Highly sensitive, air-stable photodetectors based on single sub-micrometer organic crystalline ribbons self-assembled and deposited on the substrate via simple solution processing are achieved on both glass substrates and flexible substrates. The photoconductivity gain is about 1.3 x 10(3), while the responsivity is about 420 A W-1 at a field of 2 x 10(4) V cm(-1). The highest on/off ratio reaches around 1000.