KR20190129166A - Smallmolecule organic photovoltaic modules and method for manufacturing the same - Google Patents

Abstract

Disclosed are a large-area monomolecular organic photovoltaic module to which a halogen-free solvent-based slot die coating method is applied, and a method for manufacturing the same. The organic photovoltaic module according to the present invention can exhibit a large area and excellent power conversion efficiency (PCE) by applying a slot die coating method based on a halogen-free solvent. The method for manufacturing a monomolecular organic photovoltaic module includes the following steps: (a) preparing a substrate on which a patterned metal oxide is formed; (b) forming a conductive polymer layer on the substrate formed with a patterned metal oxide; (c) forming an active layer including a single molecule on the conductive polymer layer; (d) forming metal on the active layer to manufacture a monomolecular organic solar cell; and (e) preparing the solar cell in plural numbers, and connecting the solar cells in series to manufacture a monomolecular organic photovoltaic module.

Description

Monomolecular organic photovoltaic module and its manufacturing method {SMALLMOLECULE ORGANIC PHOTOVOLTAIC MODULES AND METHOD FOR MANUFACTURING THE SAME}

The present invention relates to an organic photovoltaic module, and more particularly, to a technique for manufacturing a large-area single-molecule photovoltaic module by applying a halogen-free solvent-based slot die coating method.

Bulk heterojunction organic solar cells (OSCs), composed of electron donor and electron acceptor materials, have been regarded as next-generation photovoltaic technologies because of their high throughput, low cost mass production, as well as their potential for flexibility and light weight.

In particular, single molecules, one of the organic conjugated molecules, have recently been attracting attention from researchers and have developed advanced technologies. As a result, more than 10% power conversion efficiency (PCE) was achieved for monomolecular-based organic solar cells, reaching a threshold for practical use. Unlike polymers, single molecules are well-defined molecular structures, high purity and less batch-to-batch variation, making them more suitable candidates for industrial applications.

However, despite the promising nature and the rapid development of PCE, few studies have focused on the production of monomolecular solar cells using roll-to-roll compatible printing technology.

However, with the accelerated growth of current monomolecular solar cells, the performance of printed large area devices to reduce the research gap between monomolecular and polymeric materials should be achieved in this field. In order to realize the practical use of OSCs, the successful demonstration of photovoltaic devices by the printing method is essential for the roll-to-roll process.

In addition, in the continuous roll-to-roll process, the optimum form of the blend film must be obtained without time-consuming thermal annealing or solvent vapor annealing (SVA) processes. Unfortunately, many high performance monomolecular solar cells have been shown to require this time consuming post treatment.

However, in order to meet the requirements for the manufacture of large area devices and for further industrial production, the above-mentioned method should be replaced by a more appropriate method that can simplify the production stage (eg the introduction of additives into the solution). .

Therefore, proper processing and printing techniques must be considered for future upscaling of OSC.

Another problem with commercial viability is the toxicity of commonly used organic solvents. To date, most OSCs have been processed from organic solvents containing halogen atoms such as chloroform, chloro benzene (CB) and dichloro benzene (DCB). It is well known that OSCs based on halogenated solvents are advantageous in achieving good performance due to moderate solubility than those based on non-halogenated solvents.

However, the detrimental nature of halogenated solvents, expensive synthesis and removal steps serve as a barrier from a manufacturing standpoint.

In this regard, efforts have recently been made to replace halogenated solvents in spin-coated monomolecular solar cells with more environmentally friendly halogen free solvents.

An object of the present invention is to provide a large-area monomolecular organic photovoltaic module applying a halogen-free solvent-based slot die coating method.

The organic photovoltaic module according to the present invention can exhibit a large area and excellent power conversion efficiency (PCE) by applying a slot die coating method based on a halogen-free solvent.

