Application of PCBM Layer as a Back Reflector of Micromorph Tandem Silicon Solar Cells

We analyzed the effect of using PCBM layers as back reflector of tandem amorphous silicon solar cells. The new possibility of using polymer materials as a back reflector of inorganic silicon based solar cells was discussed. By applying the PCBM back reflector, short circuit current density increased from 9.83 mA/cm(2) to 11.7 mA/cm(2) with proper interface treatment. In order to obtain the tandem cell with high fill factor, HF treatment is required before depositing PCBM on n-mu c-Si:H. Series resistance can significantly be increased by little amount of native oxide. Comparison between the reference cell without back reflector and thickness optimized PCBM cell indicated a decrease in open circuit voltage from 1.41 to 1.29 V. These results implied that further optimization of electrical properties, such as electrical conductivity and activation energy is required to minimize the drop in terms of open circuit voltage and fill factor.