The non-toxic nature and remarkable optoelectronic properties of kesterite (Cu₂ZnSnS₄ and CZTS) make CZTS a potential candidate for solar cell absorber layer material. Since alkali metal doping has shown a performance boost of active layers of solar cells, this work investigates the effects of significant lithium doping on sol-gel-produced CZTS thin films. CZTS- and lithium (Li)-doped CZTS thin films were prepared using the spin coating technique. The variation of structural, morphological, and optical properties of CZTS due to Li-doping has been studied by x-ray diffraction, scanning electron microscopy, and UV-visible spectroscopy techniques. All the synthesized Li_xCu_2-xZnSnS₄ (x = 0, 0.2, 0.4, 0.6) films showed fine crystallinity with average crystallite sizes of 4.745, 6.013, 6.255, and 6.404 nm, respectively. The average grain size decreases from 0.336 to 0.310 µm via increasing Li concentration. The inclusion of Li increased the bandgap energy ranges from 1.5 to 1.808 eV. The Li_0.6Cu_1.4ZnSnS₄ thin showed the highest absorption coefficient of 3.505 × 10⁴ cm^-1 among all the prepared thin films. A high optical conductivity over 10¹⁴ s^-1 was observed for CZTS, which further increased with an increased Li concentration. The synthesized structures showed enhanced characteristics suitable for solar cell application.