Photodetectors for weak-signal detection fabricated from ZnO:(Li,N) films

•ZnO films with carrier concentration as low as 5.0×1013cm−3 have been prepared via a lithium and nitrogen codoping method.•Ultraviolet photodetector that can detect weak signal with power density as low as 20 nw/cm2 have been fabricated from the ZnO:(Li,N) films.•The detectivity and noise equivalent power of the photodetector can reach 3.60×1015cmHz1/2/W and 6.67×10−18W−1, both of which are amongst the best values ever reported for ZnO photodetectors.