere at an annealing temperature of 200°C for 20 min, and then slowly drop to room temperature.

3) On the anode buffer layer, the organic functional layer (mixture of P3HT:PC ₆₁ BM=15:12mg/ml) was spin-coated with a rotating speed of 900r/min for 15s. Anneal in a nitrogen atmosphere at an annealing temperature of 150° C. for 10 min, and then slowly drop to room temperature.

左右，CaCl₂膜层厚度分别是0.25nm、0.5nm、1nm和1.5nm，共四类器件。4) When the vacuum degree is lower than 3×10 ^-4 Pa, the cathode buffer layer CaCl ₂ is vacuum evaporated on the organic functional layer, and the evaporation rate is controlled at

Left and right, the thickness of the CaCl ₂ film is 0.25nm, 0.5nm, 1nm and 1.5nm respectively, and there are four types of devices in total.

5) Vacuum-evaporating cathode Al on the cathode buffer layer with a thickness of 100 nm.

The structure of OPVs device is shown in Figure 1c.

4. Preparation of OPVs device 2 of the present invention:

1) Cleaning ITO: Ultrasonic cleaning in deionized water, acetone, and ethanol for 10 minutes respectively, drying with nitrogen, and then processing in an oxygen plasma cleaning instrument for 5 minutes;

2) Spin-coat the anode buffer layer PEDOT:PSS on the anode ITO with a rotation speed of 2500r/min for 30s. Anneal in a nitrogen atmosphere at an annealing temperature of 200°C for 20 min, and then slowly drop to room temperature.

3) On the anode buffer layer, the organic functional layer (mixture of P3HT:PC ₆₁ BM=15:12mg/ml) was spin-coated with a rotating speed of 900r/min for 15s. Anneal in a nitrogen atmosphere at an annealing temperature of 150° C. for 10 min, and then slowly drop to room temperature.

左右，CaF₂膜层厚度是0.25nm。4) When the vacuum degree is lower than 3×10 ^-4 Pa, the cathode buffer layer CaF ₂ is vacuum evaporated on the organic functional layer, and the evaporation rate is controlled at

Around, the thickness of CaF ₂ film is 0.25nm.

5) Vacuum-evaporating cathode Al on the cathode buffer layer with a thickness of 100 nm.

5. Preparation of OPVs device 3 of the present invention:

1) Cleaning ITO: Ultrasonic cleaning in deionized water, acetone, and ethanol for 10 minutes respectively, drying with nitrogen, and then processing in an oxygen plasma cleaning instrument for 5 minutes;

2) Spin-coat the anode buffer layer PEDOT:PSS on the anode ITO with a rotation speed of 2500r/min for 30s. Anneal in a nitrogen atmosphere at an annealing temperature of 200°C for 20 min, and then slowly drop to room temperature.

3) On the anode buffer layer, the organic functional layer (mixture of P3HT:PC ₆₁ BM=15:12mg/ml) was spin-coated with a rotating speed of 900r/min for 15s. Anneal in a nitrogen atmosphere at an annealing temperature of 150° C. for 10 min, and then slowly drop to room temperature.

左右，CaBr₂膜层厚度是0.5nm。4) When the vacuum degree is lower than 3×10 ^-4 Pa, the cathode buffer layer CaBr ₂ is vacuum evaporated on the organic functional layer, and the evaporation rate is controlled at

Around, the CaBr ₂ film thickness is 0.5nm.

5) Vacuum-evaporating cathode Al on the cathode buffer layer with a thickness of 100 nm.

6. Preparation of OPVs device 4 of the present invention:

1) Cleaning ITO: Ultrasonic cleaning in deionized water, acetone, and ethanol for 10 minutes respectively, drying with nitrogen, and then processing in an oxygen plasma cleaning instrument for 5 minutes;

2) Spin-coat the anode buffer layer PEDOT:PSS on the anode ITO with a rotation speed of 2500r/min for 30s. Anneal in a nitrogen atmosphere at an annealing temperature of 200°C for 20 min, and then slowly drop to room temperature.

