NOVELTY - Preparation of thin film solar cell based on narrow-band gap conjugated polymer involves dissolving poly(2,6-(4,4-di-(2-ethylhexyl)-cyclopenta dithiophene)-4 7-diazosulfide) and (6,6)-2-phenyl-C61-2-methyl butyrate in chlorobenzene solvent, adding 1,3-dimethyl imidazolone, etching indium tin oxide anode layer on glass substrate, drying, coating poly (3,4-epidioxy ethylthiophene) and polystyrene sulfonate solution as anode modification layer, coating photosensitive layer, vacuumizing and evaporating aluminum cathode layer.    USE - Preparation of thin film solar cell based on narrow-band gap conjugated polymer.    ADVANTAGE - Two-phase separation scale of electron donor and electron acceptor in the photosensitive layer, transmission path of photo-generated electron and cavity, transmission efficiency and collection efficiency of photo-generated charge are improved, series resistance of cell is reduced, short circuit current is improved by 36% and energy conversion efficiency is improved by 40%.    DETAILED DESCRIPTION - Preparation of thin film solar cell based on narrow-band gap conjugated polymer involves dissolving the 7 g/ml poly(2,6-(4,4-di-(2-ethylhexyl)-cyclopenta dithiophene)-4,7-diazosulfide) and 21 mg/ml (6,6)-2-phenyl-C61-2-methyl butyrate in chlorobenzene solvent at 1/3 mass ratio in a reaction box with inert atmosphere to obtain mixed solution (I), stirring for 2 hours at 50 degrees C, stopping heating, continuously stirring for 12 hours, adding 20-70 ml 1,3-dimethyl imidazolone to every mu l of mixed solution I, continuously stirring for 12 hours to obtain mixed solution (II), etching the indium tin oxide anode layer (2) on the glass substrate (1) to thin strip shape, washing the etched thin strip-shaped indium tin oxide processed piece, drying in an oven at 120 degrees C, placing the processed piece on a support stand of film coating machine, uniformly coating poly (3,4-epidioxy ethylthiophene) and polystyrene sulfonate solution using a 0.45 mu filter head, spin coating to form film at revolution speed of 3000 r/min until a film with thickness of 40 nm is formed, setting it as the anode modification layer (3), heating for 30 minutes in oven at 120 degrees C, transferring the dried processing piece with anode modification layer (3) to reaction box, cooling, placing on support stand of the film coating machine, uniformly coating the stirred mixed solution II on the upper surface of the anode modification layer (3) using 0.45 mu m filter head, spin coating to form film at revolution speed of 900 r/minute and setting as photosensitive layer (4) with thickness of 100 nm, taking out from the reaction box to a transferring bottle, placing in a vacuum film plating machine, vacuumizing and evaporating the aluminum cathode layer (5) with thickness of 80 nm when the vacuum degree is 4asterisk10-4 Pa. The solar cell has orderly connected glass substrate (1), indium tin oxide anode layer (2), anode modification layer (3) consists of poly (3,4-epidioxy ethylthiophene) and polystyrene sulfonate, photosensitive layer (4) consists of narrow band gap conjugated polymer and fullerene derivative, and aluminum cathode layer (5). Narrow band gap conjugated polymer is poly(2,6-(4,4-di-(2-ethylhexyl)-cyclopenta dithiophene)-4,7-diazosulfide). The fullerene derivative is (6,6)-2-phenyl-C61-2-methyl butyrate.