Rear Emitter Silicon Heterojunction Solar Cells: Fewer Restrictions on the Optoelectrical Properties of Front Side TCOs

We present large-area n-type PERT solar cells featuring a rear boron emitter passivated by a stack of ALD Al 2 O 3 and PECVD SiO x . After illustrating the technological and fundamental advantages of such a device architecture, we show that the Al 2 O 3 /SiO x stack employed to passivate the boron emitter is unaffected by the rear metallization processes and can suppress the Shockley-Read-Hall surface recombination current to values below 2 fA/cm 2 , provided that the Al 2 O 3 thickness is larger than 7 nm. Efficiencies of 21.5% on 156-mm commercial-grade Cz-Si substrates are demonstrated in this study, when the rear Al 2 O 3 /SiO x passivation is applied in combination with a homogeneous front-surface field (FSF). The passivation stack developed herein can sustain cell efficiencies in excess of 22% and V o c above 685 mV when a selective FSF is implemented, despite the absence of passivated contacts. Finally, we demonstrate that such cells do not suffer from light-induced degradation.

Section: Front Versus Rear Emitter Configurationmentioning

confidence: 88%

Large-Area n-Type PERT Solar Cells Featuring Rear p⁺ Emitter Passivated by ALD Al₂O₃

Cornagliotti

Urueña

Aleman

et al. 2015

“…The detailed reasons for these high values are yet to be clarified; yet, possible explanations include high crystallinity, resulting in high doping efficiencies and hence improved contact and series resistance [52]. An additional possibility to be taken into account is the rear-side hole collection [70]. Comparing these results with the all-amorphous reference device fabricated in the same run clearly shows both the optical but also electrical benefits of μc-Si:H. However, to be fair, the reference we show here exhibits slightly lower performance (best cell: 716.7 mV, 36.7 mA/cm 2 , 77.3%, and 20.4%); yet, the lower V oc cannot account for a difference of >2% absolute in FF with respect to the best μc-Si:H device.…”

Section: (C) and (D)]mentioning

confidence: 99%

Strategies for Doped Nanocrystalline Silicon Integration in Silicon Heterojunction Solar Cells

Seif

Descoeudres

Nogay

et al. 2016

Carrier collection in silicon heterojunction (SHJ) solar cells is usually achieved by doped amorphous silicon layers of a few nanometers, deposited at opposite sides of the crystalline silicon wafer. These layers are often defect-rich, resulting in modest doping efficiencies, parasitic optical absorption when applied at the front of solar cells, and high contact resistivities with the adjacent transparent electrodes. Their substitution by equally thin doped nanocrystalline silicon layers has often been argued to resolve these drawbacks. However, low-temperature deposition of highly crystalline doped layers of such thickness on amorphous surfaces demands sophisticated deposition engineering. In this paper, we review and discuss different strategies to facilitate the nucleation of nanocrystalline silicon layers and assess their compatibility with SHJ solar cell fabrication. We also implement the obtained layers into devices, yielding solar cells with fill factor values of over 79% and efficiencies of over 21.1%, clearly underlining the promise this material holds for SHJ solar cell applications.Index Terms-Microcrystalline silicon, nanocrystalline silicon, silicon heterojunctions (SHJs), solar cells.

“…This design increased the short current density, Jsc, due to the more transparent and lower parasitic absorption nanocrystalline silicon n layer (nc-Si:H) used as a front surface field (FSF) compared to the amorphous silicon based (p) layer of the emitter. Moreover, this configuration allows for using less conductive TCOs due to the additional contribution of the ntype silicon wafer to lateral carrier transport [3]. Introducing optimized wet chemistry processes for random pyramid texturing, allowed a further improvement in Jsc due to an optimized and more homogeneous pyramid size.…”

Section: Introductionmentioning

confidence: 99%

ITO-Free Silicon Heterojunction Solar Cells With ZnO:Al/SiO₂ Front Electrodes Reaching a Conversion Efficiency of 23%

Morales-Vilches

Cruz

Pingel

et al. 2019

Silicon heterojunction solar cells (SHJ) have been increasingly attracting attention to the PV community in the last years due to their high efficiency potential and the lean production process. We report on the development of a stable baseline process for SHJ cells with a focus on the optical improvement of the solar cells' front side. An amorphous silicon oxide layer (a-SiO 2 ) was used as an anti-reflective coating (AR) on top of the finished SHJ devices. Both optical simulations and experimental results demonstrate a short circuit current density (J sc ) improvement of 0.4 mA/cm 2 when applying the a-SiO 2 AR, yielding maximum conversion efficiencies of 23.0 %. Full-size cells with 244-cm 2 total area have been produced using three front contact stacks: ITO as reference, ZnO:Al and ZnO:Al/SiO 2 showing the J sc improvement with the double AR configuration. Damp-heat tests on those samples are currently being carried out.