  The Dieudonn\'e crystal of a p-divisible group over a semiperfect ring R can
be endowed with a window structure. If R satisfies a boundedness condition,
this construction gives an equivalence of categories. As an application one
obtains a classification of p-divisible groups and commutative finite locally
free p-group schemes over perfectoid rings by Breuil-Kisin-Fargues modules if
p>2.