1 shows (a) active layer components, BTR and PC71BM. (b) Schematic of slot die coating. (c) Chemical structure of non-halogen solvents and additives.
2 shows (a) current density-voltage curves of slot die coated OSC treated under various conditions. (b) corresponding EQE and (c) UV-vis absorption spectra. Inset picture is a photographic image of an organic thin film.
3 is a TEM image of (a) AFM and (b) slot die coated blend film.
4 is a current density-voltage graph for (a) hole only and (b) electron only devices.
5 shows (a) a 2D GIXRD image of a slot die coated blend film and (b) a line cut profile out of the plane. (c) Relationship between donor (100) peak intensity and photovoltaic parameters, J _sc and FF.
6 shows (a) a photographic image of a slot die coated large area photovoltaic module during the printing process and (b) the corresponding current density-voltage curve of the champion cell.

Advantages and features of the present invention and methods for achieving them will be apparent with reference to the embodiments described below in detail with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in various forms, and only the present embodiments are intended to complete the disclosure of the present invention, and the general knowledge in the art to which the present invention pertains. It is provided to fully convey the scope of the invention to those skilled in the art, and the present invention is defined only by the scope of the claims. Like reference numerals refer to like elements throughout.

Hereinafter, a monomolecular organic photovoltaic module and a method for manufacturing the same according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

In the present invention, a large area monomolecular photovoltaic module was manufactured by applying a halogen-free solvent-based slot die coating method.

Here, a mixed film composed of BTR (benzodithiophene terthiophene rhodanine) and [6.6] -phenyl-C71-butyric acid methyl ester (PC71BM) was used as the active layer.

As a result, slot die printed monomolecular solar cells with time-consuming SVA processing and a roll-to-roll compatible approach resulted in 7.46% and 6.56% PCE, respectively.

Finally, the roll-to-roll compatibility method was extended to fabrication of a large area photovoltaic module consisting of 4 stripes of 10 cm ² total effective area, yielding 4.83% PCE. This is for printed photovoltaic modules composed of monomolecular materials.

The electron donor and electron acceptor material structures of the mixed film are shown in FIG. 1A. One of the commercially available monomolecules, BTR, was previously reported to have a high efficiency of 9.3% from the spin coating method in N ₂ atmosphere with the SVA process.

However, in this study, as demonstrated in FIG. 1B, monomolecular solar cells were demonstrated by slot die coating in the atmosphere. Non-halogen solvents were used instead of halogenated solvents for applications in more preferred large area photovoltaic modules. More importantly, there is also a need for an alternative method for replacing time-consuming SVA post-treatment with a roll-to-roll compatible process, such as the introduction of solvent additives.

In this study, environmentally friendly non-halogenated molecules were also used as additives to produce morphological control similar to those found in SVA.

1C shows the molecular structure of the halogen free solvents and additives used in this study. As a result, slot die printed monomolecular solar cells could be processed using a roll-to-roll compatible approach based on halogen-free systems.

To confirm the effectiveness of the roll-to-roll compatible approach, slot die printing devices were fabricated with the general structure of ITO / PEDOT: PSS / BTR: PC71BM / Ca / Al.

Three types of devices were prepared for comparison. Any untreated as-cast film, a film after SVA treatment, or a blend film treated with diphenyl ether (DPE) additive can be used. The current density-voltage characteristics of these devices are shown in FIG. 2A and the corresponding photovoltaic parameters are summarized in [Table 1].

TABLE 1

As expected, the cast film without any treatment showed a low PCE of 3.81%. However, in line with previous reports, the performance of the device was significantly improved to a maximum PCE of 7.46% through SVA treatment with tetrahydrofuran (THF) solution.

Devices treated with DPE additives showed a similar trend, improving performance due to a significant increase in the fill factor (FF) and short circuit current (J _sc ), despite a slight drop in circuit voltage (Voc).

As a result, a device treated with a non-halogenated DPE additive could achieve a maximum PCE of 6.56% with VOC 0.90 V, Jsc 11.2 mA cm ^-2 , FF 69.6%.

These results suggest that the method associated with DPE, a roll-to-roll compatible approach, could ideally be converted to the manufacture of large-area solar modules.

