Patent Description:
Copper Indium Gallium Selenium (CIGS) semiconductor thin film has excellent light sensing characteristics not only to visible light, but also to light within the IR to NIR range (<NUM> to <NUM>) in comparison with conventional semiconductor thin films. Therefore, CIGS semiconductor thin film can be used for the production of a broadband photodiode element.

A conventional CIGS photodiode element comprises (<NUM>) a metal electrode thin film layer as anode, (<NUM>) a p-type CIGS semiconductor thin film layer as a light absorbing layer, (<NUM>) an n-type compound semiconductor thin film layer as a buffer layer, (<NUM>) a transparent metal oxide conducting thin film layer as a conducting layer and (<NUM>) a transparent metal oxide thin film layer as cathode (<FIG>).

The metal electrode thin film layer as anode is usually produced by sputter coating using molybdenum.

The p-type CIGS semiconductor thin film layer as a light absorbing layer having high photoelectric conversion characteristics is usually obtained by depositing the CIGS thin film on a substrate coated with the metal electrode thin film layer as anode by vacuum magnetron sputter coating, vacuum co-evaporation coating, printing coating or electroplating coating using binary, trinary or quaternary targets containing elements selected from Cu, In, Ga and Se and processing the same with a selenization treatment. The selenization treatment is the most important step in the conventional process when preparing CIGS. The aim of the selenization treatment is to increase the Se ratio in CIGS, so that the surface bandgap of the element is increased, and thereby addressing the issue that the open-circuit voltage is too low. The selenization treatment is crucial to the grain size and composition of CIGS, and thereby affecting the photoelectric conversion efficiency of CIGS.

The selenization treatment mainly converts a metal precursor to a selenide semiconductor material under a chemical atmosphere of selenium. There are two kinds of common selenization treatments, one is rapid thermal process (RTP) selenization and the other is H<NUM>Se thermal treatment. The RTP uses a solid selenium source for heating, the advantage is the fast reaction, and the drawback is that it is difficult to control the homogeneity of the atmosphere so that the grain size and composition are not adjustable, and thereby the efficiency of the resulted element is low. The H<NUM>Se thermal treatment uses H<NUM>Se for selenization, the advantage is that the atmosphere is controllable so that an element with high efficiency can be obtained, and the drawback is that the batch tube furnace reaction is slow, which causes a long reaction time (<NUM> to <NUM> hours).

The n-type compound semiconductor thin film layer as a buffer layer requires a bandgap matching that of the light absorbing layer, so that a depletion region with sufficient thickness is formed. The buffer layer can prevent the light absorbing layer from being destroyed by the subsequent high energy sputter coating process and can protect the inner crystal structure of the light absorbing layer. The n-type compound semiconductor thin film layer has a direct bandgap and the surface thereof can be doped with Ga or S ions to increase the bandgap, where CdS is frequently used as the material for the n-type compound semiconductor thin film layer. However, considering environmental protection, an n-type compound semiconductor thin film layer which is Cd-free is required.

