NOVELTY - Organic photosensitive optoelectronic device comprises at least one donor-acceptor heterojunction formed from substituted squaraine compounds (I).    USE - The device is useful as solar cell or photodetector (claimed), or photoconductor cells, which are useful: to generate a usable electrical current from incident electromagnetic radiation (e.g. photovoltaic (PV) devices); or to detect incident electromagnetic radiation. Solar cells (PV devices) are useful to drive power consuming loads to provide e.g. lighting, heating, or to power electronic circuitry or devices comprising calculators, radios, computers and remote monitoring or communications equipment.    ADVANTAGE - The device has longer lifetime and diffusion length of triplet excitons in comparison to singlet excitons allow for the use of a thicker photoactive region, as the triplet excitons may diffuse a greater distance to reach the donor-acceptor heterojunction, without sacrificing device efficiency. The device has: reduced series resistance; improved fabrication yield; optimized external quantum efficiency to maximize the sensitivity to desired spectral regions; and structural designs that enhance the photoconversion efficiency by optimizing the optical geometry for high absorption and for use with optical concentrators that increase collection efficiency, where such geometries increases the optical path through the material by trapping the incident radiation within a reflective cavity or waveguiding structure. The device recycles the light by multiple reflection through the photoresponsive material.    DETAILED DESCRIPTION - Organic photosensitive optoelectronic device comprises at least one donor-acceptor heterojunction formed from substituted squaraine compounds of formula (I).    Ar1, Ar2 = optionally substituted aromatic group.    An INDEPENDENT CLAIM is also included for a method of forming the organic photosensitive optoelectronic device, comprising forming at least one donor-acceptor heterojunction by depositing (I) on a substrate (110).    DESCRIPTION OF DRAWING(S) - The figure shows the illustrative diagram of an organic photovoltaic device.    Substrate (110)    Anode (115)    Donor layer (125)    Acceptor layer (130)    Cathode (140)