Variable light transmission device comprising electrophoretic medium having a compination of light reflective and light absorbing pigment particles

A variable light transmission device comprising:

• a first light transmissive electrode layer;
• a second light transmissive electrode layer;
• and a microcell layer, the microcell layer being disposed between the first light transmissive electrode layer and the second light transmissive electrode layer, the microcell layer comprising a plurality of microcells and a sealing layer, each microcell of the plurality of microcells including an electrophoretic medium, the electrophoretic medium comprising a first type of electrically charged pigment particles, a second type of electrically charged pigment particles, a charge control agent, and a non-polar liquid, each microcell of the plurality of microcells having a microcell opening, the sealing layer spanning the microcell openings of the plurality of microcells, each microcell of the plurality of microcells comprising a microcell bottom layer, a protrusion structure, microcell walls, and a channel, the microcell bottom layer having a microcell bottom inside surface, the microcell bottom inside surface comprising an exposed microcell bottom inside surface and an unexposed microcell bottom inside surface, the protrusion structure having a protrusion base, a protrusion surface, a protrusion apex, and a protrusion height, the protrusion apex being a point or a set of points of the protrusion structure, the point or the set of points having shorter distance from the microcell opening than all other points of the protrusion structure, the protrusion height being the distance between the protrusion base and the protrusion apex, the protrusion surface being the surface of the protrusion structure not including the protrusion apex that is in contact with the electrophoretic medium, the microcell walls having a microcell inside wall surface and a microcell wall upper surface, the microcell inside wall surface being the surface of the microcell walls of a microcell that is in contact with the electrophoretic medium, the microcell wall upper surface being the surface of the microcell walls of a microcell that is in contact with the sealing layer, the channel having a channel height, the channel height being 50% of the protrusion height, the unexposed microcell bottom inside surface being in contact with the protrusion base, the channel being a volume between the exposed microcell bottom inside surface, the protrusion surface, and the microcell inside wall surface;
• wherein the first type of electrically charged pigment particles are light reflecting and the second type of electrically charged pigment particles are light absorbing, wherein the first type of electrically charged pigment particles have a same charge polarity as the second type of charged pigment particles, wherein the first type of electrically charged pigment particles have an average particle size that is larger than the average particle size of the second type of charged pigment particles, and wherein either:
• the first type of electrically charged pigment particles and the second type of electrically charged pigment particles are positive, and wherein the zeta potential of the first type of electrically charged pigment particles is lower than the zeta potential of the second type of electrically charged pigment particles or the first type of electrically charged pigment particles and the second type of electrically charged pigment particles are negative, and wherein the zeta potential of the first type of electrically charged pigment particles is higher than the zeta potential of the second type of electrically charged pigment particles.