<CIT> discloses a photosensitive element comprising a p-type CIGS semiconductor thin film layer, an i-type CIGS semiconductor thin film layer and an n-type CIGS semiconductor thin film layer (PIN). The energy bandwidth of an i-type CIGS semiconductor thin film (Eg) is around <NUM> eV and the chemical structure thereof is β-Cu<NUM>(In<NUM>Ga<NUM>)<NUM>Se<NUM>. Accordingly, the preparation of an i-type CIGS semiconductor thin film requires excess amounts of selenium and a high temperature selenization process, i. e, an i-type CIGS semiconductor thin film cannot be prepared simply by sputter coating or evaporation coating. In a PIN photosensitive element, the p-type CIGS semiconductor thin film layer is prepared by the following steps: coating the i-type CIGS semiconductor thin film layer, contacting the same with Cu or Cu alloy electrode, annealing the same at high temperature so that the Cu element of the electrode diffuses to the i-type CIGS semiconductor thin film layer, and thereby the p-type CIGS semiconductor thin film layer is formed. The depth that the Cu element diffuses to the i-type CIGS semiconductor thin film layer is insufficient in such preparation process, so that defects at the interface between the metal electrode and the p-type CIGS semiconductor thin film layer are generated, and thereby proper ohmic contact cannot be formed. Moreover, <CIT> mentions that the i-type CIGS semiconductor thin film layer is for absorbing light, generating electron-hole pairs by the absorbed light and converting the formed current to an electrical signal through the in-built electric field of the PIN structure. However, the i-type CIGS semiconductor thin film layer has many defects in the crystal structure. <CIT> discloses that the thickness of the i-type CIGS semiconductor thin film layer ranges from <NUM> to <NUM> and the thicknesses of the p-type CIGS semiconductor thin film layer and the n-type CIGS semiconductor thin film layer range from <NUM> to <NUM>, and thus there are many defects within the i-type CIGS semiconductor thin film layer. The defects lower the efficiency of forming electron-hole pairs, and the interface between the metal electrode and the p-type CIGS semiconductor thin film layer cannot form proper ohmic contact, and thus the in-built electric field cannot effectively separate the electron-hole pairs and form carrier current. Hence, the CIGS element with PIN structure cannot function effectively. Besides, given that the i-type CIGS semiconductor is thermodynamically unstable, and thereby phase separation occurs during annealing treatment, so it would be difficult to reduce the defects by annealing.

The selenization treatment of the p-type CIGS semiconductor thin film layer and the coating of the n-type compound semiconductor thin film layer using CdS both involve high temperature chemical reactions, so that the inner structure of the films are influenced, and thereby damaging the photoelectric conversion efficiency of the resulting photodiode element. Therefore, a PN junction requiring no selenization treatment and containing no Cd is required, and the PN junction should be suitable to be used in semiconductor thin film elements.

<CIT> and <CIT> each discloses a PN junction, comprising a p-type CIGS semiconductor thin film layer and an n-type CIGS semiconductor thin film layer.

An object of the present invention is to provide a PN junction requiring no selenization treatment and using no Cd buffer layer. The invention provides the PN junction according to claim <NUM> and a process for preparing said junction according to claim <NUM>.

Another object of the present invention is to provide a semiconductor thin film element, in particular a photodiode element, comprising said PN junction. According to one embodiment of the present invention, said photodiode element further comprises a layer containing a molybdenum compound. According to another embodiment of the present invention, said photodiode element further comprises a light converting thin film layer emitting light having a wavelength within the range of <NUM> to <NUM>. According to another embodiment of the present invention, said photodiode element further comprises both a layer containing a molybdenum compound and a light converting thin film layer emitting light within the range of <NUM> to <NUM>.

Another object of the present invention is to provide a photoelectric sensing module comprising said semiconductor thin film element, in particular a photodiode element, comprising said PN junction.

Another object of the present invention is to provide a use of said photoelectric sensing module, for biometrics, an IR imaging night vision system, an NIR photoelectric switch or an X-ray camera.

The additional characteristics and advantages of the present inventions will be partially disclosed in the following sections or illustrated by the working examples of the subject application.

The following text will briefly describe drawings necessary for describing the working examples of the subject application or for describing the prior art so that the working examples of the subject application are more comprehensible. Obviously, the drawings described in the following text are only a part of the working examples of the subject application, and a person of ordinary skill in the art can deduce other working examples in view of the structures illustrated in the drawings of the subject application without difficulty.

The working examples of the subject application will be described in detail in the following text. Common reference numerals are used throughout the drawings and the detailed description section to indicate the same or similar components. The working examples concerning the drawings described herein are for explanation and/or illustration and for providing a better understanding of the subject application. The working examples of the subject application shall not be interpreted as limitations to the subject application.

In order to facilitate understanding of the disclosure herein, terms are hereby defined below.

The term "about" refers to an acceptable deviation of a given value measured by a person of ordinary skill in the art, depending, in part, on how to measure or determine the value.

Unless otherwise stated herein, the terms "a/an," "the" and the like used in the description, especially in the appended claims, should be understood to include both singular and plural forms. All the working examples and exemplary terms ("for example" and "such as") are for giving examples of the present invention rather than limiting the scope of the present invention.

