Large area 19.4% efficient rear passivated silicon solar cells with local Al BSF and screen-printed contacts

Abstract

Summary form only given. This paper describes the cell design and technology for achieving 19.4% efficient cells on large-area (239 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) commercial grade Cz Si wafers using industrially feasible oxide/SiNx rear passivation and screen-printed local back contacts. A combination of optimized front and back dielectrics, rear surface finish, oxide thickness and fixed oxide charge and interface quality provided effective surface passivation without parasitic shunting. Increasing the rear oxide thickness from 40 Å to 90 Å in conjunction with reducing the surface roughness from 5 mm to 0.2 mm increased the V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oc</sub> by 16 mV to 656 mV, J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sc</sub> was 38.1 mA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and FF was 0.778 for the 19.4% cell, which is the highest efficiency 239 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> fully screen-printed Cz cell. Compared to 18.6% full Al-BSF reference cell, LBSF improved the BSR from 71% to 95% and lowered the BSRV from 310 to 130 cm/s. 2D computer simulations were performed to optimize the size, shape and spacing of local BSF regions to obtain good FF. Model calculations show that 20% efficiency cells can be achieved with further optimization of local Al-BSF cell structure and improved screen-printed contacts.