NOVELTY - Forming absorber layer (306) containing elements of groups IB, IIIA and VIA involves atomic monolayer resolution tuning of a bandgap grading of a precursor layer on substrate (302), where the tuning occurs with spatial uniformity and resolution through deposition of partial atomic monolayers with aggregate growth rate directly proportional to number of reaction cycles, where after exposure to precursor agent and then reducing agent, atoms from each of partial atomic monolayers occupy only portion of all deposition sites on target surface; and repeating atomic monolayer deposition.    USE - For forming absorber layer used for fabricating solar cells, and optoelectronic device e.g. photovoltaic cell.    ADVANTAGE - The method enables low cost production of solar cells on flexible substrates using printing or web coating technologies is promising highly cost-efficient alternative to traditional silicon-based solar cells. By use of atomic layer deposition (ALD), copper, indium, gallium, and selenium can be deposited in a precise stoichiometric ratio that is intermixed at or near the atomic level. Furthermore, by changing sequence of exposure pulses for each precursor material, the relative composition of copper, indium, gallium and selenide within each atomic layer can be systematically varied as a function of deposition cycle and thus depth with the product deposit. Both of these features can provide benefits (such as improved power conversion efficiency) as the product deposited serves within the absorber layer of a solar cell. These benefits are much more difficult to achieve with conventional co-evaporation, sputtering, or solution-based deposition of inorganic materials used for the absorber layers of solar cells, as both the spatial uniformity and the potential resolution of atomically-graded deposition profiles of these processes is considerably less than for ALD-based deposition. Further, the reproducibility of non-ALD-based processes is less than that of ALD-based deposition.    DETAILED DESCRIPTION - Forming absorber layer (306) containing elements of groups IB, IIIA and VIA involves atomic monolayer resolution tuning of a bandgap grading of a precursor layer on substrate (302), where the tuning occurs with spatial uniformity and resolution through deposition of partial atomic monolayers with aggregate growth rate directly proportional to a number of reaction cycles rather than pressure or concentration of precursor gases in the chamber, with control over film thickness, film uniformity, and conformality; where after exposure to a precursor agent and then reducing agent, atoms from each of the partial atomic monolayers occupy only a portion of all deposition sites on a target surface; repeating atomic monolayer deposition until a desired atomically-graded deposition profile is formed in the precursor layer.    DESCRIPTION OF DRAWING(S) - The figure shows schematic view of photovoltaic cell.    Base layer (302)    Base electrode (304)    Absorber layer (306)    Window layer (308)    Transparent electrode (310)