Photoelectric conversion device and method of making the same

Abstract

A photoelectric conversion device has a non-single-crystal semiconductor laminate member formed on a substrate having a conductive surface, and a conductive layer formed on the non-single-crystal semiconductor laminate member. The non-single-crystal semiconductor laminate member has such a structure that a first non-single-crystal semiconductor layer having a P or N first conductivity type, an I-type second non-single-crystal semiconductor layer and a third non-single-crystal semiconductor layer having a second conductivity type opposite the first conductivity type are laminated in this order. The first (or third) non-single-crystal semiconductor layer is disposed on the side on which light is incident, and is P-type. The I-type non-single-crystal semiconductor layer has introduced thereinto a P-type impurity, such as boron which is distributed so that its concentration decreases towards the third (or first) non-single-crystal semiconductor layer in the thickwise direction of the I-type layer.

Description

abovesaid above said CVD method. In this case, the semiconductor raw material gas is one that is obtained by passing a semiconductor raw material gas through a molecular sieve or zeolite which adsorbs oxygen, and/or carbon and/or phosphorus. Accordingly, the non-single-crystal semiconductor layer 5 is formed to contain oxygen at a concentration less than 5×10¹⁹ atoms/cm³ as low as 5×10¹⁸ atoms/cm³, and/or carbon at a concentration level less than 4×10¹⁹ 4×10¹⁸ atoms/cm³ as low as 4×10¹⁵ atoms/cm³, and/or phosphorus at a concentration at least as low as 5×10¹⁵ atoms/cm³.

The non-single-crystal semiconductor layer 6 is formed of, for instance, microcrystalline silicon, and has a thickness of, for example, 100 to 300 angstroms. Moreover, the energy band gap of layer 6 is preferably larger than that of layer 5.

The non-single-crystal semiconductor layer 6 is formed by a CVD method which employs a semiconductor raw material gas composed of a hydride or halide of silicon, for example, Si_nH_2n+2 (where n is greater than or equal to 1) or SiF_m (where m is greater than or equal to 2), and an impurity material gas composed of a hydride or halide of an N-type impurity, for instance, phosphine (PH₃), the CVD method may or may not employ a glow discharge (plasma) or light. In this case, the non-single-crystal semiconductor layer 6 has an N-type impurity (phosphorus) introduced thereinto with a concentration of 1×10¹⁹ to 6×10²⁰ atoms/cm³, as shown in FIG. 2.

Next, a conductive layer 7 is formed on the non-single-crystal semiconductor laminate member 3 made up of the non-single-crystal semiconductor layers 4, 5. Moreover, the energy band gap of layer 6 is, preferably larger than that of layer 5. and 6, that is, on the non-single-crystal semiconductor layer 6 (FIG. 1D).

The conductive layer 7 has such a structure that a light-transparent conductive layer 8 formed of, for example, a tin oxide or a light-transparent conductive material consisting principally of tin oxide, and a reflective conductive layer 9 formed of a metal, such as aluminum, silver or the like, are formed in this order. In this case, the conductive layer 8 is formed to a thickness of 900 to 1300 angstroms by means of, for example, vacuum evaporation, and the conductive layer 9 is also formed by vacuum evaporation.

In the manner described above, the first embodiment of the photoelectric conversion device of the present invention shown in FIG. 2A is manufactured.

With the photoelectric conversion device shown in FIG. 2A, when light 10 is incident on the side of the substate 1 towards the non-single-crystal semiconductor laminate member 3, electron-hole pairs are created in the I-type non-single-crystal semiconductor layer 5 in response to the light 10. The holes of the electron-hole pairs thus produced flow through the P-type non-single-crystal semiconductor layer 4 into the light-transparent conductive layer 2, and the electrons flow through the N-type non-single-crystal semiconductor layer 6 into the conductive layer 7. Therefore, photocurrent is supplied to a load which is connected between the conductive layers 2 and 7, thus providing the photoelectric conversion function.