External quantum efficiency (EQE) was measured to determine the reason for Jsc improvement after SVA treatment and introduction of DPE additives. As can be seen in FIG. 2B, all devices treated under various conditions exhibit a wide range of photocurrent response in the wavelength range from 350 nm to 700 nm. However, compared to as-cast films, both SVA and DPE-added films showed improved EQE intensity than in the longer wavelength range. The maximum EQE peaks of the cast, SVA and DPE added films were determined to be 53%, 68% and 61%, respectively.

Thus, an improved Jsc value consistent with the integrated current density from the EQE spectrum within 5% error may be the result of the efficient conversion of incident light into photocurrent.

2C shows the UV-vis absorption spectrum of the thin film. Remarkably, films made under different treatment conditions showed similar absorption spectral trends as the EQE spectrum. However, from the UV-vis absorption spectrum the appearance of the shoulder peaks (about 615 nm) for the SVA and DPE-added films could be observed more clearly. As a result, we can suggest intensive intermolecular interactions of the donor phase for SVA and DPE-added films. In addition, this change in optical properties can be easily distinguished by the color change of the thin film, as revealed in the photographic image (illustration of FIG. 2C). In this case, the DPE-additive introduction film was almost identical to the SVA treated film, and the cast film showed a considerably different color. The surface and bulk morphology of the mixed membranes were investigated using atomic force microscopy (AFM) and transmission electron microscopy (TEM) measurements.

As shown in FIG. 3A, SVA and DPE-added films have coarse domains with increased root mean square (RMS) roughness of 0.74 nm and 0.77 nm, in contrast to the cast film having an RMS value of 0.26 nm. Indicated. In addition, from the TEM image, it can be seen that both the SVA-treated film and the DPE-added film are properly separated in phase separation having a large domain compared to the cast film. As is well known, the evolution of large domains with relatively low grain boundaries facilitates high exciton dissociation and good charge transport due to reduced charge carrier-recombination centers. Thus, improved J _sc and FF can be provided for both films. These similar morphological properties of the two blend films indicate that the roll-to-roll compatible approach associated with the introduction of DPE necessarily provides a morphological development comparable to time-consuming SVA treatment. Improvements in J _sc and FF in SVA and DPE additive conditions were supported by the space-charge limiting current (SCLC) model (FIG. 4). For SVA and DPE-added films, improved charge carrier mobility was calculated over the cast film than in the current density-voltage curve. The higher hole and electron mobility (μh and μe) of both films is in good agreement with the improved J _sc . In addition, more balanced electron and hole mobility can be obtained with both SVA and DPE added films. For example, the electron and hole mobility ratios (μe / μh) of SVA and DPE added films were reduced to 2.41 and 3.76 of cast film (5.75), respectively. A better charge balance between electrons and holes is clear evidence of the high FF value of ca (70%).

Thus, the improvement of J _sc and FF in SVA and DPE additive conditions can be explained by improved and balanced charge carrier transport with the formation of continuous percolation pathways identified by AFM and TEM images. Charge carrier recombination behavior has been explained by measuring Voc as a function of incident light intensity (FIG. 3). All films exhibit strong Voc dependence on light intensity, indicating the presence of non-germination recombination processes.

However, the cast film, in particular, exhibited greater tilt values compared to the other two films at low luminosity (10 mW / cm ² or less).

Thus, it was concluded that SVA and DPE-added films had a relatively reduced trap-assisted recombination loss compared to as-cast films.

To further investigate the molecular orientation of the slot die printed film, grazing incidence wide-angle X-ray scattering (GIWAXS) measurements were performed on the raw and mixed films.

The BTR has a π-π stacking due to its high crystallinity (presenting a clear edge-on direction with maximum layer reflection (h00) reflection up to third order in the out-of-plane direction with π-π stacking).

In contrast, the neat PC71BM film showed a ring-shaped pattern showing isotropic and disordered structures. After mixing together, the texture of the as-cast film became similar to the mixture of the two neat films as shown in FIG. 5A.

