high the cost to grow the thin film up to a thickness sufficient to obviate the reliability hazard may very well exceed the high cost of the substrate negating what savings were to be realized by using the epitaxial liftoff in the first place another problem of the current epitaxial liftoff technology is increasing energy conversion efficiency to obtain high energy conversion efficiency it is desirable that the sensitivity of the solar cell thin film 39 s iii v materials cover the whole solar spectrum there are iii v materials whose sensitivity extends to cover the low frequency side of the solar spectrum as well however the materials that provide sufficient low frequency coverage of the solar spectrum tend to have larger lattice constants than that of a gaas substrate to grow such lattice mismatched materials on the gaas substrate a thick buffer layer would be required even then high reliability would be difficult to obtain a thick buffer layer increases overall cell cost and tends to be prohibitive for most epitaxial liftoff applications gains in the energy conversion efficiency using this approach are also limited because the number of lattice mismatched layers that can actually be inserted in the solar cell structure is limited epitaxial liftoff is very attractive technology to reduce iii v solar cell production costs however as mentioned above reliability issues persist and potential increases in the energy conversion efficiency remain limited growth of thick iii v film to improve reliability unduly increases production costs and makes it difficult to justify using the.