High-efficiency Silicon Heterojunction Solar Cells: A Review

Abstract

Abstract. Silicon heterojunction solar cells consist of thin amorphous silicon layers deposited on crystalline silicon wafers. This design enables energy conversion efficiencies above 20% at the industrial production level. The key feature of this technology is that the metal contacts, which are highly recombination active in traditional, diffused-junction cells, are electronically separated from the absorber by insertion of a wider bandgap layer. This enables the record open-circuit voltages typically associated with heterojunction devices without the need for expensive patterning techniques. This article reviews the salient points of this technology. First, we briefly elucidate device characteristics. This is followed by a discussion of each processing step, device operation, and device stability and industrial upscaling, including the fabrication of solar cells with energyconversion efficiencies over 21%. Finally, future trends are pointed out.

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

“…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.…”

Applicability of photonic sintering and autoclaving as alternative contact formation methods for silicon solar cells with passivating contacts

“…In the BSC cell design, stacks of intrinsic and doped hydrogenated amorphous silicon (a-Si) layers on both sides of textured ntype silicon wafers are used to form carrier-selective heterojunctions that exhibit excellent passivation properties [5,6]. Transparent conductive oxide (TCO) layers on top of both sides of the cells enable an electrical contact between the a-Si layers and the metal electrodes.…”

“…Transparent conductive oxide (TCO) layers on top of both sides of the cells enable an electrical contact between the a-Si layers and the metal electrodes. To avoid degradation of the passivation quality, back-end processing of SHJ solar cells needs to be performed at temperatures in the range of 200°C, which is low compared to firing of standard diffused junction solar cells at 800-900°C [5,6]. Therefore, non-firing-through polymer-based silver pastes for screen printing are to be used.…”

“…These pastes are thermally activated in the range of 200°C and are recommended by paste manufacturers to be cured for 15-30 min. Then, the screen-printed contact fingers exhibit lateral resistivities (specific resistances lengthways the fingers)  l of above 6 µcm [5][6][7]. This is correlated with significant ohmic losses and a reduced efficiency on cell level.…”

Investigation of silicon heterojunction solar cells by photoluminescence under DC-bias

“…Moreover, given that the a-Si:H thin layers are deposited at low temperature, namely 200 • C, by plasma processes, the thermal budget of this technology is low. Although HJ solar cells have been commercialised for fifteen years and a record cell efficiency of 24.7% has been reported 1 , there is still an issue regarding the properties of the c-Si/a-Si:H interfaces, which condition the solar cell performances [1]. More precisely, since the cells are processed on high quality monocrystalline silicon wafers, the a e-mail: guillaume.courtois@polytechnique.edu 1 Panasonic, Press release, Feb. 12th, 2013 efficiency of the interface defect passivation is of crucial importance.…”