| US 7,521,855 B2 | ||
| Electronic appliance and light-emitting device | ||
| Junichiro Sakata, Kanagawa (Japan); Hisao Ikeda, Kanagawa (Japan); and Takahiro Kawakami, Kanagawa (Japan) | ||
| Assigned to Semiconductor Energy Laboratory Co., Ltd., (Japan) | ||
| Filed on Dec. 01, 2005, as Appl. No. 11/291,312. | ||
| Claims priority of application No. 2004-353427 (JP), filed on Dec. 06, 2004. | ||
| Prior Publication US 2006/0119258 A1, Jun. 08, 2006 | ||
| Int. Cl. H05B 33/00 (2006.01) | ||
| U.S. Cl. 313—504 [313/506; 428/917] | 20 Claims |
| 1. A light-emitting device comprising:
at least one light-emitting element including:
a first electrode;
a first material layer over the first electrode;
a layer including an organic compound over the first material layer;
a second material layer over the layer including the organic compound; and
a second electrode over the second material layer,
wherein the first material layer has symmetric current-voltage characteristics with respect to the zero point in a graph having
the abscissa axis showing current values and the ordinate axis showing voltage values; and
wherein the second material layer has the same current-voltage characteristic as the first material layer.
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