In this case, the I-type non-single-crystal semiconductor layer 5 has a P-type impurity (boron) introduced thereinto which is distributed so that the impurity concentration continuously decreases towards the non-single-crystal semiconductor layer 6 in the thickness direction of the layer 5, as shown in FIG. 2B. On account of this, even if the I-type non-single-crystal semiconductor layer 5 is formed thick for generating therein a large quantity of electraonhole pairs in response to the incident of light, a depletion layer (not shown) which extends into the non-single-crystal semiconductor layer 5 from the PI junction 11 between the P-type non-single-crystal semiconductor layer 4 and the I-type non-single-crystal semiconductor layer 5 and a depletion (not shown) layer which extends into the non-single-crystal semiconductor layer 5 from the NI junction 12 between the N-type non-single-crystal semiconductor layer 6 and the non-single-crystal semiconductor layer 5 are joined together. Therefore, the I-type non-single-crystal semiconductor layer 5, as viewed from the bottom of the conduction band and the top of the valence bands of its enegy band, has a gradient that effectively causes holes and electrons drift towards the non-single-crystal semiconductor layers 4 and 6, respectively.

Accordingly, the photoelectric conversion device of the present invention, shown in FIG. 2A, achieves a higher photoelectric conversion efficiency than do the conventional photoelectric conversion devices.

A photoelectric conversion device corresponding to the conventional one and which is identical in construction with the photoelectric conversion device of the present invention shown in FIG. 2A, except that the concentration of the N-type impurity in the I-type non-single-crystal semiconductor layer 5 is about 10¹⁶ atoms/cm³ which is far lower than the impurity concentrations in the P-type and I-type non-single-crystal semiconductor layers 4 and 6 because the I-type non-single-crystal semiconductor layer 5 is formed to contain oxygen, and/or carbon, and/or phosphorus in large quantities, as referred to previously, provided a voltage V (volt)-current density I (mA/cm²) characteristic as indicated by curve 30 in FIG. 3. Accordingly, the open-circuit voltage was 0.89 V, the short-circuit current density I 16.0 mA/cm², the fill factor was 61%, and the photoelectric conversion efficiency about 8.7%. In contrast thereto, the photoelectric conversion device of the present invention shown in FIG. 2A, provided the voltage V -current density I characteristic as indicated by curve 31 in FIG. 3, obtained. Accordingly, the open-circuit voltage V was 0.92 V, which is higher than was with the abovesaid device corresponding to the prior art device; the current density I was 19.5 mA/cm²; the fill factor was 68%; and the photoelectric conversion efficiency was about 12.2%. Incidentally, these results were obtained under the conditions wherein the photoelectric conversion devices, each having the non-single-crystal semiconductor laminate member 3 of a 1.05 cm² area, were exposed to irradiation by light with an intensity of AM1 (100 mW/cm²).

In the case of the photoelectric conversion device of a present invention shown in FIG. 2A, since the I-type non-single-crystal semiconductor layer 5 has boron introduced thereinto as a P-type impurity the boron, combines with the oxygen and/or carbon and/or phosphorus contained in the non-single-crystal semiconductor layer 5. In addition, the concentration of the P-type impurity (boron) is high on the side of the PI junction 11, that is, on the side of the P-type non-single-crystal semiconductor layer 4. Accordingly, the expansion of the depletion layer extending into the I-type non-single-crystal semiconductor layer 5 from the PI junction 11 between the P-type non-single-crystal semiconductor layer 4 and the I-type non-single-crystal semiconductor layer 5 is hardly or only slightly diminished by the light irradiation effect (the Staebler-Wronski effect).

For this reason, according to the photoelectric conversion device of the present invention, the aforesaid high photoelectric conversion efficiency is hardly impaired by long-term use.