In specific embodiments and claims of the present application, a list of items joined by the term "one of" may mean any one of the listed items. For example, if items A and B are listed, then the phrase "one of A and B" means only A or only B. In another example, if items A, B, and C are listed, then the phrase "one of A, B and C" means only A; only B; or only C. The item A may comprise a single component or multiple components. The item B may comprise a single component or multiple components. The item C may comprise a single component or multiple components.

In specific embodiments and claims of the present application, a list of items connected by the term "at least one of" may mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B and C are listed, then the phrase "at least one of A, B and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B and C. The item A may comprise a single component or multiple components. The item B may comprise a single component or multiple components. The item C may comprise a single component or multiple components.

The present invention will be described in detail as follows.

The PN junction of the present invention comprises the following semiconductor thin film layers:.

Said PN junction (<FIG>) replaces the n-type compound semiconductor thin film layer according to the prior art with an n-type CIGS semiconductor thin film layer in order to eliminate the selenization treatment and to decrease the high processing temperature in the process according to the prior art.

The p-type CIGS semiconductor thin film layer used in the present invention has a Cu to In molar ratio within the range of <NUM> to <NUM>. For example, the p-type CIGS semiconductor thin film layer may have a Cu to In molar ratio of, but is not limited to, <NUM>, <NUM>, <NUM>, <NUM> or <NUM>, preferably <NUM>, more preferably <NUM>. If said molar ratio is more than <NUM>, many CuIn acceptor defects will form in the crystal structure within the film layer, and thereby affect the light absorbing efficiency and the hole carrier transportation. If said molar ratio is less than <NUM>, the p-type CIGS semiconductor cannot be produced. Using p-type CIGS semiconductor with said molar ratio has less defects in the crystal structure and has a higher light absorbing coefficient and a better hole carrier transportation.

According to an embodiment of the present invention, said p-type CIGS semiconductor material has a chemical formula of Cu(InxGa<NUM>-x)Se<NUM>, where the x in the chemical formula may be, but is not limited to, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>.

The n-type CIGS semiconductor thin film layer used in the present invention has a Cu to In molar ratio within the range of <NUM> to <NUM>. For example, the n-type CIGS semiconductor thin film layer may have a Cu to In molar ratio of, but is not limited to, <NUM>, <NUM>, <NUM>. If said molar ratio is more than <NUM>, the N-type CIGS semiconductor thin film layer cannot be produced. If the molar ratio is less than <NUM>, many Incu donor defects will form in the crystal structure within the film layer, and thereby affect the electron carrier transportation. Using n-type CIGS semiconductor with said molar ratio requires no selenization treatment. According to an embodiment of the present invention, said n-type CIGS semiconductor material has a chemical formula of Cu(InxGa<NUM>-x)Se<NUM>, where the x in the chemical formula may be, but is not limited to <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or <NUM>.

The PN junction according to the present invention can be used in a semiconductor thin film element; for example, it can be, but is not limited to, a semiconductor transistor element or photodiode element, in particular a photodiode element.

The semiconductor thin film photodiode element according to the present invention comprises the following thin film layers (<FIG>):.

Said semiconductor thin film photodiode element requires no selenization treatment and uses no CdS n-type compound semiconductor layer in its preparation process, and thus does not involve high temperature reactions. Said semiconductor thin film photodiode element can be prepared at a temperature in the range of about <NUM> to <NUM>, and thus the influence on the crystal structure within the thin film can be avoided. Said semiconductor thin film photodiode element has higher photoelectric conversion efficiency.

Said metal electrode thin film layer as anode has no special limitations. It can be any metal electrode material known to a person of ordinary skill in the art. For example, it can be, but is not limited to, materials comprising Mo, such as, but without being limited to, Mo, Ti/Mo, Cr/Mo, Al/Mo, Au/Mo or materials containing Ti, Au, Ag, Cu or Cr.

