In order to use renewable energy, development of technology using a photovoltaic effect becomes increasingly important. As a result of such development of technology, improvement of a photoelectric conversion element is advanced. The photoelectric conversion element includes an electricity-generating type element which converts light into electrical energy, and a light-emitting type element which, on the contrary, converts electrical energy into light. Both types of elements have substantially the same structure, but they use different materials for a layer disposed between electrodes. The former uses a photoelectric conversion material to form an electricity-generating type element, and the latter uses a light-emitting material to form a light-emitting type element.
Typical examples of the former include solar cells, while typical examples of the latter include light-emitting diodes. The solar cells include inorganic solar cells and organic solar cells. Examples of the inorganic solar cells include crystalline (polycrystalline) silicon solar cells and amorphous silicon solar cells, both made of silicon, CIGS (Copper Indium Gallium Diselenide) solar cells using a compound semiconductor. Along with expansion of the solar cell market, low-cost and high-performance solar cells have been demanded. On the other hand, examples of the organic solar cells include organic thin-film solar cells. Since the solar cells of this type use dye and polymers as raw material, material costs are low. Furthermore, since a printing technique by, for example, coating can be used, the manufacturing process is facilitated, and thus, the cost can be largely reduced and the area can be increased.
The conversion efficiency of an organic thin-film solar cell has been improved by mixing a p-type semiconductor as a donor material and an n-type semiconductor as an acceptor material with each other to form a bulk hetero layer. In particular, it is desired to increase the P-N junction interface.
FIG. 5 is a sectional view of a conventional photoelectric conversion element (a type of converting light into electrical energy). The photoelectric conversion element includes base member 11, first electrode layer 13 formed on base member 11, photoelectric conversion layer 14, and second electrode layer 17. Furthermore, in order to improve the conversion efficiency, development of a technique for increasing a surface area of first electrode layer 13 and a technique for improving efficiency by a surface plasmon effect has been also carried out actively.
On the other hand, in an organic EL element as one type of the light-emitting diode, in order to improve the performance, a study for improving electron injection efficiency by forming asperities on an electrode surface, a study for enhancing light-emitting efficiency by interaction with a light-emitting body neighboring an electrode by resonance with the surface plasmon, are carried out actively.
Note here that prior art information relating to the invention of the present application includes, for example, PTLs 1 to 3 and NPLs 1 and 2.