In addition the aforesaid photoelectric conversion device corresponding to the prior art one which provided the voltage V-current density I characteristeristic indicated by the curve 30 in FIG. 3, exhibited variations (%) in the photoelectric conversion efficiency relative to the light irradiation time T (hr) as indicated by curve 40 in FIG. 4. In contrast thereto, in the case of the photoelectric conversion device of the present invention, the photoelectric conversion efficiency varied with the light irradiation time T as indicated by curve 41 in FIG. 4. That is, the photoelectric conversion efficiency slightly increased in an early stage and, thereafter, it decreased only very slightly with time. These result were also obtained under the same conditions mentioned previously in connection with FIG. 3.

As described above, the first embodiment of the photoelectric conversion device of the present invention possesses the advantage that it provides a higher photoelectric conversion efficiency than do the conventional photoelectric conversion devices, even when used for a long period of time.

Further, the manufacturing method of the present invention shown in FIG. 1 employs a series of simple steps such as forming the conductive layer 2 on the substrate 1, forming the non-single-crystal semiconductor layers 4, 5 and 6 on the conductive layer 2 through the CVD method to provide the non-single-crystal semiconductor laminate member 3 and forming the conductor layer 7 on the non-single-crystal semiconductor laminate member 3, The I-type non-single-crystal semiconductor layer 5 is formed by a CVD method using a semiconductor raw material gas and a P-type deposit (boron) gas and, in this case, simply by continuously changing the concentration of the deposit material gas relative to the concentration of the semiconductor raw material gas as a function of time, the P-type impurity is introduced into the layer 5 with such a concentration distribution that its concentration continuously decreases towards the non-single-crystal semiconductor layer 6 in the thickness direction of the layer 5.

Accordingly, the manufacturing method of the present invention allows ease in the fabrication of the photoelectric conversion device of the present invention which has the aforementioned advantages.

Incidentally, the first embodiment illustrated in FIG. 2 shows the case in which the impurity contained in the I-type non-single-crystal semiconductor layer 5 has such a concentration distribution as shown in FIG. 2B in which the concentration linearly and continuously drops towards the non-single-crystal semiconductor layer 6.

As will be appreciated from the above, however, even if the impurity introduced in the I-type non-single-crystal semiconductor layer 5 has a concentration profile such that the impurity concentration drops stepwise and continuously towards the non-single-crystal semiconductor layer 6 as shown in FIG. 5 which illustrates a second embodiment of the present invention, and even if the impurity in the layer 5 has such a concentration distribution that the impurity concentration decreases non-linearily and continuously towards the layer 6 in a manner to obtain a concentration distribution such that the impurity concentration abruptly drops in the end portion of the layer 5 adjacent the layer 6 as shown in FIG. 6 which illustates a third embodiment of the present invention, the photoelectric conversion device of the present invention produces the same excellent operation and effects as are obtainable with the photoelectric conversion device shown in FIG. 2.

Further, the foregoing description has been given of the case where light is incident on the photoelectric conversion device from the side of the substrate 1 and, accordingly, the non-single-crytal semiconductor layer 4 of the non-single-crystal semiconductor laminate member 3 on the side on which the light is incident is P-type.

But, also in case where the photoelectric conversion device is arranged to be exposed to light on the side opposite from the substrate 1, the non-single-crystal semiconductor layer 6 of the non-single-crystal semiconductor laminate member 3 on the side of the incidence of light is P-type, the non-single-crystal semiconductor layer 4 on the side of the substrate 1 is N-type and the non-single-crystal semiconductor layer 5 has introduced thereinto a P-type impurity (boron) which is distributed so that the impurity concentration continuously decreases towards the non-single-crystal semiconductor layer 4 in the thickness direction of the layer 5, the same excellent operation and effects as described previously can be obtained, as will be understood from the foregoing description. In this case, however, the conductive layer 7 must be substituted with a light-transparent one. The substrate 1 and the conductive layer 2 need not be light-transparent.

