The Indium Gallium Nitride III-N alloy has the required potentialities to be a material of choice used in the next generation high efficiency solar cells. Indeed, the mere change in its Indium composition allows its absorption to cover the whole solar spectrum. One of InGaN main challenges remains today its p-doping. We therefore propose a comparative study between PN and PIN thin films structures, alongside new Schottky based designs which allow the removal of the difficult p-layer. A mathematically rigorous multi-criteria structure optimization associated to a 2D simulation based on actually measured physical parameters and precise models lead to theoretical efficiencies of 17.8%, 19.0%, 18.2% and 19.8% respectively for the PN, PIN, Schottky and a new proposed Metal-IN (MIN) Schottky based structure. The tolerance that is allowed on each parameter for each of the proposed cells has been thoroughly studied. These studies have shown that the new MIN structure exhibits high fabrication tolerances. This is particularly true for the n-doping of its n-layer, which can be raised enough, without loss of efficiency, to realize good low resistance ohmic contacts. Therefore, these new InGaN Schottky Based Solar Cells (SBSC) are shown to be efficient and tolerant alternatives to the conventional structures, allowing the removal of the p-type doping of InGaN while giving photovoltaic (PV) performances comparable to the highest reported thin films Solar Cell efficiencies.