High efficiency n-type silicon solar cells featuring passivated contact to laser doped regions

Minimizing carrier recombination at cell contacts becomes increasingly important for reaching high efficiency. In this work, the passivated contact concept is implemented into n-type silicon solar cells with laser-processed local back surface fields. The passivation and contact characteristics of the SiO2/amorphous silicon (a-Si:H) stack on localized laser doped n+ regions are investigated. We find that the SiO2/a-Si:H stack provides not only good passivation to laser doped n+ regions but also allows a low contact resistivity after thermal annealing. With the implementation of the SiO2/a-Si:H passivated contact, an absolute efficiency gain of up to 1.5% is achieved for n-type solar cells

Silicon heterojunction solar cells with electron selective TiOx contact

Silicon solar cells featuring carrier selective contacts have been demonstrated to reach ultra-high conversion efficiency. In this work, the electron-selective contact characteristics of ultrathin TiOx films deposited by atomic layer deposition on silicon are investigated via simultaneous consideration of the surface passivation quality and the contact resistivity. Thin TiOx films are demonstrated to provide not only good passivation to silicon surfaces, but also allow a relative low contact resistivity at the TiOx/Si heterojunction. A maximum implied open-circuit voltage (iVoc) of ~703 mV is achieved with the passivation of a 4.5 nm TiOx film, and a relatively low contact resistivity of (~0.25 Ω cm2 is obtained at the TiOx/n-Si heterojunction simultaneously. N-type silicon solar cell with the champion efficiency of 20.5% is achieved by the implementation of a full-area electron-selective TiOx contacts. A simulated efficiency of up to 23.7% is achieved on the n-type solar cell with a full-area TiOx contact. The efficient, low cost electron-transporting/hole-blocking TiOx layer enables the fabrication of high efficiency silicon solar cells with a simplified process flow

Passivated contacts to laser doped p+ and n+ regions

In this work, tunnel SiO2/a-Si:H stacks are trialed as passivated contacts to laser doped pþ and nþ regions. The passivation performance and contact resistivity are investigated as a function of the tunnel SiO2 thickness and annealing condition. We find that the SiO2/a-Si:H stack provides excellent passivation to laser doped nþ regions, with corresponding low recombination current density (Jo) values. A lower level of surface passivation is achieved by the SiO2/a-Si:H stack on laser doped pþ regions. A postdeposition forming gas anneal (FGA) at 400 °C is found to improve the passivation performance to laser doped pþ regions and deteriorate the passivation to laser doped nþ regions. Acceptable contact resistivity (ρc) values have been obtained for both laser doped nþ and pþ regions after aluminum metallization and a post FGA to activate the alloying process between the a-Si:H and aluminum layer. In the final part of this work implementation of the passivated contacts to laser doped regions into a simplified interdigitated back-contact (IBC) solar cell fabrication process is proposed. Simulation result suggests that IBC device with an efficiency of up to 23% can be achieved using the obtained experimental results

Boron implanted, laser annealed p+ emitter for n-type interdigitated back-contact solar cells

Ion implantation and laser processing technologies are very attractive for the fabrication of industrially feasible interdigitated back-contact (IBC) solar cells. In this work, p+ emitters were fabricated by boron implantation and laser annealing, and the electrical properties of emitters were investigated. An emitter sheet resistance (Rsh) in the range of 30-200 Ω/ could be achieved by varying the implanted dose. The saturation current density (Joe) of the passivated p+ emitter with Rsh of ∼ 125 Ω/ reached 95 fA/cm2, and the contact resistivity was determined to be as low as 5 × 10-6 Ω cm2. Such localized p+ emitters can be applied to ntype IBC solar cells, which could avoid the high temperature thermal annealing step and related problems