While in the foregoing the non-single-crystal semiconductor laminate member 3 has one PIN junction, it is also possible to make the laminate member 3 have two or more PIN junctions and to form each of the two or more I-type non-single-crystal semiconductor layers so that the P-type impurity introduced therein may have the aforesaid concentration distribution.

It will be apparent that many modifications and variations may be effected without departing from the scope of the novel concepts of the present invention.

Claims

1. A method for manufacturing a photoelectric conversion device comprising the steps of:

forming a first impurity, non-single crystalline semiconductor layer of a first conductivity type on a substrate in a reaction chamber;

depositing a substantially intrinsic semiconductor layer on said first impurity layer by introducing process gas into said reaction chamber together with a dopant gas comprising boron, the introducing ratio of said dopant gas to said process gas being monotonically decreased throughout the deposition of the intrinsic semiconductor layer in order that the impurity concentration in said intrinsic semiconductor layer is monotonically decreased from the interface between said first impurity and intrinsic semiconductor layers;

forming a second impurity, non-single crystalline semiconductor layer of a second conductivity type opposite to said first conductivity type, the impurity semiconductor layer adjacent to the heavier doping side of said intrinsic layer having the same conductivity type as that corresponding to the dopant gas for said intrinsic semiconductor layer;

forming an electrode arrangement for said conversion device; and

reducing the oxygen concentration in said substantially intrinsic layer to a level less than 5×10¹⁹ atoms/cm³.

2. A manufacturing method according to claim 1 5, wherein the process gas is a hydride or halide of silicon and the dopant gas is a hydride or halide of boron.

3. A manufacturing method according to claim 2 5, wherein the concentration of the dopant gas relative to the concentration of the process gas is continuously decreased with time within a range of less than 5 ppm.

4. A method as in claim 3 where 5, wherein said level is as low as 5×10¹⁸ atoms/cm³.

5. A manufacturing method as in claim 1 where for manufacturing a photoelectric conversion device comprising the steps of:

forming a first impurity, non-single crystalline semiconductor layer of a first conductivity type on a substrate in a reaction chamber;

depositing a substantially intrinsic semiconductor layer on said first impurity layer by introducing process gas into said reaction chamber together with a dopant gas comprising boron, the introducing ratio of said dopant gas to said process gas being monotonically decreased throughout the deposition of the intrinsic semiconductor layer in order that the impurity concentration in said intrinsic semiconductor layer is monotonically decreased from the interface between said first impurity and intrinsic semiconductor layers;

forming a second impurity, non-single crystalline semiconductor layer of a second conductivity type opposite to said first conductivity type, the impurity semiconductor layer adjacent to the heavier doping side of said intrinsic layer having the same conductivity type as that corresponding to the dopant gas for said intrinsic semiconductor layer;

forming an electrode arrangement for said conversion device; and

reducing the oxygen concentration in said substantially intrinsic layer to a level less than 5×10¹⁹ atoms/cm³,

wherein the reduction of the oxygen concentration is effected by passing said process gas through a molecular sieve or zeolite which adsorbs oxygen.

6. A method of claim 1 5, wherein said semiconductor layer is made of amorphous semiconductor.

7. A method of claim 6 5, wherein said process gas is filtered in advance of introduction into said reaction chamber.

8. A method for manufacturing a photoelectric conversion device comprising the steps of:

forming a first impurity, non-single crystalline semiconductor layer of a first conductivity type on a substrate in a reaction chamber;

depositing a substantially intrinsic semiconductor layer on said first impurity layer by introducing process gas into said reaction chamber together with a dopant gas comprising boron, the introducing ratio of said dopant gas to said process gas being monotonically decreased throughout the deposition of the intrinsic semiconductor layer in order that the impurity concentration in said intrinsic semiconductor layer is monotonically decreased from the interface between said first impurity and intrinsic semiconductor layers;

forming a second impurity, non-single crystalline semiconductor layer of a second conductivity type opposite to said first conductivity type, the impurity semiconductor layer adjacent to the heavier doping side of said intrinsic layer having the same conductivity type as that corresponding to the dopant gas for said intrinsic semiconductor layer;

forming an electrode arrangement for said conversion device; and

reducing the carbon concentration in said substantially intrinsic layer to a level less than 4×10¹⁹ atoms/cm³.

