Abstract: The present invention further improves the measurement accuracy of the viscosity of an ink composition. An ink composition for forming a functional layer of an organic photoelectric conversion element, wherein an electron spin concentration per 1 L of volume of the ink composition is 250×1016 or less. The ink composition may be an ink composition containing a solvent and a p-type semiconductor material. The ink composition may be an ink composition in which the p-type semiconductor material contains a polymer compound having an electron spin concentration per 1 g of weight of 70×1016 or less. The ink composition may be an ink composition in which the solvent contains one or more types of organic solvents and the p-type semiconductor material contains a ?-conjugated polymer compound containing a donor constitutional unit and an acceptor constitutional unit.

Abstract: The present invention provides an organic photoelectric conversion material such that an increase in the solution viscosity can be suppressed even after long-term storage. This organic photoelectric conversion material comprises Pd, wherein the average number of Pd clusters in a scanning transmission electron microscopic image of a thin film made of the organic photoelectric conversion material is 1500 counts/?m3 or less. It is preferable that the Pd clusters each have a particle diameter of from 1 nm to 20 nm. It is preferable that the organic photoelectric conversion material is a polymer for organic photoelectric conversion material; and it is more preferable that the polymer for organic photoelectric conversion material is a D-A type n-conjugated polymer. It is preferable that the polymer for organic photoelectric conversion material has a thiophene ring.

Abstract: Provided is a method for producing a ?-conjugated polymer capable of suppressing an increase in dark current of an organic photoelectric conversion element even if the method includes a purification step including heating. A method for producing a ?-conjugated polymer includes: step (I) of heating and dissolving a crude ?-conjugated polymer in a solvent to obtain a polymer solution; and step (II) of precipitating a ?-conjugated polymer from the polymer solution. In step (I), the content of peroxide in the solvent is 0.1% or less in terms of a relative area ratio measured by high-performance liquid chromatography, and the electron spin concentration of the ?-conjugated polymer is 30×1016 Spin/g or less and/or 2.5 times or less the electron spin concentration of the crude ?-conjugated polymer.