NOVELTY - The process for making a thin film solar cell on a substrate (10), comprises depositing a series of inks comprising organic solvent onto the conducting substrate coated with an electrical contact layer in sequence, depositing a chalcogen layer on the substrate, optionally selenizing or sulfurizing the layered substrate, and heating each ink layer at 300-650 degrees C to convert the ink to a material before depositing the next ink layer thus forming a final material layer on the substrate having a concentration gradient for metal atoms.    USE - The process is useful for making a thin film solar cell on a substrate, where the solar cell is useful for rooftops and sunlighted surfaces and roofing materials such as roofing tiles or shingles.    ADVANTAGE - The process is capable of simply making the thin film solar cell in an environmentally friendly manner with high light conversion efficiency and purity and without any structural defects.    DETAILED DESCRIPTION - The process for making a thin film solar cell on a substrate (10), comprises depositing a series of inks comprising organic solvent onto the conducting substrate coated with an electrical contact layer in sequence, depositing a chalcogen layer on the substrate, optionally selenizing or sulfurizing the layered substrate, and heating each ink layer at 300-650 degrees C to convert the ink to a material before depositing the next ink layer thus forming a final material layer on the substrate having a concentration gradient for metal atoms, where each ink in the sequence contains a polymeric precursor compound of a different stoichiometry from the other inks. The sequence of inks has a step or continuous gradient in the stoichiometry of the metal atoms. The solar cell has a gradient of the concentration of: copper atoms in a photovoltaic absorber layer (30), where the gradient is a higher concentration of copper atoms at the back of the photovoltaic absorber layer to a lower concentration of copper atoms at the front of the photovoltaic absorber layer; atoms of M(B) in the photovoltaic absorber layer, where the gradient is a lower concentration of atoms of M(B) at the back of the photovoltaic absorber layer to a higher concentration of atoms of M(B) at the front of the photovoltaic absorber layer or is a higher concentration of atoms of M(B) at the front and back of the photovoltaic absorber compared to the concentration of atoms of M(B) in the middle of the photovoltaic absorber layer and M(B) is indium, gallium or aluminum; sodium atoms in the photovoltaic absorber layer, where the gradient is a higher concentration of sodium atoms at the back of the photovoltaic absorber layer to a lower concentration of sodium atoms at the front of the photovoltaic absorber layer or is a lower concentration of sodium atoms at the back of the photovoltaic absorber layer to a higher concentration of sodium atoms at the front of the photovoltaic absorber layer. The final material layer is a photovoltaic absorber material layer. The deposition step is carried out by spraying, spray coating, spray deposition, spray pyrolysis, printing, screen printing, inkjet printing, aerosol jet printing, ink printing, jet printing, stamp printing, transfer printing, pad printing, flexographic printing, gravure printing, contact printing, reverse printing, thermal printing, lithography, electrophotographic printing, electrodepositing, electroplating, electroless plating, bath deposition, coating, wet coating, dip coating spin coating, knife coating, roller coating, rod coating, slot die coating, meyer bar coating, lip direct coating, capillary coating, liquid deposition, solution deposition, layer-by-layer deposition, spin casting, and/or solution casting.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of a solar cell.    Substrate (10)    Electrode layer (20)    Absorber layer (30)    Buffer layer (40)    Transparent conductive layer. (50)