NOVELTY - Use of conjugated azomethine molecule having a definite molecular weight is claimed for photovoltaic film application as electron donor. The molecule having a molecular mass of 300-3000 comprises aromatic entity (A) consisting of (A1) greater than or equal to 1 nitrogen atom directly attached to aromatic entity or (Aii) greater than or equal to 1 carbon atom directly attached to aromatic entity, and aromatic heterocyclic bridging entity (B') having a connecting nitrogen-carbon double bond (azomethine) and consisting of greater than or equal to 1 carbon atom directly attached to aromatic heterocyclic entity and to nitrogen atom in case of (Ai).    USE - Use of conjugated azomethine molecule having a definite molecular weight in a photovoltaic film application as electron donor used in photovoltaic device, solar cell, film, and sensor for detecting intensity and/or frequency of light (all claimed).    ADVANTAGE - The small azomethine molecule has photovoltaic characteristics, e.g. high photovoltaic performance even for non-optimized molecules, which provide reliable results without jeopardizing functionality and advantages, excellent optical properties and thermal stability, good solubility and film-forming properties, and low cost.    DETAILED DESCRIPTION - Use of conjugated azomethine molecule having a definite molecular weight is claimed for photovoltaic film application as electron donor. The molecule having a molecular mass of 300-3000 comprises aromatic entity (A) consisting of (A1) greater than or equal to 1 nitrogen atom directly attached to aromatic entity represented by formula B'-C=N-A (5a) or (Aii) greater than or equal to 1 carbon atom directly attached to aromatic entity represented by formula A-C=N-B' (5b), and aromatic heterocyclic bridging entity (B) having a connecting nitrogen-carbon double bond (azomethine) and consisting of greater than or equal to 1 carbon atom directly attached to aromatic heterocyclic entity and to nitrogen atom in case of (Ai) or greater than or equal to 1 nitrogen atom directly attached to aromatic heterocyclic entity and to carbon atom in case of (Aii). The molecule has structure of formulae (A-B')n-A (5c), Am-B' (5d), and/or B'r-A (5e). Component (A) has molecular mass of 64-1250 and 1-4 aromatic ring structures, and component (B') has molecular mass of 65-1500 and 1-4 aromatic ring structures.    A=aromatic entity;    B'=aromatic heterocyclic bridging entity comprising S, N, P, Si, Se, and/or O; and    n,m,r=1-5.    INDEPENDENT CLAIMS are included for:    (1) conjugated photovoltaic azomethine having definite molecular weight comprising 4-aminotriphenylamine-R2 (TPA) of formula (4), where bridging entity is selected from 2,5-thiophenedicarbaldehyde (Th), 2,3-dihydrothieno(3,4-b)(1,4)dioxine-5,7-dicarbaldehyde (EDOT), 2,2'-bithiazole-5,5'-dicarbaldehyde (BTz), and/or 4,7-bis(5-formylthiophen-2-yl)-2,1,3-benzothiadiazole (TBT);    (2) production of conjugated photovoltaic azomethine which involves condensing component (A) under suitable conditions, adding electron acceptor to form solution, directly applying condensate as a solution into film on a substrate by e.g. spin-coating, optionally washing the separated condensate, and annealing the condensate at 50-150 degrees C for 10-60 minutes;    (3) photovoltaic device comprising the photovoltaic film, substrate, anode layer, bulk hetero junction layer containing photovoltaic molecule as electron donor, and electron acceptor molecules, such as copper phthalocyanine, carbon fullerene, and fullerene derivative, such as (60)phenyl-C61-butyric acid methyl ester (PCBM), (70)PCBM, and cathode layer;    (4) solar cell comprising photovoltaic molecule and/or photovoltaic device; and    (5) sensor for detecting intensity and/or frequency of light comprising film or photovoltaic molecule.    R=H, -CN, OAlk, and/or Alk; and    Alk=alkanes.    DESCRIPTION OF DRAWING(S) - The drawings show the synthesis route and molecular structures of the small-molecule azomethines.