In other words, the as-cast film retained edge-on orientation with little change in placement. However, further noticeable π-π stacking (010) peaks were observed at q = 1.68 Hz-1 in the out-plane direction after SVA treatment, suggesting the occurrence of the frontal direction.

As a result, the SVA film can achieve both edge on and face on directions to enable effective three dimensional (3D) charge transport. Similarly, the DPE-added films also exhibited π-π stacking (010) peaks in the out-of-plane direction.

Thus, from these results, the introduction of halogen-free DPE additives has been found to lead to the formation of optimal morphology as well as beneficial coexisting orientations.

5B shows the out-of-plane line cut profile of the GIWAXS image. Here, all line cut profiles were normalized based on PC71BM peak intensity located at q = 1.35 dB ⁻¹ . Thus, for SVA and DPE-added films, we observed much sharper donor peaks with increased intensity, which is in good agreement with the UV-visible absorption spectrum.

)에 비해 17.9Å의 라멜라 (100) 거리가 더 감소됨을 나타내었다.This (100) peak intensity for each condition has a good correlation with J _sc and FF as in FIG. 5C. In addition, both SVA and DPE-added films were cast (19.0

), The lamellae 100 distance of 17.9 mm 3 was further reduced.

Thus, the SVA and DPE additive introduction approach produced thinner laminated lamellar structures with enhanced crystallinity.

In this study, to demonstrate our purpose, we demonstrated a slot die printed large area photovoltaic module consisting of monomolecular BTR using a roll-to-roll compatible DPE-additive method. As described above, the DPE-additive method was found to be sufficient for upscaling fabrication in optimized small single-cell devices.

Here, by using a photovoltaic module consisting of four series-connected with each stripe area 2.5cm ² it provided the total active area of 10 cm ^2.

6 shows the current density-voltage curves of the highest performing printed solar modules and photographic images. Based on this configuration, we were able to obtain a maximum PCE of 4.83% (Voc of 3.76 V, J _sc of 1.84 mA cm ^-2 and FF of 66.0%) and an average PCE of 4.40%. In addition, more preferred processing conditions have been suggested using halogen free solvents and additive systems.

In summary, halogen-free monomolecular solar cells have been successfully manufactured using the scalable slot die coating method. BTR: OS71 based on PC71BM active layer achieved 7.46% PCE with SVA treatment. In addition, halogen-free DPE molecules will be introduced as additives for further application in large area photovoltaic modules.

Photovoltaic results of small active area devices have shown that the DPE additive approach can be effectively used for upscaling single molecule solar cells.

As a result, we demonstrated a monomolecular photovoltaic module with an active area of 10 cm ² , representing 4.83% PCE.

1. Manufacturing Small Scale Solar Cells

The patterned ITO / glass substrates were treated for 15 minutes under UV / O ₃ . PEDOT: PSS (Clevios P VP Al 4083, Heraeus) layer was spin-coated at 5000 rpm for 40 seconds and then heat-treated at 150 ° C for 10 minutes. The active layer was slot die coated from a toluene solution of BTR: PC71BM at a ratio of 1: 1 wt% (15 mg ml ⁻¹ ) at ambient conditions at room temperature.

The coating was carried out using a previously developed 3D printer-based slot die coater with a spacing of 100 μm between the meniscus and the substrate at a coating speed of 12 mm / s.

In addition, according to previous reports, additional N ₂ blower systems were introduced to produce uniform and flawless films. For solvent vapor annealing (SVA) films, THF (1 ml) solution was placed in a 30 mm glass Petri dish and held for 1 minute. The slot die coated film was then attached to the lid of the Petri dish and left for 25 seconds. Meanwhile, the additive introduction film was made from a DPE (0.5 vol%) additive-containing solution.

In this case, further time consuming drying or annealing processes are not necessary.

Finally, all films were completed by thermal evaporation of Ca (20 nm) / Al (80 nm) under a vacuum pressure of 10 ^-7 torr, defining an active area of 10 mm ² .

