TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Components: The electron accepting material and the electron donating material are heat treated before, during or after being treated by the non-solvent. When the non-solvent is applied on the photoactive layer for 1-60 mm, a permeation distance of the non-solvent into the photoactive layer is greater than or equal to 5% and less than 50% of a thickness of the photoactive layer. The non-solvent is at least one or two of water, alkanes, halohydrocarbons, ethers, ketones, esters, nitrogen compounds, sulfur compounds, acids, alcohols, phenols, and polyols. The electron accepting material is a fullerene derivative or a non-fullerene derivative. The electron donating material includes at least one kind of electron donor, or a polymer of at least one kind of electron acceptor and at least one kind of electron donor. The electron donating material includes a polymer comprising an heterocyclic ring units of formula (A1)-(A3), a fused heterocyclic ring unit of formula (B1) and an anhydride unit of formula (C1). The non-solvent is: a nitrogen compound non-solvent; acetonitrile; or at least one or two of alkanes, ethers, alcohols or acids. The non-solvent is methanol or 2-methoxyethanol. A temperature of the heat treatment is a glass transition temperature (Tg) or more and a thermal decomposition temperature or less of the electron donating material. The electron accepting material is (6,6)-phenyl C-butyric acid methyl ester (PCBM), and the electron donating material is poly(3-hexylthiophene) (P3HT) or a polymer comprising a 3-methyl-1-(5-(7-(5-methyl-thiophen-2-yl)-benzo(1,2,5)thiadiazol-4-yl)-thiophen-2-yl)-thieno(3,4-c)pyrrole-4,6-dioneunit of formula (Q1).X1-X5 = CRR1a, NR, O, SiRR1a, PR, S, GeRR1a, Se or Te;Y3-Y5 = CR, N, SiR, P or GeR; eitherR2-R4, R, R1 = alkyl, cycloalkyl, alkoxy, aryloxy, alkylthioxy, arylthioxy, alkylsulfoxy, arylsulfoxy, alkenyl, silyl, boron, alkylamine, aralkylamine, arylamine, heteroarylamine, aryl, fluorenyl, carbazole, heterocyclyl including at least one N, O and S (all optionally substituted), H, deuterium, halo, nitrile, nitro, imide, amide or OH; ortwo adjacent substituent groups of R2-R4 or RR1a = condensation cycle;f, g = 0-2;x, y = mole fraction and is greater than 0 to less than 1;n = 1-10000; andR10-R12 = alkyl, alkoxy (both optionally substituted) or H.In the photovoltaic cell, a ratio (I(C=C)/I(C-C)) of an antisymmetric value and a symmetric value of an absorption spectrum of Fourier transform infrared spectroscopy is increased by 110-150% as compared to an intrinsic value of the electron accepting material and the electron donating material. Preferred Method: The method further comprises performing heat treatment before, during or after the performing of the surface treatment by the non-solvent.