A　metal-insulator-semiconductor　(MIS)　ternary　photo-system　was　intricately　crafted　through　precise　amalgamation　polyvinylpyrrolidone　(PVP)-capped　metal　Cu　with　typical　covalent　triazine　framework　CTF-1　via　electrostatic　self-assembly.　The　2　%　Cu-PVP-CTF　exhibited　an　impressive　CH4　yield　of　80.7　mu　mol　&　sdot;g　�　1　&　sdot;h-　1　with　selectivity　of　96.8　%　under　visible　light,　representing　a　2.3-fold　and　112-fold　improvement　over　Schottky-type　Cu-CTF　and　pristine　CTF-1,　respectively.　In-situ　XPS　and　VASP-diff　calculations　unfolded　that　the　ultrathin　PVP　insulating　layer　significantly　expedited　interfacial　charges　tunneling,　corroborated　by　smaller　lifetime　tau　2　determined　via　femtosecond　transient　absorption　spectroscopy.　The　intermediates　of　paramount　importance　in　CO2　reduction　like　*COOH　and　*HCHO　were　meticulously　monitored　by　in-situ　Fourier　infrared　spectroscopy.　DFT　calculations　elucidated　that　Cu-PVP-CTF　was　notably　more　adept　at　facillitating　the　rate-determining　step　(*COOH　-＞　*CO)　to　produce　CH4　than　Cu-CTF.　This　work　tamps　the　groundwork　for　conceptional　roadmap　in　designing　novel　MIS　photo-system　for　CO2　conversion.