During our investigation of perovskite solar cell materials, we serendipitously discovered an unusual photoconductive property of polyiodide, which can be enhanced greatly through the interaction of in situ-formed polyiodide and 3-thiophenemethylamine salt. This communication examined the photoconductive properties of polyiodide with and without adding different aromatic methylamine compounds. MATPI2 exhibits a high photoconductivity and short response time. The enhanced photoelectric conversion efficiencies are attributed to the strong interaction of polyiodide and the 3-thiophenemethylamine salt.