NOVELTY - A solid-state p-n heterojunction comprises an organic polymeric p-type material in contact with a porous layer of n-type material, where the boundary between the p-type layer and the n-type layer is functionalized with at least a partial monolayer of functionalized electron acceptor moieties and optionally sensitizing agents.    USE - The solid-state p-n heterojunction is useful for manufacturing an optoelectronic device such as a photovoltaic cell, phototransistor or light sensing device (all claimed).    ADVANTAGE - The solid-state p-n heterojunction effectively produces improved optoelectronic devices.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are:    (1) an optoelectronic device comprising at least one solid state p-n heterojunction;    (2) use of at least a partial monolayer of functionalized electron acceptor moieties and optionally sensitizing agents to enhance the efficiency of a solid state polymer solar cell, and to increase the photo induced electron transfer from the polymer to the n-type layer; and    (3) a method for the manufacture of the solid-state p-n heterojunction comprising the organic p-type material in contact with a porous layer of n-type material, comprising: (a) coating an anode, preferably a transparent anode (e.g. a fluorine doped tin oxide (FTO) anode) with a compact layer of an n-type semiconductor material; (b) forming a porous (preferably mesoporous) layer of an n-type semiconductor material on the compact layer, (c) forming at least a partial monolayer of functionalized electron acceptor moieties and optionally sensitizing agents on the surface of the porous n-type layer; (d) optionally treating the compact layer and/or the porous layer of n-type material with at least one ionic material such as a lithium salt; (e) optionally forming a porous barrier layer of an insulating material on the porous layer of n-type material; (f) contacting the porous layer of n-type material with at least one solution of at least one polymeric organic p-type semiconductor material where to form a layer of polymeric organic p-type semiconductor interpenetrating the porous layer of an n-type material; (f2) optionally treating the layer produced in (f) by coating on top with a solution of ionic material, such as lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI); (g) forming a cathode, preferably a metal cathode (e.g. a silver or gold cathode) in contact with the p-type semiconductor material.