High-quality passivation and transport from doped nano-crystalline silicon-oxide layers

In the 4^th work package of NextBase project, TUDelft develops doped nano-crystalline silicon-oxide (nc-SiO_x:H) layers to be implemented as emitter and back surface field (BSF) fingers in c-Si IBC heterojunction solar cells. Alloying nc-Si:H with oxygen during plasma deposition widens the bandgap of the material up to 2.7 eV for n-type doping and 2.27 eV for p-type doping. Moreover, its nano-crystalline nature allows to reach activation energy as low as 40.5 meV in case of n-type doping and 99 meV in case of p-type doping. Successfully combining large bandgap and low activation energy means extra-transparent thin films that concurrently facilitate carriers transport. In other words, TUDelft doped nc-SiO_x:H layers are excellent candidates as emitter and BSF fingers in NexBase IBC solar cells.

Schematic cross-section of the front/back contacted solar cell precursor used for the passivation test.

TUDelft n-type and p-type nc-SiO_x:H layers boost also surface passivation when deposited on hydrogenated intrinsic amorphous silicon (i-a-Si:H) passivating layers, that sandwich a double-side textured 280-μm thick n-type c-Si wafer. Further, covering front and back sides with sputtered ITO conductive transparent oxide (see figure above), TUDelft doped nc-SiO_x:H layers are found to prevent the worsening of surface passivation induced by sputtering (see table below). These results and further developments will be reported by TUDelft at the 35^th EU PVSEC [1]. In the framework of NextBase project, these doped nc-SiO_x:H layers will be gradually rolled out in flow-charts for fabricating c-Si IBC heterojunction solar cells at both TUDelft and NextBase partners’ locations.

[1] Engin Özkol, Yifeng Zhao, Gerwin Remon van Kuler, Paul Procel, Guangtao Yang, Gianluca Limodio, Arthur Weeber, Olindo Isabella, Miro Zeman, Recent progress in front/back contacted c-Si heterojunction solar cells using nc-SiO_x:H layers, 35^th European PV Solar Energy Conference and Exhibition, Brussels, Belgium (2018).