JP2011155276A - Organic photoelectric conversion element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic photoelectric conversion element that efficiently reads signal charges out, and suppresses generation of a residual image. <P>SOLUTION: The organic photoelectric conversion element 10, having an organic photoelectric conversion film photoelectrically converting incident light to generate signal charges, includes a first electrode provided on one surface of the organic photoelectric conversion film 101 and a plurality of second electrodes arrayed on the other surface of the organic photoelectric conversion film 101, a gap between adjacent second electrodes being ≤3 μm. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an organic photoelectric conversion element including an organic photoelectric conversion film that photoelectrically converts incident light and generates a signal charge.

  Conventionally, single-plate image sensors represented by CCD image sensors and CMOS image sensors correspond to each color filter by providing three or four types of mosaic color filters on a pixel (photodiode) array for photoelectric conversion. A color signal is output. Then, the output color signal is signal-processed to generate a color image. However, an image sensor provided with a mosaic color filter has the disadvantages that, in the case of a primary color filter, approximately 2/3 of incident light is absorbed by the color filter, so that the light use efficiency is poor and the sensitivity is low. Also, since only one color signal can be obtained for each pixel, the resolution is also poor. In particular, false colors are conspicuous.

  In order to overcome such drawbacks, conventionally, for example, an image sensor as disclosed in Patent Document 1 below has been developed. In this image sensor, by providing triple wells (photodiodes) for optical signal detection in the silicon substrate, signals with different spectral sensitivities (wavelengths of blue, green and red from the surface) due to differences in the depth of the silicon substrate. With a peak). Although the resolution is good and the light use efficiency is improved, the spectral sensitivity characteristics of the RGB output signal are not sufficiently separated, so the color reproducibility is poor and the output signal is adjusted to obtain a true RGB signal. This addition / subtraction has the disadvantage that the S / N deteriorates. Therefore, as in Patent Documents 2 and 3, an image sensor that improves separation of spectral sensitivity characteristics of RGB output signals has been researched and developed. These image sensors are image sensors with a three-layer photoelectric conversion film structure, for example, a pixel structure in which photoelectric conversion films that sequentially generate signal charges for B, G, and R light from the light incident surface are stacked. For each pixel, a readout unit that can independently read out signal charges generated by the photoelectric conversion films is provided in an integrated manner. Therefore, in the case of this image sensor, incident light is photoelectrically converted and read out, so that the use efficiency of visible light is close to 100%, and color signals of three colors R, G, and B are obtained in each pixel. Furthermore, since the spectral sensitivity characteristics of the three-layer photoelectric conversion film can be selected independently, the spectral sensitivity characteristics of the RGB output signals are well separated. Therefore, it is possible to obtain an image with high sensitivity, high resolution (false color is not conspicuous), color reproduction, and good S / N.

JP-T-2002-513145 Special Table 2002-502120 JP 2002-83946 A

  By the way, in the solid-state imaging device using the organic photoelectric conversion film described in Patent Documents 2 and 3, a pixel electrode divided for each pixel is constructed, and an organic photoelectric conversion film and a counter electrode are shared on all pixels. Laminate with. In this case, the gap (gap) between adjacent pixel electrodes has a smaller electric field strength than that on the pixel electrode, so that it takes time to read out signal charges generated in the gap, resulting in an afterimage. there were.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an organic photoelectric conversion element that can efficiently read out signal charges and suppress the occurrence of afterimages.

  As a result of intensive studies, the present inventor has found that the occurrence of an afterimage can be suppressed to a level that does not cause a problem in practice by setting the gap between the pixel electrodes to a predetermined dimension or less. That is, the above object of the present invention is achieved by the following configuration.

(1) An organic photoelectric conversion element including an organic photoelectric conversion film that photoelectrically converts incident light and generates a signal charge,
A first electrode provided on one surface of the organic photoelectric conversion film;
A plurality of second electrodes arranged on the other surface of the organic photoelectric conversion film,
The organic photoelectric conversion element characterized by the clearance gap between adjacent 2nd electrodes being 3 micrometers or less.
(2) The organic photoelectric conversion element as described in (1) above, wherein the first electrode is composed of a single counter electrode having optical transparency.
(3) The organic photoelectric conversion element as described in (1) or (2) above, wherein the plurality of second electrodes are pixel electrodes arranged for each pixel region.
(4) The organic photoelectric conversion element according to any one of (1) to (3), wherein the second electrode is connected to a readout circuit that reads out signal charges and transfers them to an output unit. .

