It's expensive to manufacture silicon at semiconductor quality, even when talking about polycrystalline wafers. (Monocrystalline wafers, used for "chips", is even more expensive and prone to defect." People are increasing production of polycrystalline silicon wafers but the demand is much greater than the supply, even with this increase. The cycle basically goes like this: polycrystalline gets more expensive because of demand -> supply increases -> prices go down (in theory) -> demand increases -> polycrystalline gets expensive again.

This is an endless loop right now, as the total amount of possible demand is >> than the growth of polycrystalline foundries. Furthermore, LCD displays also use this form of polycrystalline silicon, which doesn't help with the demand problem. Decently-graded silicon is inherently expensive to manufacture because of the process involved.

The takeaway is that if these metal-oxides are cheaper to produce, even if they are more expensive for the raw material, the cost savings would carry over to the products. Equally relevant when talking about solar cells is how much energy is needed to produce the cells themselves. Right now, an enormous amount of energy is required for silicon solar cells. Helping the energy crisis doesn't help if something takes that much energy to produce. (I do not know the ratio of lifetime energy output versus energy to manufacture but I am sure it's not very good.)