High efficiency (>22%) Si-solar cells with optimized emitter

A systematic experimental study is presented that aims at the optimization of the emitter of high-efficiency Si-solar cells. The emitter is processed by a homogeneous weak n⁺ diffusion and an additional local deep n⁺⁺ diffusion under the front grid. Solar cells and dark saturation current test structures with different homogeneous emitter sheet resistivities varying between 40 Ω/sq. and 300 Ω/sq. and with different junction depths have been processed. In addition the junction depth and the sheet resistivity of the local n⁺⁺ emitter was varied for each set of homogeneous emitter. As a further variation the phosphorous deep diffusion of the local emitter was either performed together with the deep diffusion of the homogeneous n⁺ emitter or with an additional step before the n⁺-doping. The test structures and solar cells were analyzed by various techniques (doping profile, dark saturation current, photoconductance decay, solar cell parameters). With the optimized parameters for our solar cells efficiencies up to 22.3% (AM1.5) have been achieved on FZ-silicon and 21.3% on Cz-silicon. The Cz-Si result is, to our knowledge, a record value