Said PN junction is the PN junction according to the present invention, comprising a p-type CIGS semiconductor thin film layer as a light absorbing layer and an n-type CIGS semiconductor thin film layer as a buffer layer. Said p-type CIGS semiconductor thin film layer as a light absorbing layer has photoelectric conversion characteristics, has a high light absorbing coefficient (larger than <NUM>-<NUM>), and can absorb light with a wavelength in the range of <NUM> to <NUM>, preferably in the range of <NUM> to <NUM>, more preferably in the range of <NUM> to <NUM>. The bandgap of said n-type CIGS semiconductor thin film layer as a buffer layer matches that of the light absorbing layer so that a depletion region with sufficient thickness is formed, and the buffer layer can prevent the light absorbing layer from being destroyed by the subsequent high energy sputter coating process and can protect the inner crystal structure of the light absorbing layer.

Said transparent metal oxide conducting thin film layer as a conducting layer has no special limitations. It can be any metal electrode material known to a person of ordinary skill in the art. For example, it can be, but is not limited to, i-ZnO/ITO, i-ZnO/AZO, i-ZnO/BZO (ZnO:B), i-ZnO/IWO (In<NUM>O<NUM>:W), i-ZnO/IWZO (In<NUM>O<NUM>:W:ZnO).

Said transparent metal oxide thin film layer as cathode has no special limitations. It can be any metal electrode material known to a person of ordinary skill in the art. For example, it can be, but is not limited to, i-ZnO/ITO, i-ZnO/AZO, i-ZnO/BZO (ZnO:B), i-ZnO/IWO (In<NUM>O<NUM>:W), i-ZnO/IWZO (In<NUM>O<NUM>:W:ZnO).

The material of said transparent metal oxide conducting thin film layer as a conducting layer can be the same as or different from that of said transparent metal oxide thin film layer as cathode.

According to an embodiment of the present invention, said semiconductor thin film photodiode element further comprises a layer containing a molybdenum compound as a hole transportation thin film layer. Said hole transportation thin film layer is preferably between said metal electrode thin film layer as anode and the p-type CIGS semiconductor thin film layer of said PN junction (<FIG>), so that the potential difference between the Mo anode thin film layer and the p-type CIGS semiconductor thin film layer is reduced, and thereby the efficiency with which the hole is transported to the anode is increased. Said hole transportation thin film layer is a layer containing a molybdenum compound, and the material thereof can be, for example, but is not limited to, MoO<NUM>, MoSe<NUM> or molybdenum compounds doped with a small amount of at least one of elements Li, Na, K, Rb and Cs.

In preparing CIGS photodiode elements, soda-lime glass substrates are frequently used because the alkaline metal ions in the soda-lime glass substrates can diffuse into the CIGS semiconductor thin film layer under high temperature processes, and thereby improve the electric properties of the semiconductor thin film layer. Said hole transportation thin film layer is suitable to be applied to soda-lime glass substrates. On the other hand, when preparing thin film transistor elements, non-soda-lime glass substrates are frequently used in order to avoid the alkaline metal ions in the soda-lime glass substrates diffusing into the oxide layer within the thin film transistor element under high temperature processes, thereby decreasing the electric properties of the thin film transistor elements. It is known that said hole transportation thin film layer can be applied to soda-lime glass substrates, and the photoelectric conversion efficiency will not be altered when said hole transportation thin film layer is applied to the non-soda-lime glass substrates.

According to another embodiment of the present invention, said semiconductor thin film photodiode element further comprises a light converting thin film layer (<FIG>). Said light converting thin film layer is mainly for absorbing incident light of different wavelengths and converting the same to light that can be easily absorbed by the p-type CIGS semiconductor thin film layer as a light absorbing layer, for example, but not being limited to, light of wavelength in the range of <NUM> to <NUM>, preferably <NUM> to <NUM>, more preferably <NUM> to <NUM>, and thereby increasing the light absorption of the p-type CIGS thin film layer and promoting the photoelectric conversion of the photodiode element. Said light converting thin film layer may be coated or glued onto the photodiode element and may have a thickness in the range of <NUM> to <NUM>, preferably in the range of <NUM> to <NUM>. Said light converting thin film layer also has a function of preventing the cathode/transparent metal oxide conducting thin film layer from being chemically corroded by moisture or acidic or basic liquid, thereby increasing the lifetime of the photodiode element.

