Conductivity and Surface Passivation Properties of Boron‐Doped Poly‐Silicon Passivated Contacts for c‐Si Solar Cells

Abstract

Passivating the contacts of crystalline silicon (c‐Si) solar cells with a poly‐crystalline silicon (poly Si) layer on top of a thin silicon oxide (SiOx) film are currently of growing interest to reduce recombination at the interface between the metal electrode and the c‐Si substrate. This study focuses on the development of boron‐doped poly‐Si/SiOx structure to obtain a hole selective passivated contact with a reduced recombination current density and a high photo‐voltage potential. The poly‐Si layer is obtained by depositing a hydrogen‐rich amorphous silicon layer by plasma enhanced chemical vapor deposition (PECVD) exposed then to an annealing step. Using the PECVD route enables to single side deposit the poly Si layer, however, a blistering of the layer appears due to its high hydrogen content, which leads to the degradation of the poly‐Si layer after annealing. In this study, the deposition temperature and gas flow ratio used during PECVD step are optimized to obtain blister‐free poly‐Si layer. The stability of the surface passivation properties over time is shown to depend on the blister density. The surface passivation properties are further improved thanks to a post process hydrogenation step. As a result, a mean implied photo‐voltage value of 714 mV is obtained.

Role of silicon surface, polished 〈100〉 and 〈111〉 or textured, on the efficiency of double‐sided TOPCon solar cells

“…The temperature ramps are set as low as 100 C/h for both the annealing and cooling down to prevent blistering effect on surface. 28,29 The doping concentration and the junction depth of the boron and hydrogen atoms from the front (p) stack are confirmed by SIMS measurements. Besides, the oxygen, carbon, and nitrogen concentrations are also analyzed.…”

Firing stability of tube furnace‐annealed n‐type poly‐Si on oxide junctions

“…Therefore, it is reasonable to assume that on the one hand, hydrogen passivates interface defects resulting from the thermal stress at the interface during firing as can be seen on samples fired without a hydrogen‐containing capping layer, but on the other hand, a hydrogen concentration that is too high at the interface might also lead to cracks or blisters in the overlying layers. The phenomenon of blistering in poly‐Si contacts is well known and occurs in particular during annealing of in situ doped PECVD poly‐Si layers and was attributed to hydrogen in the layers 57–59 . A detailed explanation of the effect is not yet known, but there are suggestions such as detachment of the entire layer from the underlying interfacial oxide due to stresses at the interface, while hydrogen accumulates in the resulting cavity and thus increases the internal pressure 60 .…”

“…The phenomenon of blistering in poly-Si contacts is well known and occurs in particular during annealing of in situ doped PECVD poly-Si layers and was attributed to hydrogen in the layers. [57][58][59] A detailed explanation of the effect is not yet known, but there are suggestions such as detachment of the entire layer from the underlying interfacial oxide due to stresses at the interface, while hydrogen accumulates in the resulting cavity and thus increases the internal pressure. 60 Furthermore, it was shown that blistering is directly related to the interfacial oxides.…”

SiOxNy:B layers for ex-situ doping of hole-selective poly silicon contacts: A passivation study

“…In-situ B-doped a-Si:H layer were previously developed in our lab by PECVD. The use of a high deposition temperature (T dep = 300°C) and a high gas ratio (R = H 2 /SiH 4 = 50) afforded blister-free passivating poly-Si(B)/SiO x structures after annealing 4 . The use of a high gas ratio R during PECVD could promote a deposition of microcrystalline Si layers (μc-Si) 8 .…”

“…Poly-Si(B) layers are prepared by Plasma-Enhanced Chemical Vapor Deposition (PECVD) of an amorphous silicon (a-Si:H) layer followed by a crystallization annealing step. Poly-Si(B) layers were previously developed in our lab by in-situ doping the a-Si:H layer with the addition of B 2 H 6 to the precursor gas mix 4 . However, the use of H-rich precursor gases during the PECVD step is leading to a blistering phenomenon of the layer 5,6 .…”