3) On the anode buffer layer, the organic functional layer (mixture of P3HT:PC ₆₁ BM=15:12mg/ml) was spin-coated with a rotating speed of 900r/min for 15s. Anneal in a nitrogen atmosphere at an annealing temperature of 150° C. for 10 min, and then slowly drop to room temperature.

4) The cathode buffer layer CaI ₂ is spin-coated on the organic functional layer, the spin-coating speed is 4000 rpm, the spin-coating time is 60 seconds, and the thickness of the CaI ₂ film layer is controlled at 1.0nm.

5) Vacuum-evaporating cathode Al on the cathode buffer layer with a thickness of 100 nm.

7. Measurement of photovoltaic performance of each device:

Under the light conditions of the solar simulator (Newport Thermal Oriel69911300W) AM1.5G100mW/ ^cm2 , each device generates a photocurrent, and the current density-voltage data is recorded with a Keithley2611source meter. The measurement results are shown in Figure 2. The above results are summarized in Table 1.

Table 1. Photovoltaic performance parameters of reference device 1, reference device 2 and inventive devices based on different thicknesses of _CaCl2 layer as cathode buffer layer

(FF = fill factor; PCE = power conversion efficiency; V _oc = open circuit voltage; J _sc = short circuit current density)

As shown in Table 1, the photovoltaic performance of the inventive device is greatly improved compared with the reference device 1. When the thickness of CaCl ₂ is 0.5nm, the power conversion efficiency (PCE) of the inventive device is increased to 2.85%, and the fill factor (FF ) to 0.64 and the open circuit voltage (V _oc ) to 0.59V. In addition, the photovoltaic performance of the inventive device is not inferior to that of the reference device 2 based on the LiF cathode buffer layer. Therefore, calcium halide is a good cathode buffer layer material, which can effectively improve the photovoltaic performance of organic photovoltaic devices.

The application of the calcium halide provided by the present invention in improving the collection efficiency of metal cathodes to electrons in organic photovoltaic devices and its preparation method have been described above through detailed examples. Within, certain deformation or modification can be made to the device structure of the present invention, and its preparation method is not limited to the content disclosed in the embodiment.

Claims (8)

1. An organic photovoltaic device based on a calcium halide cathode buffer layer, comprising an anode, an anode buffer layer, an organic functional layer, a cathode buffer layer and a cathode, and the cathode buffer layer is calcium halide. 2. The organic photovoltaic device according to claim 1, characterized in that the calcium halide has a thickness of 0.25nm-1.5nm. 3. The organic photovoltaic device according to claim 1, wherein the material used for the anode buffer layer is poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid). 4. The organic photovoltaic device according to claim 1, characterized in that, the material used for the organic functional layer is poly-3-hexylthiophene and [6,6]-phenyl-C _61- butyric acid methyl ester mixed solution . 5 . The organic photovoltaic device according to claim 1 , wherein the calcium halide comprises CaCl ₂ , CaBr ₂ , CaF ₂ and CaI ₂ . 6. The organic photovoltaic device according to claim 1, wherein the cathode material comprises aluminum, magnesium-silver alloy, lithium-aluminum alloy, calcium-aluminum alloy, calcium-silver alloy and silver. 7. The preparation method of the arbitrary described organic photovoltaic device of claim 1-6, comprises the following steps: 1) Make an anode buffer layer on the anode; 2) Fabricate an organic functional layer on the anode buffer layer; 3) Fabricate a cathode buffer layer on the organic functional layer; 4) Evaporate metal electrodes on the cathode buffer layer. 8. The preparation method according to claim 7, wherein the above-mentioned anode buffer layer, organic functional layer and cathode buffer layer are prepared by vacuum evaporation or solution spin coating.

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