In order to better apply direct liquid-immersion cooling (LIC) method in temperature control of solar cells in high concentrating photovoltaic (CPV) systems, electrical characteristics of GaInP/GaInAs/Ge triple-junction solar cells immersed in dimethyl silicon oil of 1.0-30.0 mm thickness were studied experimentally under 500 suns and 25 degrees C. Theoretical photocurrent losses caused by spectrum transmittance decrease from spectral absorption of silicon oil were estimated for three series sub-cells, and an in-depth analysis of the electrical performances changes of the operated cell in silicon oil was performed. Compared with cell performances without liquid-immersion, the conversion efficiency and the maximum output power of the immersed solar cell in silicon oil of 1.0 mm thickness has increased from 39.567% and 19.556W to 40.572% and 20.083W respectively. However, the cell electrical performances decrease with increasing silicon oil thickness in the range of 1.0-30.0 mm, and the efficiency and the maximum output power of the cell have become less than those without liquid-immersion when the silicon oil thickness exceeds 6.3 mm. (C) 2015 Elsevier Ltd. All rights reserved.