NOVELTY - Aluminum paste composition comprises (in wt.%): crystalline calcium oxide (0.03-9); an aluminum powder (27-89.9), where the weight ratio of aluminum powder to crystalline calcium oxide is 9:1-1000:1; and an organic vehicle (10-70).    USE - The aluminum paste composition is useful for forming an aluminum back electrode of a solar cell, including silicon solar cell (all claimed), photodiodes, and semiconductor devices.    ADVANTAGE - The aluminum paste composition provides a solar cell: with improved energy conversion efficiency; and exhibiting reduction in cell bowing without impacting the cell efficiency and adhesion, as compared to solar cells formed using aluminum paste without any crystalline calcium oxide.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for:    (1) a solar cell (400) comprising: a positive-type silicon substrate comprising a positive-type region (410) sandwiched between an negative-type region (420) and a back surface field layer, where the back surface field layer comprises crystalline calcium oxide and aluminum; an aluminum back electrode (461) disposed on the back surface field layer, where the aluminum back electrode comprises 0.1-10 wt.% of crystalline calcium oxide and 90-99.9 wt.% of aluminum; and a metal front electrode (451) disposed over a portion of the negative-type region;    (2) forming a silicon solar cell, comprising: (a) applying the aluminum paste composition on a backside of a positive-type silicon substrate; (b) applying a metal paste on a front-side of the positive-type silicon substrate, where the front-side is opposite to the back-side; (c) firing the positive-type silicon substrate after the application of the aluminum paste at a peak temperature of 600-950 degrees C; and (d) firing the positive-type silicon substrate after the application of the metal paste on the front side at a peak temperature of 600-950 degrees C; and    (3) the silicon solar cell made by the process.    DESCRIPTION OF DRAWING(S) - The figure shows a cross-sectional view of the solar cell.    Solar cell (400)    Positive-type region (410)    Negative type region (420)    Metal front electrode (451)    Aluminum back electrode (461)