  We predict a formation of intravalley and intervalley controllable trions in
buckled 2D materials such as silicene, germanene and stanene monolayers in an
external electric field. A study is performed within the framework of a
nonrelativistic potential model using the method of hyperspherical harmonics
(HH). We solve the three-body Schr\"{o}dinger equation with the Rytova-Keldysh
potential by expanding the wave functions of a trion in terms of the HH. A
resultant system of coupled differential equations are solved numerically.
Controllable ground state energies of intravalley and intervalley trions by the
external electric field are presented. The dependencies of the binding energy
(BE) of trions in the silicene, germanene and stanene as a function of the
electric field are qualitatively similar. BEs of trions formed by $A$ and $B$
excitons have a non-negligible differences which slightly increase as the
electric field increases. It is demonstrated that trion BEs can be controlled
by the external electric field and the dielectric environment has a significant
effect on the trion BE