  ADVANTAGE OF THE INVENTION According to this invention, the signal charge can be read efficiently and the organic photoelectric conversion element which can suppress generation | occurrence | production of an afterimage can be provided.

It is sectional drawing which shows schematic structure of an organic photoelectric conversion element. It is a top view which shows arrangement | positioning of a pixel electrode. It is a graph which shows the generation | occurrence | production ratio of the afterimage at the time of light extinction of an organic photoelectric conversion element at the time of using merocyanine for the photoelectric conversion material which comprises an organic photoelectric conversion film. It is a graph which shows the generation | occurrence | production ratio of the afterimage after 1 frame at the time of changing the clearance gap (Gap) of the organic photoelectric conversion element of FIG. It is a graph which shows the generation | occurrence | production ratio of the afterimage of an organic photoelectric conversion element at the time of using a phthalocyanine for the photoelectric conversion material which comprises an organic photoelectric conversion film. It is a graph which shows the ratio of generation | occurrence | production of the afterimage of 1 frame at the time of changing the clearance gap (Gap) of the organic photoelectric conversion element of FIG. It is a graph which shows the generation | occurrence | production ratio of the afterimage of an organic photoelectric conversion element at the time of using 4H pyran for the photoelectric conversion material which comprises an organic photoelectric conversion film. It is a graph which shows the ratio of generation | occurrence | production of the afterimage of 1 frame at the time of changing the clearance gap (Gap) of the organic photoelectric conversion element of FIG. It is a graph which shows the correlation of the ratio of the generation of the afterimage with respect to the number of frames when the electrode area of the pixel electrode is changed. It is a graph which shows the correlation of the ratio of afterimage generation with respect to the number of frames when the voltage of the counter electrode is changed.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a cross-sectional view illustrating a schematic configuration of the organic photoelectric conversion element of the present embodiment. FIG. 2 is a plan view showing the arrangement of the pixel electrodes. As shown in FIG. 1, the organic photoelectric conversion element 10 includes an organic photoelectric conversion film 101 that photoelectrically converts incident light and generates signal charges. A counter electrode 102 is provided on one surface of the organic photoelectric conversion film 101, and a plurality of pixel electrodes 100 are provided on the other surface. In the present embodiment, incident light is irradiated from the upper side of the organic photoelectric conversion film 101 in the drawing, and the signal charge generated by the organic photoelectric conversion film 101 is changed from the lower side of the organic photoelectric conversion film 101 in the drawing. This is a configuration to be read out. The pixel electrode 100 and the counter electrode 102 are not particularly limited as long as an electric field can be generated in the organic photoelectric conversion film 101 during imaging. The first electrode is provided on one surface of the organic photoelectric conversion film 101, and the other A plurality of second electrodes arranged on the surface can be provided.

  A pixel is constituted by three layers of the counter electrode 102, the organic photoelectric conversion film 101, and one pixel electrode 100.

  The counter electrode 102 is made of a light transmissive electrode material, has a film shape common to all pixel regions, and is made of a single member. The counter electrode 102 is electrically connected to a voltage supply means (not shown), and a voltage is applied and set to the potential V2 during imaging. The counter electrode 102 is made of a material that is optically transparent or has little light absorption. For example, the counter electrode 102 is made of a metal compound such as ITO or a very thin metal film.

  The pixel electrode 100 is formed by separating the pixel electrodes 100 for each pixel at a predetermined interval on a two-dimensional plane parallel to the counter electrode 102. The pixel electrode 100 is made of a conductive material such as a metal or a metal compound. As shown in FIG. 2, each pixel electrode 100 has a substantially square shape in plan view. Note that a taper may be formed at the peripheral edge of each pixel electrode 100 as necessary.

  The organic photoelectric conversion film 101 is made of an organic material that generates a signal charge corresponding to incident light by photoelectric conversion when irradiated with light. The organic photoelectric conversion film 101 may be formed with a blocking layer or a transport layer that prevents passage of holes and electrons as necessary. As the organic photoelectric conversion film 101, a material having intrinsic spectral sensitivity such as merocyanine, phthalocyanine, 4H pyran, quinacridone, or the like is used. In this embodiment, the organic photoelectric conversion film 101 is formed in a single film shape in common for all pixels.

  As the signal charge, either electron / hole (hole) may be used. It is desirable to use a carrier with high mobility. In the present embodiment, holes are used as signal charges.