9. A method as in claim 8 where 10, wherein said level is as low as 4×10¹⁵ atoms/cm³.

10. A manufacturing method as in claim 8 method for manufacturing a photoelectric conversion device comprising the steps of:

forming a first impurity, non-single crystalline semiconductor layer of a first conductivity type on a substrate in a reaction chamber;

depositing a substantially intrinsic semiconductor layer on said first impurity layer by introducing process gas into said reaction chamber together with a dopant gas comprising boron, the introducing ratio of said dopant gas to said process gas being monotonically decreased throughout the deposition of the intrinsic semiconductor layer in order that the impurity concentration in said intrinsic semiconductor layer is monotonically decreased from the interface between said first impurity and intrinsic semiconductor layers;

forming a second impurity, non-single crystalline semiconductor layer of a second conductivity type opposite to said first conductivity type, the impurity semiconductor layer adjacent to the heavier doping side of said intrinsic layer having the same conductivity type as that corresponding to the dopant gas for said intrinsic semiconductor layer;

forming an electrode arrangement for said conversion device; and

reducing the carbon concentration in said substantially intrinsic layer to a level less than 4×10¹⁸ atoms/cm³;

wherein the reduction of the carbon concentration is effected by passing said process gas through a molecular sieve or zeolite which adsorbs carbon.

11. A method for manufacturing a photoelectric conversion device comprising the steps of:

forming a first impurity, non-single crystalline semiconductor layer of a first conductivity type on a substrate in a reaction chamber;

depositing a substantially intrinsic semiconductor layer on said first impurity layer by introducing process gas into said reaction chamber together with a dopant gas comprising boron, the introducing ratio of said dopant gas to said process gas being monotonically decreased throughout the deposition of the intrinsic semiconductor layer in order that the impurity concentration in said intrinsic semiconductor layer is monotonically decreased from the interface between said first impurity and intrinsic semiconductor layers;

forming a second impurity, non-single crystalline semiconductor layer of a second conductivity type opposite to said first conductivity type, the impurity semiconductor layer adjacent to the heavier doping side of said intrinsic layer having the same conductivity type as that corresponding to the dopant gas for said intrinsic semiconductor layer;

forming an electrode arrangement for said conversion device; and

reducing the phosphorus concentration in said substantially intrinsic layer to a level less than 5×10¹⁵ atoms/cm³.

12. A method as in claim 11 where said level is as low as 5×10¹⁵ atoms/cm³.

13. A manufacturing method as in claim 11 where the reduction of the phosphorus concentration is effected by passing said process gas through a molecular sieve or zeolite which adsorbs phosphorus.

14. A method as in claims 1, 8, or 11 where 5 or 10, wherein said first conductivity type is n-type and said second conductivity type is p-type.

15. A method as in claims 1, 8, or 11 where 5 or 10, wherein said first conductivity type is p-type and said second conductivity type is n-type.

16. A method as in claims 1, 8, or 11 where 5 or 10, wherein the ratio of said impurity concentration at the interface between said second impurity and intrinsic semiconductor layers to that at said interface between said first impurity and the intrinsic semiconductor layers is 1/10 to 1/100.

17. A method as in claim 16 where wherein said ratio is 1/20 to 1/40.

18. A method as in claims 1, 8, or 11 where 5 or 10, wherein said impurity is boron and the boron concentration at said interface between the p-type and intrinsic layers is 2×10¹⁵ to 2×10¹⁷ atoms/cm³.

19. A method as in claims 1, 8, or 11 where 5 or 10, wherein said first layer comprises p-type, non-single crystalline Si_xC_1-x (0<x<1) and said impurity comprises boron.