First-order formalism for dark energy and dust
  This work deals with first-order formalism for dark energy and dust in standard cosmology, for models described by real scalar field in the presence of dust in spatially flat space. The field dynamics may be standard or tachyonic, and we show how the equations of motion can be solved by first-order differential equations. We investigate a model to illustrate how the dustlike matter may affect the cosmic evolution using this framework. 
D. Bazeia, L. Losano, J. J. Rodrigues, R. Rosenfeld