  Each pixel electrode 100 is electrically connected by a wiring layer, a plug, or the like to a readout circuit that reads out a signal charge and transfers the signal charge to an output unit during charge readout. The readout circuit can be configured to include a MOS transistor on a semiconductor substrate. Further, the readout circuit may be any of a charge transfer / output system using a charge coupled device, a current output system using a thin film transistor, and the like. The organic photoelectric conversion element according to the present invention can obtain the effects described later regardless of the configuration of the readout circuit.

  In this embodiment, as shown in FIGS. 1 and 2, the gap between adjacent pixel electrodes 100 is a, and the width of the pixel electrode 100 (in the case of a square electrode as in this embodiment, the periphery thereof) D), the arrangement pitch of the pixel electrodes 100 is p, and the thickness of the organic photoelectric conversion film 101 is t. In addition, the electric field on the pixel electrode 100 in the organic photoelectric conversion film 101 was E, and the electric field in the gap between the pixel electrodes 100 was E ′. Furthermore, the mobility of the signal charge of the organic photoelectric conversion film 101 is u. The electric fields E and E ′ can be expressed by the following equations, respectively.

  In general, the time τ required for carrier movement in the organic photoelectric conversion film 101 is expressed by the following equation using the carrier mobility u in the organic photoelectric conversion film 101. Here, l represents the moving distance, and E represents the electric field strength.

  Accordingly, the time T1 required for carriers generated near the counter electrode immediately above the pixel electrode 100 to reach the pixel electrode is expressed by the following equation.

  On the other hand, the time T2 required for the signal charge generated on the outermost surface of the organic photoelectric conversion film 101 at the center of the gap (where the electric field strength is weakest) to reach the pixel electrode 100 is expressed by the following equation.

  In order to prevent the afterimage from occurring, both T1 and T2 need to be shorter than one frame period T. From T1 <T2, if the relationship of T2 <T is satisfied, no afterimage is generated.

When T = 33 msec., V2−V1 = 10 V, and the organic photoelectric conversion film 101 has a mobility u = 1x10 ⁻⁶ cm ² / V · sec, t = 200 nm, if a <10 μm is satisfied, the afterimage is theoretically Will not occur.

  However, according to the research of the present inventor, when the organic photoelectric conversion element 10 is actually made, a result like the above-mentioned theory cannot be obtained, and an afterimage is still generated unless the gap a is further reduced. I understood. As one of the factors, it can be considered that the behavior of carriers in the organic photoelectric conversion film 101 exhibits a behavior that cannot be expressed by the above formula.

Therefore, the present inventor conducted the following experiment in order to confirm how much an afterimage is generated in the organic photoelectric conversion element when each configuration is changed.
FIG. 3 is a graph showing the ratio of occurrence of afterimages when the organic photoelectric conversion element is turned off when merocyanine is used as the photoelectric conversion material constituting the organic photoelectric conversion film. FIG. 4 is a graph showing a ratio of afterimage generation after one frame when the gap (Gap) of the organic photoelectric conversion element in FIG. 3 is changed. FIG. 5 is a graph showing a ratio of occurrence of an afterimage of the organic photoelectric conversion element when phthalocyanine is used as the photoelectric conversion material constituting the organic photoelectric conversion film. FIG. 6 is a graph showing a ratio of afterimage generation after one frame when the gap (Gap) of the organic photoelectric conversion element in FIG. 5 is changed. FIG. 7 is a graph showing the ratio of occurrence of afterimages of organic photoelectric conversion elements when 4H pyran is used as the photoelectric conversion material constituting the organic photoelectric conversion film. FIG. 8 is a graph showing the ratio of afterimage generation after one frame when the gap (Gap) of the organic photoelectric conversion element in FIG. 7 is changed. In the graphs shown in FIGS. 3, 5, and 7, the vertical axis indicates the ratio of occurrence of afterimages to the number of frames (Sig.%), And the horizontal axis indicates the number of frames. Here, when measuring each photoelectric conversion element, the light source was turned off in synchronization with the 0th frame. In the graphs shown in FIGS. 4, 6, and 8, the vertical axis represents the afterimage generation ratio (Sig.%) After one frame, and the horizontal axis represents the gap size (μm).

  In the organic photoelectric conversion element shown in FIG. 3, the gaps between the pixel electrodes were changed to 5 μm, 4 μm, 3 μm, and 2 μm, and the degree of occurrence of afterimages was compared. Then, when the gap was 5 μm and 4 μm, afterimages were observed in 1 to 3 frames. However, when the gap was 3 μm and 2 μm, the afterimages had no practical problem regardless of the number of frames. It was found that the level could be suppressed.

  In addition, as shown in FIG. 4, it was found that when the gap is 3 μm or less, the afterimage after one frame can be suppressed to almost zero.