Said light converting thin film layer has no special limitations. It can be any light emitting material known to a person of ordinary skill in the art. For example, it can be, but is not limited to, light emitting materials selected from the group consisting of quantum dots, organic phosphorescent or fluorescent materials and rare earths.

According to another embodiment of the present invention, said semiconductor thin film photodiode element comprises both a layer containing a molybdenum compound as hole transportation thin film layer and a light converting thin film layer (<FIG>). Said light converting thin film layer may be coated or glued onto the photodiode element and may have a thickness in the range of <NUM> to <NUM>, preferably in the range of <NUM> to <NUM>.

The photoelectric sensing module according to the present invention comprises a semiconductor thin film element comprising a PN junction according to the present invention.

According to an embodiment of the present invention, said semiconductor thin film element is a semiconductor thin film photodiode element, and the photoelectric sensing module further comprises a semiconductor thin film transistor element and a semiconductor light emitting element.

According to an embodiment of the present invention, said semiconductor thin film photodiode element, said semiconductor thin film transistor element and said semiconductor light emitting element are integrated on the same substrate.

According to an embodiment of the present invention, said substrate can be, for example, but is not limited to, glass substrate, stainless steel substrate or flexible substrate, for example, but without being limited to, a plastic thin film substrate.

According to an embodiment of the present invention, the material of the metal electrode thin film layer as anode in said semiconductor thin film photodiode element and the material of source drain electrodes in said semiconductor thin film transistor element are the same molybdenum compound, so they can be prepared at the same time.

According to an embodiment of the present invention, said semiconductor light emitting element can be, for example, but not being limited to, an X-ray, UV LED, IR LED, IR LD or RGB OLED light source.

The photoelectric sensing module according to the present invention can be used for biometrics, an IR imaging night vision system, an NIR photoelectric switch or an X-ray camera.

The subject application provides a process for preparing said PN junction, comprising the following steps:.

wherein there are two, three or four targets in the coating chambers.

Said target material can be binary, trinary or quaternary targets containing elements selected from Cu, In, Ga and Se, preferably a binary, trinary or quaternary target, for example, but not being limited to, a binary target containing Ga and Se, such as GaxSey, <NUM><x<<NUM>, <NUM><y<<NUM>, for example, Ga<NUM>Se<NUM>, Ga<NUM>Se<NUM>, or Ga<NUM>Se<NUM>, or containing In and Se, such as InxSey, <NUM><x<<NUM>, <NUM><y<<NUM>, for example In<NUM>Se<NUM>, In<NUM>Se<NUM>, or In<NUM>Se<NUM>, containing Cu and Se, such as CuxSey, <NUM><x<<NUM>, <NUM><y<<NUM>, for example, Cu<NUM>Se<NUM>, Cu<NUM>Se<NUM>, or Cu<NUM>Se<NUM>, a trinary target containing Cu, Ga and Se, Cu, In and Se, or Cu, In and Ga, or a quaternary target containing Cu, In, Ga and Se, such as, but not being limited to, CuyGaSez, Cuy(InxGa<NUM>-x)Sez , wherein <NUM>≤x≤<NUM>, for example, but is not limited to <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or <NUM> ;.

The combination of the targets used for the preparation of CIGS may be, for example but without being limited to, a combination of a binary target material and a trinary target material; a combination of a binary target material and a quaternary target material; a combination of two binary target materials; a combination of three binary target materials; or a combination of two trinary target materials, etc. A person of ordinary skill in the art would know how to choose the combination of the targets, i.e., including all four elements Cu, In, Ga and Se in the chosen combination.

Said annealing uses a green light laser or an electric heater as a heating source, wherein said process is a dry process and requires no selenization treatment.

Said inert gas has no special limitations. It can be any inert gas known to a person of ordinary skill in the art. For example, it can be, but is not limited to, nitrogen or argon.

Said annealing can be rapid annealing which is not a selenization treatment and does not involve a substance containing selenium. Said heating source can be, for example, but is not limited to, a green light laser or an electric heater.

According to an embodiment of the present invention, when a green light laser is used as a heating source, the annealing time is in the range of <NUM> to <NUM> seconds.

According to an embodiment of the present invention, when an electric heater is used as a heating source, the annealing time is in the range of <NUM> to <NUM> seconds.

