NOVELTY - Solid state positive-negative (p-n) heterojunction comprises an organic p-type material in contact with an n-type material, where (i) the n-type material is surface-sensitized by at least two sensitizing agents comprising a donor sensitizing agent and an acceptor sensitizing agent and optionally at least one intermediate sensitizing agent, (ii) the emission spectrum of the donor sensitizing agent overlaps with the absorption spectrum of the acceptor sensitizing agent and/or with the absorption spectrum of at least one intermediate sensitizing agent where present.    USE - The solid state p-n heterojunction is useful in optoelectronic devices including solar cell (photovoltaic cell) and photo-detector (light sensing device) (all claimed).    ADVANTAGE - The solid state p-n heterojunction: has high light gathering capacity over a broad spectrum; and provides optoelectronic devices having improved overall efficiency.    DETAILED DESCRIPTION - Solid state positive-negative (p-n) heterojunction comprises an organic p-type material in contact with an n-type material, where (i) the n-type material is surface-sensitized by at least two sensitizing agents comprising a donor sensitizing agent and an acceptor sensitizing agent and optionally at least one intermediate sensitizing agent, (ii) the emission spectrum of the donor sensitizing agent overlaps with the absorption spectrum of the acceptor sensitizing agent and/or with the absorption spectrum of at least one intermediate sensitizing agent where present, (iii) the emission spectrum of at least one intermediate sensitizing agent where present overlaps with the absorption spectrum of the acceptor sensitizing agent, and (iv) the acceptor sensitizing agent individually has a maximum absorbed photon to electron conversion efficiency of not less than 40% in an equivalent heterojunction when used as sole sensitizing agent. INDEPENDENT CLAIMS are also included for:    (1) use of at least two sensitizing agents comprising donor sensitizing agent and acceptor sensitizing agent and optionally at least one intermediate sensitizing agent, in the solid state p-n heterojunction; and    (2) manufacturing the solid state p-n heterojunction comprising: forming a layer (optimally porous layer) of n-type semiconductor material and surface sensitizing the layer simultaneously or sequentially with at least two sensitizing agents comprising donor sensitizing agent and acceptor sensitizing agent and optionally at least one intermediate sensitizing agent.