According to one embodiment, a photodetector includes a first conductive layer, a second conductive layer, and an organic layer provided between the first conductive layer and the second conductive layer. The organic layer includes a first region and a second region. The second region is provided between the first region and the second conductive layer. The first region includes a first compound and a second compound. The first compound includes a first mother skeleton. The second region includes the first compound and a third compound. The third compound includes the first mother skeleton. The third compound is different from the first compound. The second region does not include the second compound, or a concentration of the second compound in the second region is lower than a concentration of the second compound in the first region.