According to an embodiment of the present invention, the PN junction is prepared on a flexible substrate.

In one embodiment, said semiconductor thin film photodiode element is prepared by vacuum magnetron sputter coating. When a light converting thin film layer is present, the light converting thin film layer is prepared by jet printing coating, screen printing coating, spin coating, slit nozzle coating, thermal copying coating or transfer printing.

During the preparation of said photodiode element, the thin film layer of the thin film transistor element and the metal wire already prepared on the substrate are not chemically reacted or thermally aged because the temperature is controlled to be within <NUM> and no selenization treatment is required. Said process for preparing photodiode element eliminates preparation steps and the functions of the photodiode element and the thin film transistor element integrated on the same substrate are not altered.

EXAMPLES Embodiments of the PN junction according to the present invention have Cu to In molar ratio for the p-type CIGS layer and for the n-type CIGS layer falling within the ranges recited in claim <NUM>.

The process for preparing the PN junction comprises the following steps:.

The n-type CIGS semiconductor thin film layers of the working examples are prepared by using the following targets:.

The process for preparing a semiconductor thin film photodiode element comprising the PN junction according to the present invention comprises the following steps:.

Accordingly, semiconductor thin film photodiode elements are obtained with a layer order: glass substrate/ Mo (<NUM>)/Mo:Na (<NUM>)/p-type CIGS (<NUM>)/n-type CIGS (<NUM>)/i-ZnO (<NUM>)/ITO (<NUM>). When said photodiode element according to the working examples of the present invention are applied to a solar cell, the short circuit current density (Jsc), the open circuit voltage (Voc), the fill factor (FF) and the conversion efficiency (EFF) are present in Table <NUM>.

Table <NUM> provides a comparison between the photodiode element according to the working examples of the subject application and photodiode elements provided in references.

Comparative example <NUM>: Inline Cu(In,Ga)Se<NUM> co-evaporation for high-efficiency solar cells and modules (<NPL>).

Comparative example <NUM>: Surface modification of CIGS film by annealing and its effect on the band structure and photovoltaic properties of CIGS solar cells (<NPL>).

Comparative example <NUM>: Study of thin film solar cells in high temperature condition (<NPL>).

Comparative example <NUM>: Deposition technologies of high-efficiency CIGS solar cells: development of two-step and co-evaporation processes (<NPL>).

Comparative example <NUM>: soda-lime glasses/Mo(about <NUM>±<NUM>)/ClGS(<NUM>±<NUM>)/CdS(<NUM>)/i-ZnO(<NUM>±<NUM>)/ ZnO:Al(<NUM>±<NUM>)/ MgF<NUM>(<NUM>±<NUM>).

Comparative example <NUM>: soda-lime glasses/Mo/CIGS(<NUM>)/CdS(<NUM>)/ i-ZnO(<NUM>)/ZnO:Al(<NUM>).

Comparative example <NUM>: soda-lime glasses/Mo/CIGS(<NUM>)/CdS(<NUM>)/ ZnO(<NUM>) Comparative example <NUM>: soda-lime glasses/Mo(about <NUM>)/CIGS(about <NUM>)/CdS(about <NUM>)/ i-ZnO(about <NUM>)/ ZnO:Al(<NUM>).

Comparative examples <NUM> to <NUM> all involve an n-type semiconductor thin film layer containing CdS. It is notable that the photodiode elements according to the present invention are produced by a dry process and require no selenization treatment. The photodiode elements according to the present invention are environmentally friendly given that they are prepared by a Cd free process. Under such circumstance, the efficiency (<NUM>%) decreases maxima <NUM>% in comparison with the prior art (<NUM>% <IMG> <NUM>%), and even increases at least <NUM>% in comparison with comparative example <NUM>.

Claim 1:
A PN junction, comprising a p-type CIGS semiconductor thin film layer and an n-type CIGS semiconductor thin film layer, characterised in that the Cu to In molar ratio in the p-type CIGS semiconductor thin film layer is within a range of <NUM> to <NUM>, and wherein the Cu to In molar ratio in the n-type CIGS semiconductor thin film layer is within a range of <NUM> to <NUM>.