NOVELTY - A perovskite quantum dot nanocrystal is prepared by adding organic amine solution into round bottom flask, placing flask into ice salt bath, stirring under argon (Ar) protection, slowly adding excess concentrated aqueous hydrohalogenic acid, completely reacting, performing rotary evaporation to remove solvent and separate organic amine salt product powder, adding powder into conical flask, stirring anhydrous ether to dissolve impurities, filtering to obtain powder, repeatedly filtering for 3 times to obtain pure crystal, vacuum drying in vacuum drying chamber, heating, cooling, and separating.    USE - Preparation of perovskite quantum dot nanocrystal (claimed).    ADVANTAGE - Product is low-cost, easy to assemble, and stable and has high photoelectric conversion efficiency.    DETAILED DESCRIPTION - A perovskite quantum dot nanocrystal is prepared by adding organic amine solution RNH2 into round bottom flask, placing flask into ice salt bath, stirring under argon (Ar) protection, slowly adding excess concentrated aqueous hydrohalogenic acid of formula (HX), completely reacting, performing rotary evaporation to remove solvent and separate organic amine salt product powder of formula (RNH3X), adding RNH3X into conical flask, stirring anhydrous ether to dissolve impurities, filtering to obtain powder, repeatedly filtering for 3 times to obtain purified RNH3X, vacuum drying in vacuum drying chamber to obtain pure dry RNH3X, placing into dryer, adding RNH3X and PbX2 to 2 mixed solvent, heating sealed device under argon (Ar) protection while stirring, completely reacting, slowly cooling, separating crystal, filtering to obtain RNH3PbX3 perovskite crystal crude product, adding RNH3PbX3 into conical flask, stirring anhydrous ether to dissolve impurities, filtering to obtain powder, repeatedly filtering for 3 times to obtain pure RNH3PbX3 crystal, and drying in vacuum drying chamber. An INDEPENDENT CLAIM is included for application of quantum point solar cell using perovskite quantum dot nanocrystal which involves selecting n-type semiconductor material from porous nano titanium dioxide (TiO2), preparing RNH3PbX3 crystal dubbed solution, spin-coating with electric conductive glass fluorine doped tin oxide (FTO) layer to obtain RNH3PbX3 thin film, spin-coating with titanium dioxide (TiO2), using poly(3,4-ethylenedioxythiophene) (PEDOT):poly(sodium styrene sulfonate) (PSS) as hole transmitting material and platinum back assembly into perovskite quantum point solar energy battery device.