Development of New a-Si/c-Si Heterojunction Solar Cells: ACJ-HIT (Artificially Constructed Junction-Heterojunction with Intrinsic Thin-Layer)

Carrier recombination at the metal contacts is a major obstacle in the development of high-performance crystalline silicon homojunction solar cells. To address this issue, we insert thin intrinsic hydrogenated amorphous silicon [a-Si:H(i)] passivating films between the dopant-diffused silicon surface and aluminum contacts. We find that with increasing a-Si:H(i) interlayer thickness (from 0 to 16 nm) the recombination loss at metal-contacted phosphorus (n+) and boron (p+) diffused surfaces decreases by factors of ∼25 and ∼10, respectively. Conversely, the contact resistivity increases in both cases before saturating to still acceptable values of ∼ 50 mΩ cm2 for n+ and ∼100 mΩ cm2 for p+ surfaces. Carrier transport towards the contacts likely occurs by a combination of carrier tunneling and aluminum spiking through the a-Si:H(i) layer, as supported by scanning transmission electron microscopy–energy dispersive x-ray maps. We explain the superior contact selectivity obtained on n+ surfaces by more favorable band offsets and capture cross section ratios of recombination centers at the c-Si/a-Si:H(i) interface.

Section: A Interface Passivationmentioning

confidence: 95%

Amorphous silicon passivated contacts for diffused junction silicon solar cells

Bullock

Yan

Wan

et al. 2014

“…With stacks of intrinsic and doped a-Si:H layers, excellent surface passivation can be achieved, leading to high open-circuit voltages in excess of 720 mV. 1,2 The drawback of the amorphous emitter is its low mobility, which, together with a thickness limited to a few nanometers to reduce light absorption losses, 3,4 results in a high resistivity. To overcome this disadvantage and achieve high efficiencies, a transparent conductive oxide (TCO) layer is required on top of the emitter for lateral transport of photogenerated charge carriers to metal finger contacts; the TCO also serves as a single-layer antireflection coating.…”

Section: Introductionmentioning

confidence: 99%

Analysis of lateral transport through the inversion layer in amorphous silicon/crystalline silicon heterojunction solar cells

Filipič

Holman

Smole

et al. 2013

In amorphous/crystalline silicon heterojunction solar cells, an inversion layer is present at the front interface. By combining numerical simulations and experiments, we examine the contribution of the inversion layer to lateral transport and assess whether this layer can be exploited to replace the front transparent conductive oxide (TCO) in devices. For this, heterojunction solar cells of different areas (2 Â 2, 4 Â 4, and 6 Â 6 mm 2 ) with and without TCO layers on the front side were prepared. Laser-beam-induced current measurements are compared with simulation results from the ASPIN2 semiconductor simulator. Current collection is constant across millimeter distances for cells with TCO; however, carriers traveling more than a few hundred microns in cells without TCO recombine before they can be collected. Simulations show that increasing the valence band offset increases the concentration of holes under the surface of n-type crystalline silicon, which increases the conductivity of the inversion layer. Unfortunately, this also impedes transport across the barrier to the emitter. We conclude that the lateral conductivity of the inversion layer may not suffice to fully replace the front TCO in heterojunction devices. V C 2013 AIP Publishing LLC.

“…[5][6][7] For this reason, typically, a few nanometer thin intrinsic buffer layer is inserted between the c-Si surface and the doped a-Si: H films for device fabrication. 8 For HJ solar cells featuring such stacked film structures, impressive large area ͑Ͼ100 cm 2 ͒ energy conversion efficiencies ͑Ͼ22%͒ have been reported. 9,10 Despite this result, the fundamental origin of the poor passivation of the doped a-Si: H / c-Si interface is not yet fully understood.…”

Section: Introductionmentioning

confidence: 99%

Nature of doped a-Si:H/c-Si interface recombination

Wolf¹,

Kondo²

2009

207

132

Doped hydrogenated amorphous silicon ͑a-Si: H͒ films of only a few nanometer thin find application in a-Si: H/crystalline silicon heterojunction solar cells. Although such films may yield a field effect at the interface, their electronic passivation properties are often found to be inferior, compared to those of their intrinsic counterparts. In this article, based on H 2 effusion experiments, the authors argue that this phenomenon is caused by Fermi energy dependent Si-H bond rupture in the a-Si: H films, for either type of doping. This results in the creation of Si dangling bonds, counteracting intentional doping of the a-Si: H matrix, and lowering the passivation quality.