It is predicted that crystalline silicon passivated emitter and rear contact (c-Si PERC) solar cells will reach 70% global market share with the cell thickness decreased to 150 mm within next 7 years. It is of critical importance to address efficiency loss in order to deliver high cost-effective thinned Si cells. Herein, we not only address the efficiency loss but also acquire an extra gain for 150 mm-thick cells via optical and electrical designs. By rear design of SiNx/SiOx film, light absorption loss at longer wavelengths is made up. Via front design of SiO2/SiNx/SiOx film, light absorption at short wavelengths is enhanced and simultaneously, open circuit voltage (V-oc) is considerably improved. Compared with standard 180 mmthick cells, the present design experimentally lead to average short circuit current density (J(sc)) increase by 0.2 mA/cm(2) and average Voc improvement by 9 mV. Compared with standard thick cells and undesigned 150 mm-thick cells, net absolute efficiency gains are up to 0.4% from 22.0% to 22.4% and 0.6% from 21.8% to 22.4%, respectively. Device simulations are conducted to explain the experimentally observed improvements. The present study demonstrates a technical solution to address the efficiency loss in the thinned c-Si PERC cells. (C) 2020 Elsevier Ltd. All rights reserved.