In the case of p-type Cu2O, its relatively small bandgap (2.0 eV) allows for a theoretical maximum photocurrent density of up to 14.9 mA cm -2 . Its exceptionally long carrier diffusion length (3-10 m), high mobility (~100 cm 2 V -1 s -1 ), and high light absorption coefficient (>10 cm -1 ) also enable the use of a sufficient thickness of Cu2O for effective light absorption .