An apparatus for treatment of a cadmium telluride thin film photovoltaic device, the apparatus comprising: a treatment system comprising a preheating section, a treatment chamber, and an anneal oven, wherein the preheating section, the treatment chamber, and the anneal oven are separated from each other, and integrally interconnected, within the treatment system; and a conveyor system operably disposed within the treatment system and configured for transporting substrates in a serial arrangement into and through the preheat section, into and through the treatment chamber, and into and through the anneal oven at a controlled speed, and wherein: the treatment chamber is configured to heat the substrates with a cadmium telluride thin film thereon to a liquid treatment composition application temperature of about 50 °C to 125 °C and for applying a liquid treatment composition to the cadmium telluride thin film on the substrates at the liquid treatment composition application temperature; the liquid treatment composition comprises cadmium chloride; the liquid treatment composition is applied as one of i) a sprayed liquid treatment, or ii) a roll applicator liquid treatment; and the anneal oven is configured to heat the substrates with the cadmium telluride thin film thereon to an annealing temperature of from about 250 °C to about 500 °C as the substrates are continuously conveyed by the conveyor system through the treatment system, such that the cadmium telluride thin film on the substrates is doped with a material from the liquid treatment composition. a treatment system comprising a preheating section, a treatment chamber, and an anneal oven, wherein the preheating section, the treatment chamber, and the anneal oven are separated from each other, and integrally interconnected, within the treatment system; and a conveyor system operably disposed within the treatment system and configured for transporting substrates in a serial arrangement into and through the preheat section, into and through the treatment chamber, and into and through the anneal oven at a controlled speed, and wherein: the treatment chamber is configured to heat the substrates with a cadmium telluride thin film thereon to a liquid treatment composition application temperature of about 50 °C to 125 °C and for applying a liquid treatment composition to the cadmium telluride thin film on the substrates at the liquid treatment composition application temperature; the liquid treatment composition comprises cadmium chloride; the liquid treatment composition is applied as one of i) a sprayed liquid treatment, or ii) a roll applicator liquid treatment; and the anneal oven is configured to heat the substrates with the cadmium telluride thin film thereon to an annealing temperature of from about 250 °C to about 500 °C as the substrates are continuously conveyed by the conveyor system through the treatment system, such that the cadmium telluride thin film on the substrates is doped with a material from the liquid treatment composition. the treatment chamber is configured to heat the substrates with a cadmium telluride thin film thereon to a liquid treatment composition application temperature of about 50 °C to 125 °C and for applying a liquid treatment composition to the cadmium telluride thin film on the substrates at the liquid treatment composition application temperature; the liquid treatment composition comprises cadmium chloride; the liquid treatment composition is applied as one of i) a sprayed liquid treatment, or ii) a roll applicator liquid treatment; and the anneal oven is configured to heat the substrates with the cadmium telluride thin film thereon to an annealing temperature of from about 250 °C to about 500 °C as the substrates are continuously conveyed by the conveyor system through the treatment system, such that the cadmium telluride thin film on the substrates is doped with a material from the liquid treatment composition.