NOVELTY - The photovoltaic cell useful in photovoltaic device, comprises group IV-VI semiconductor nanocrystals as photoactive components, where the nanocrystals are: core-shell semiconductor nanocrystals each comprising a core of a first group IV-VI semiconductor material having a selected band gap energy and a core-overcoating shell consisting of a second group IV-VI semiconductor material; or core-alloyed shell semiconductor nanocrystals each comprising a core of a first group IV-VI semiconductor material having a selected band gap energy and a core-overcoating alloyed shell.    USE - The photovoltaic cell is useful in a photovoltaic device (claimed).    ADVANTAGE - The photovoltaic cell has high photovoltaic efficiency, provides gradual change of the dielectric constant using the alloyed shell of the semiconductor nanocrystals thus improving the internal quantum yield by decreasing carriers such as electrons or holes trapping probability in an abrupt core-shell interface, and enables efficient generation of electron-hole pairs and immediate charge separation.    DETAILED DESCRIPTION - The photovoltaic cell useful in photovoltaic device, comprises group IV-VI semiconductor nanocrystals as photoactive components, where the nanocrystals are: core-shell semiconductor nanocrystals each comprising a core of a first group IV-VI semiconductor material having a selected band gap energy and a core-overcoating shell consisting of a second group IV-VI semiconductor material; or core-alloyed shell semiconductor nanocrystals each comprising a core of a first group IV-VI semiconductor material having a selected band gap energy and a core-overcoating alloyed shell consisting of an alloy of the first and second group IV-VI semiconductor material. The nanocrystals are present in the form of spheroids or rods. The core and the core-overcoating shell, if present, have the structure of AB or AC, and the core-overcoating alloyed shell, if present, consists of an alloy of the ABxC1-x structure, where A is lead, B and C are sulfur, selenium or tellurium, x is the mole fraction of B, 1-x is the mole fraction of C and x is 0-1. The band gap energy of the core semiconductor material is present in the infrared range. If the nanocrystals are core-shell semiconductor nanocrystals, then the core semiconductor material is lead selenide and the core-overcoating shell is made of lead sulfide, or if the nanocrystals are core-alloyed shell semiconductor nanocrystals, then the core semiconductor material is lead selenide, and the core-overcoating alloyed shell has the PbSexS1-x structure, where x is the mole fraction of selenium, 1-x is the mole fraction of sulfur and x is 0-1. The alloyed shell exhibits gradual change of the crystallographic lattice spacing and/or gradual change of the dielectric constant. The nanocrystals have a size of 2-20 nm. The nanocrystals: have a tunable single exciton absorption in the spectral range of 800-3500 nm; have an impact ionization process excited in the ultraviolet and visible spectral regime that leads to multiple carrier generation thus enabling absorption processes that cover a wide spectral range; have an efficient internal charge carrier separation; exhibit less than 5% root-mean-square deviation in diameter; exhibit photoluminescence having quantum yields greater than 80%; are packed as a single layer thin film sandwiched between collecting electrodes and acting as an insolating layer in a p-i-n configuration, where an internal charge separation in each one of the nanocrystals allows the migration of a charge carrier to a relevant collecting electrode; are packed as a bi-layer hetero-junction comprising a layer of nanocrystals in conjunction with a second layer of nanocrystals or a conductive polymer film having a staggered energy band alignment that facilitate a charge transfer of a donor-acceptor pair, which is sandwiched between collecting electrodes; are packed as a single layer of a nanocrystal-conductive polymer blend having a staggered energy band alignment that facilitates a charge transfer of a donor-acceptor pair, which is sandwiched between collecting electrodes and permits an excess charge separation and a charge carrier diffusion to a relevant collecting electrode; are packed as a single layer of nanocrystals deposited onto a titanium dioxide particle film; and act as photo-sensitizers, injecting their electrons into the titanium dioxide film. An INDEPENDENT CLAIM is included for a photovoltaic device comprising a photovoltaic cell and a photonic structure that acts as a fluorescence collector.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic drawing of a photovoltaic cell.