High-quality passivation and transport from doped nano-crystalline silicon-oxide layers
In the 4th work package of NextBase project, TUDelft develops doped nano-crystalline silicon-oxide (nc-SiOx: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-SiOx:H layers are excellent candidates as emitter and BSF fingers in NexBase IBC solar cells.
TUDelft n-type and p-type nc-SiOx: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-SiOx: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 35th EU PVSEC . In the framework of NextBase project, these doped nc-SiOx: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.
 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-SiOx:H layers, 35th European PV Solar Energy Conference and Exhibition, Brussels, Belgium (2018).