An investigation of low temperature MBE growth of crystalline Cd(1-x)Zn(X)Te with 0 <= x <= 1, in the range 220 degrees C <= T-s <= 320 degrees C, and extrinsic doping is conducted. This results in the construction of homo-junction crystalline solar cells on lattice-mismatched 211B and 111B GaAs substrates. Doping and composition studies of crystalline layers are used as a guide for low-temperature, high growth-rate, MBE grown polycrystalline CdTe solar cells on various n-type emitters and different back-contacts. The best resulting devices reach efficiencies of 14.7% under AM 1.5 g, without an anti-reflection coating.