2. Manufacturing of large area modules

In this study, a large area ITO / glass substrate (8 x 3.3 cm ² ) consisting of patterned stripes (13 nm wide and 2 nm spacing) was used. For module manufacturing, only a roll-to-roll compatible DPE additive approach was implemented. Coating of all layers was carried out according to the method described above (eg preparation of solution). The active area of the module was determined from the overlapped areas of the ITO stripe and the active layer.

As a result, the total active area of the module was calculated to be 10 cm ² , which is the sum of the areas (2.5 cm ² ) of each of the four stripes. In particular, slot die coaters based on 3D printers were suitable for patterning active layers. Thus, we did not use an additional etching process.

3. How to measure

Current density-voltage (JV) characteristics were measured using a Keithley 2400 / Oriel solar simulator (class AAA) under AM 1.5G illumination at an intensity of 100 mW cm ^-2 .

This measurement was calibrated from standard Si solar cells certified by the International System of Units (SI) (SRC 1000 TC KG5 N, VLSI Standards, Inc). External quantum efficiency (EQE) spectra are described by QEX-7 PV Measurements Inc. Obtained using a spectral response system. Ultraviolet-vis spectroscopy (UV-vis) spectroscopy was performed using a Perkin Elmer Lambda 750. The surface morphology of the device was analyzed using a transmission electron microscope (TEM) (Technai G2 S-Twin 3600 KeV electron microscope) and an atomic force microscope (AFM) (Nanoscope, Veeco Instruments, Inc) in tapping mode. Hall and electron mobility were calculated from the space charge limiting current (SCLC) model. In this case, holes-only and electron-only diodes were prepared from devices having the structures of ITO / PEDOT: PSS / BTR: PC71BM / MoO3 / Ag and ITO / ZnO / BTR: PC71BM / Ca / Al, respectively.

The hole and electron mobility were calculated by Mortegney's law. Where ε0 is the free space dielectric constant, εr is the dielectric constant of the mixed film, μ is the hole and electron mobility, V is the voltage drop across the device, and εr is the dielectric constant. J = (9/8) ε ₀ ε _r μ (V ² / L ³ ) L is the thickness of the mixed film. Two-dimensional incident angle wide-angle X-ray scattering (2D GIWAXS) was performed using the 9A U-SAXS beamline of the Pohang Accelerator Laboratory.

Although the embodiments of the present invention have been described above with reference to the accompanying drawings, the present invention is not limited to the above embodiments and can be manufactured in various forms, and having ordinary skill in the art to which the present invention pertains. It will be understood by those skilled in the art that the present invention may be embodied in other specific forms without changing the technical spirit or essential features of the present invention. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive.

Claims (5)

(a) preparing a substrate on which the patterned metal oxide is formed;
(b) forming a conductive polymer layer on the patterned metal oxide substrate;
(c) forming an active layer including a single molecule on the conductive polymer layer;
(d) forming a metal on the active layer to manufacture a monomolecular organic solar cell; And
(e) providing a plurality of solar cells, and connecting a plurality of solar cells in series to manufacture a monomolecular organic solar module.
Step (c) is to coat a solution containing a non-halogen solvent, a non-halogen additive and a single molecule on the conductive polymer layer, to form an active layer comprising a single molecule,
Method for producing a monomolecular organic photovoltaic module.
The method of claim 1,
The metal oxide is a method for producing a monomolecular organic photovoltaic module containing ITO.
The method of claim 1,
The conductive polymer layer is a method for producing a monomolecular organic photovoltaic module comprising PEDOT: PSS.
The method of claim 1,
The single molecule is a method of producing a monomolecular organic photovoltaic module comprising BTR (benzodithiophene terthiophene rhodanine) and [6.6] -phenyl-C71-butyric acid methyl ester (PC71BM).
The method of claim 1,
The non-halogen additive is a method for producing a monomolecular organic photovoltaic module comprising diphenyl ether (DPE).

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