Fabrication of 20 % efficient cells using spin-on based simultaneous diffusion and dielectric anneal

Low-cost high efficiency solar cells are the key to achieving grid parity with photovoltaic devices. This paper details the fabrication, characterization and analysis of 4 cm² screen printed cells with efficiency over 20% achieved using a local back surface field cell structure in conjunction with a 75 ohm/sq emitter and efficient back surface reflector. A streamlined process sequence involving a single high temperature step for simultaneous formation of emitter and rear passivation was used. The combination of LBSF and improved rear reflector resulted in a peak efficiency of 20.1% with J_SC of 39.4 mA/cm² and V_OC of 652 mV. Detailed characterization and modeling involving IQE and escape reflectance measurements revealed that the increase in V_OC and J_SC was the result of increased BSR from 67% to 93% and reduced BSRV from 325 cm/s to 125 cm/s. Improved rear passivation was found to be an effective method for controlling charge-induced inversion or parasitic shunting at the rear surface. Future experiments and further optimization are expected to result in efficiencies of over 20% on thin wafers using a similar cell structure.