The　effect　of　crystallization　of　polymeric　carbon　nitride　(PCN)　on　the　photocatalytic　CO2　reduction　activity　of　a　three-component　hybrid　comprising　a　Ru(II)　binuclear　complex　(RuRu),　Ag　nanoparticles,　and　PCN,　was　investigated.　Crystallized　carbon　nitride　(CCN)　obtained　by　heat　treatment　of　PCN　in　a　eutectic　LiCl–KCl　mixture　was　a　much　better　hybrid　photocatalyst　component　than　the　poorly　crystallized　PCN.　The　photocatalytic　activity　of　CCN　was　dependent　on　the　temperature　of　the　LiCl–KC　treatment:　Increasing　the　treatment　temperature　improved　the　photocatalytic　activity　as　much　as　five-fold　however,　treatment　at　elevated　temperatures　(＞798　K)　had　a　detrimental　effect.　Also,　a　substantial　PCN　crystallization　effect　was　promoted　by　the　construction　of　another　hybrid　photocatalyst　from　a　mononuclear　Ru(II)　complex　catalyst.　Time-resolved　microwave　photoconductivity　measurements　revealed　a　good　correlation　between　the　photocatalytic　activity　and　the　photoconductivity–charge　carrier　lifetime　product　in　the　CCN　samples　heated　at　milder　temperatures　(≤798　K).　For　CCN　specimens　heated　at　higher　temperatures,　appreciable　electron　accumulation　was　observed　during　the　photocatalytic　reaction,　indicating　that　the　accumulated　electrons　could　not　participate　in　the　CO2　reduction　reaction.　Thus,　the　crystallization　of　PCN　at　milder　temperatures　improved　the　mobility　and　lifetime　of　photogenerated　charge　carriers,　thereby　contributing　to　enhanced　photocatalytic　activity　toward　CO2　reduction.　©　2024　Chinese　Chemical　Society.　All　rights　reserved.