A phototransistor for converting optical energy into electrical energy, the phototransistor comprising: one or more photoelectric conversion elements (PE14 - 19, PE24 - 29, PE34 - 39, PE110 - 210, PE120 - 420), wherein each of the one or more photoelectric conversion elements comprises: a photoactive layer (PA10 - 19, PA24 - 29, PA34 - 39, PA110 - 210, PA120 - 420) comprising: a quantum dot layer (QL10 - 19, QL24 - 29, QL34 - 39, QL110 - 210, QL120 - 420) configured to generate an electric charge in response to light incident thereon, and a semiconductor layer (SL10 - 19, SL24 - 29, SL34 - 39, SL 110 - 210, SL120 - 420) configured to conduct the electric charge generated by the quantum dot layer; wherein the quantum dot layer (QL10 - 19, QL24 - 29, QL34 - 39, QL110 - 210, QL120 - 420) is embedded in or provided on the semiconductor layer (SL10 - 19, SL24 - 29, SL34 - 39, SL 110 - 210, SL120 - 420); a lateral electrode (E10 - 13, E16 - 19, E36 - 39, E56 - 59, E110, E310, E120, E320, E520, E720) electrically connected to a first side of the semiconductor layer; and a further lateral electrode (E20 - 23, E26 - 29, E46 - 49, E66 - 69, E210, E410, E220, E420, E620, E820) electrically connected to a second side of the semiconductor layer; and at least one gate electrode (G10 - 13, G16 - 19, G26, G36) configured to apply an electric field to at least one of the one or more photoelectric conversion elements and provided below or above the at least one of the one or more photoelectric conversion elements. one or more photoelectric conversion elements (PE14 - 19, PE24 - 29, PE34 - 39, PE110 - 210, PE120 - 420), wherein each of the one or more photoelectric conversion elements comprises: a photoactive layer (PA10 - 19, PA24 - 29, PA34 - 39, PA110 - 210, PA120 - 420) comprising: a quantum dot layer (QL10 - 19, QL24 - 29, QL34 - 39, QL110 - 210, QL120 - 420) configured to generate an electric charge in response to light incident thereon, and a semiconductor layer (SL10 - 19, SL24 - 29, SL34 - 39, SL 110 - 210, SL120 - 420) configured to conduct the electric charge generated by the quantum dot layer; wherein the quantum dot layer (QL10 - 19, QL24 - 29, QL34 - 39, QL110 - 210, QL120 - 420) is embedded in or provided on the semiconductor layer (SL10 - 19, SL24 - 29, SL34 - 39, SL 110 - 210, SL120 - 420); a lateral electrode (E10 - 13, E16 - 19, E36 - 39, E56 - 59, E110, E310, E120, E320, E520, E720) electrically connected to a first side of the semiconductor layer; and a further lateral electrode (E20 - 23, E26 - 29, E46 - 49, E66 - 69, E210, E410, E220, E420, E620, E820) electrically connected to a second side of the semiconductor layer; a photoactive layer (PA10 - 19, PA24 - 29, PA34 - 39, PA110 - 210, PA120 - 420) comprising: a quantum dot layer (QL10 - 19, QL24 - 29, QL34 - 39, QL110 - 210, QL120 - 420) configured to generate an electric charge in response to light incident thereon, and a semiconductor layer (SL10 - 19, SL24 - 29, SL34 - 39, SL 110 - 210, SL120 - 420) configured to conduct the electric charge generated by the quantum dot layer; wherein the quantum dot layer (QL10 - 19, QL24 - 29, QL34 - 39, QL110 - 210, QL120 - 420) is embedded in or provided on the semiconductor layer (SL10 - 19, SL24 - 29, SL34 - 39, SL 110 - 210, SL120 - 420); a quantum dot layer (QL10 - 19, QL24 - 29, QL34 - 39, QL110 - 210, QL120 - 420) configured to generate an electric charge in response to light incident thereon, and a semiconductor layer (SL10 - 19, SL24 - 29, SL34 - 39, SL 110 - 210, SL120 - 420) configured to conduct the electric charge generated by the quantum dot layer; wherein the quantum dot layer (QL10 - 19, QL24 - 29, QL34 - 39, QL110 - 210, QL120 - 420) is embedded in or provided on the semiconductor layer (SL10 - 19, SL24 - 29, SL34 - 39, SL 110 - 210, SL120 - 420); a lateral electrode (E10 - 13, E16 - 19, E36 - 39, E56 - 59, E110, E310, E120, E320, E520, E720) electrically connected to a first side of the semiconductor layer; and a further lateral electrode (E20 - 23, E26 - 29, E46 - 49, E66 - 69, E210, E410, E220, E420, E620, E820) electrically connected to a second side of the semiconductor layer; and at least one gate electrode (G10 - 13, G16 - 19, G26, G36) configured to apply an electric field to at least one of the one or more photoelectric conversion elements and provided below or above the at least one of the one or more photoelectric conversion elements.