NOVELTY - The solar cell comprises alloyed semiconductor nanocrystals having a light absorbing volume, a donor absorption region, and an acceptor absorption region. The absorption region comprises a host material and a dopant material. The dopant materials absorb an incident photon to create a singlet exciton (1). The host materials absorb a virtual photon to create a triplet exciton. The triplet exciton is transported within the absorption region. The host material comprises organic materials. The acceptor region contacts the donor region to form a donor-acceptor heterojunction (3).    USE - Used as a solar cell e.g. organic-based photovoltaic cell.    ADVANTAGE - The solar cell has improved potential to provide very low cost solar energy conversion, and is easy for processing and compatible with flexible substrates.    DETAILED DESCRIPTION - The solar cell comprises alloyed semiconductor nanocrystals having a light absorbing volume, a donor absorption region, and an acceptor absorption region. The absorption region comprises a host material and a dopant material. The dopant materials absorb an incident photon to create a singlet exciton (1). The host materials absorb a virtual photon to create a triplet exciton. The triplet exciton is transported within the absorption region. The host material comprises organic materials. The acceptor region contacts the donor region to form a donor-acceptor heterojunction (3), where the triplet exciton is transported within the donor region to the donor-acceptor heterojunction and creates a first and a second charge at the donor-acceptor heterojunction. The second charge is transported away from the donor-acceptor heterojunction in the donor region. The alloyed semiconductor nanocrystal composition, the nanocrystal size and the nanocrystal distribution are selected to achieve a desired band gap and electron affinity. The ternary semiconductor alloy comprises the ternary semiconductor alloy of (ZnxCd1-xse), (CdSeyTe1-y), (PbxCd1-xSe), (InxGa1xAs) and InAs1yPy, and quaternary semiconductor alloy of (Cu(InxGa1-x)Se2), Cu(InxGa1-x)Se2 and Cu(InxAl1-x)Se2, where x is less than 0 and y is less than 1.    DESCRIPTION OF DRAWING(S) - The diagram shows an energy level of an organic photovoltaic cell.    Singlet exciton (1)    Triplet excited state (2)    Donor-acceptor heterojunction. (3)