Window layer with p doped silicon oxide for high Voc thin-film silicon n-i-p solar cells

Abstract

We investigate the influence of the oxygen content in boron-doped nanocrystalline silicon oxide films (p-nc-SiOx) and introduce this material as window layer in n-i-p solar cells. The dependence of both, optical and electrical properties on the oxygen content is consistent with a bi-phase model which describes the p-nc-SiOx material as a mixture of an oxygen-rich (O-rich) phase and a silicon-rich (Si-rich) phase. We observe that increasing the oxygen content enhances the optical gap E04 while deteriorating the activation energy and the planar conductivity. These trends are ascribed to a higher volume fraction of the O-rich phase. Incorporated into n-i-p a-Si:H cells, p-nc-SiOx layers with moderate oxygen content yield open circuit voltage (Voc) up to 945 mV, which corresponds to a relative gain of 11% compared to an oxygen-free p-layer. As a similar gain is obtained on planar and on textured substrates, we attribute the increase in Voc to the higher work function of the p-nc-SiOx layer made possible by its wider band gap. These results are attained without changing the dilution ratio of the 250 nm thick intrinsic layer. We also observe an enhancement of 0.6 mA cm−2 in short circuit current density in the short wavelengths due to the higher transparency of the p-nc-SiOx layer. Finally, an initial efficiency of 9.9% for a single junction 250 nm a-Si:H n-i-p solar cell on plastic foil is achieved with the optimization of the p layer thickness, the doping ratio of the front transparent conductive oxide, and the optical properties of the back reflector.

Nanopyramid Structure for Ultrathin c-Si Tandem Solar Cells

“…So the insertion of the n-SiOx results in the improvement of the intrinsic material properties, and the introduction of the p-SiO x only contributes to the interface improvement, which is consist with the recent result. 27 As we know SiO x is a mixed-phased nanomaterial consisting of nanometer silicon wire embedded in silicon oxide phase, 28 it has a strong electrical anisotropy that the transverse conductivity is expected to be larger than the lateral conductivity; the low lateral conductivity helps to quench the undesired local current drains at the interface or in the intrinsic layer, while the high transverse conductivity maintains the low series resistance. 29 The absolute increase in V oc and J sc lead to a dramatic improvement of the tandem cell efficiency.…”

Origin of the Voc enhancement with a p-doped nc-SiOx:H window layer in n-i-p solar cells

“…In the latter case, Cuony et al [9] attribute this improvement to the shunt quenching effect but it appears that it is not the dominant effect in the case of a-Si:H n-ip solar cells as reported by Biron et al [11]. Other groups reported that SiOx:H layers fabricated by glow discharge deposition from a SiH 4 -CO 2 -H 2 precursor gas mixture lead to the formation of a mixed phase (MP) material in which silicon nanocrystals are embedded into an a-SiOx:H matrix [12,13], instead of an amorphous Si-O compound corresponding to the random network model (RNM) [14,15].…”

“…In Fig. 3, the experimental V oc trend of our previous contribution is included [11]. The error in the V oc measurements shown in this contribution is ±5 mV due to the uncertainty of the substrate temperature.…”

“…The solar cell fabrication and layer characterization were the same as in a previous publication [11]. The p-nc-SiO x reference layers were deposited on glass by very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD) at 70 mHz and 0.4 mbar, with a gas mix of SiH 4 , H 2 , CO 2 and trimethyl borane (TMB, B(CH 3 ) 3 ) for the doping gas.…”

Thin-film silicon triple-junction solar cell with 12.5% stable efficiency on innovative flat light-scattering substrate

“…The a-Si:H top cell is approximately 270 nm thick and incorporates a recently developed highly transparent p-SiO x doped layer, contributing to high V oc . 27 The front contact is a 2.5-lm-thick boron-doped LP-CVD ZnO layer. As previously explained, EQE measurements were used to determine the J sc .…”