  In the organic photoelectric conversion element shown in FIG. 5, the gaps between the pixel electrodes were changed to 6 μm, 4.5 μm, 3 μm, and 1.5 μm, and the degree of occurrence of afterimages was compared. Then, when the gap was 6 μm and 4.5 μm, an afterimage was observed in 1 to 4 frames, but when the gap was 3 μm and 1.5 μm, the afterimage was practical regardless of the number of frames. It turned out that it was able to be suppressed to the level without a problem above.

  Further, as shown in FIG. 6, it was found that when the gap is 3 μm or less, the afterimage after one frame can be suppressed to almost zero.

  In the organic photoelectric conversion element shown in FIG. 7, the gaps between the pixel electrodes were changed to 5.5 μm, 4 μm, 3 μm, and 2.5 μm, and the degree of occurrence of afterimages was compared. Then, when the gap was 5 μm and 4 μm, an afterimage was observed in 1 to 4 frames. However, when the gap was 3 μm and 2.5 μm, the afterimage was a practical problem regardless of the number of frames. It turned out that it was able to be suppressed to the level without.

  In addition, as shown in FIG. 8, it was found that when the gap is 3 μm or less, the occurrence of afterimage after one frame can be suppressed to almost zero.

  Thus, in the configuration using each photoelectric conversion material (merocyanine, phthalocyanine, 4H pyran) for the organic photoelectric conversion film, an afterimage becomes a problem when the gap between the pixel electrodes is 3 μm or less regardless of the photoelectric conversion material. It was found that the afterimage appeared significantly when the gap was 4 μm or more.

Next, an afterimage with respect to the frame was measured when the area of the pixel electrode and the voltage applied to the counter electrode were changed. In this measurement, merocyanine was used as a photoelectric conversion material.
FIG. 9 is a graph showing the correlation of the ratio of afterimage generation to the number of frames when the electrode area of the pixel electrode is changed. Here, each correlation was measured in a configuration in which the electrode area was 5 μm × 5 μm, 10 μm × 10 μm, and 15 μm × 15 μm. In this measurement, the gap between the pixel electrodes was 3 μm, and the voltage applied to the counter electrode was 10V. As a result, when the gap between the pixel electrodes was 3 μm, it was possible to suppress the occurrence of afterimages for each number of frames regardless of the electrode area.

  FIG. 10 is a graph showing the correlation of the ratio of afterimage generation to the number of frames when the counter electrode voltage is changed. Here, each correlation was measured in a configuration in which the voltage (V2) of the counter electrode was 5V, 7V, and 10V. In this measurement, the gap between the pixel electrodes was 3 μm, and the electrode area of the pixel electrode was 10 μm × 10 μm. As a result, when the gap between the pixel electrodes was 3 μm, it was possible to suppress the occurrence of afterimages for each number of frames regardless of the voltage of the counter electrode.

  When the above measurement was verified, it was found that the organic photoelectric conversion element has an influence on the afterimage due to the gap between the pixel electrodes without depending on the electrode area of the pixel electrode or the voltage of the counter electrode. That is, by setting the gap between the pixel electrodes to 3 μm or less, it is possible to suppress the occurrence of an afterimage regardless of the electrode area of the pixel electrode and the voltage of the counter electrode.

  Since the organic photoelectric conversion element according to the present invention has a configuration in which the gap between the pixel electrodes is 3 μm or less, generation of an afterimage can be suppressed, and the signal charge generated by the organic photoelectric conversion film is in the film. The signal charge can be efficiently read out by suppressing the remaining in the signal.

DESCRIPTION OF SYMBOLS 10 Organic photoelectric conversion element 100 Pixel electrode 101 Organic photoelectric conversion film 102 Opposite electrode a (between pixel electrodes) gap

Claims (4)

An organic photoelectric conversion element including an organic photoelectric conversion film that photoelectrically converts incident light and generates a signal charge,
A first electrode provided on one surface of the organic photoelectric conversion film;
A plurality of second electrodes arranged on the other surface of the organic photoelectric conversion film,
The organic photoelectric conversion element characterized by the clearance gap between adjacent 2nd electrodes being 3 micrometers or less.   The organic photoelectric conversion element according to claim 1, wherein the first electrode is composed of a single counter electrode having light transmittance.   The organic photoelectric conversion element according to claim 1, wherein the plurality of second electrodes are pixel electrodes arranged for each pixel region.   4. The organic photoelectric conversion element according to claim 1, wherein the second electrode is connected to a readout circuit that reads out a signal charge and transfers the signal charge to an output unit. 5.

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