Photovoltaics International Papers

There are numerous tools and methods available on the market for the optical and electrical quality control of high-efficiency silicon solar cells during their industrial production, and even more are discussed in the literature. This paper presents a critical review of the possibilities and limitations of these tools along the value chain, from wafer to cell, in the case of passivated emitter and rear cells, as well as a discussion of some showcases. Economic and technological challenges and future trends are addressed.

High-performance multicrystalline (HPM) silicon, achieved by nucleation on special seed layers at the crucible bottom, is now increasingly replacing conventional multicrystalline (mc) silicon, which is solidified on the standard silicon nitride coating. The HPM material is characterized by a very fine initial grain structure consisting of small, regularly shaped grains surrounded by a large number of random-angle grain boundaries. These grain structure properties, which differ significantly from those of conventional multicrystalline silicon, lead to a much lower dislocation content in the material, and therefore result in higher efficiencies of the silicon solar cells produced. This paper gives a rough overview of the worldwide R&D activities on HPM silicon in recent years, supplemented by several research results obtained at Fraunhofer IISB/THM. The focus is on the different seeding methods, the grain structure properties and the development of the grain and defect structure over the ingot height, as well as on the main challenges for further improvements in material quality and production costs.

Having installed more than 75 gigawatts in 2016, the solar industry continues to create opportunities for cell and module manufacturers to expand capacities, while upgrading technologies and improving process flows. Supply remains dominated by p-type crystalline silicon modules, despite ongoing research into n-type variants and the addition of PERC on p-type mono cells. The efficiency increases from p-type mono are now driving p-type multi cell producers to accelerate changes to production lines from both black silicon and PERC. This is now setting new benchmarks for the supply of solar modules in 2017 to utility-scale solar installations.

A novel nanoscale pseudo-pit texture has been formed on the surface of a multicrystalline silicon (mc-Si) wafer by using a metal-catalysed chemical etching (MCCE) technique and an additional chemical treatment. A desirable nanoscale inverted-pyramid texture was created by optimizing the recipe of the MCCE solution and using a proprietary in-house chemical post-treatment; the depth and width of the inverted pyramid was adjustable within a 100–900nm range. MCCE black mc-Si solar cells with an average efficiency of 18.90% have been fabricated on CSI’s industrial production line, equating to an efficiency gain of ~0.4%abs. at the cell level. A maximum cell efficiency of 19.31% was achieved.

This paper presents an in-depth analysis of state-of-the-art p-type monocrystalline Czochralski-grown silicon passivated emitter and rear cells (PERCs) fabricated in a near-industrial manner. PERC solar cells feature a homogeneous emitter on the front side, and an Al2O3 passivation layer and local contacts on the rear side.

Even though it is now more than five years since potential-induced degradation (PID) began to proliferate, and despite the fact that solutions are under development, it is currently still the most discussed mode of degradation associated with cracking in PV modules.

Conventional ribbons used for interconnecting solar cells in PV modules act like mirrors, causing a large proportion of incident light to be lost. Experimental results indicate that only around 5% of the perpendicular incident light on the connections can be reused; as a result, this area contributes very little, if at all, to the current generation.

A highly promising concept for future solar cells is the heterojunction (HJT) architecture; according to the ITRPV roadmap 2016, the market share for HJT solar cells will increase to 10% by 2026. Over this timescale, stabilized cell efficiency will increase to 24%, which is the second-highest predicted efficiency after backcontact cells with n-type mono-Si. Moreover, metallization of HJT cells offers the advantage of using low-temperature steps, which reduces energy consumption and hence production costs.

This paper presents the fabrication of front-junction n-type silicon solar cells with Cu-plated electrodes, using laser contact opening and forward-bias plating. The cells feature a back-surface field formed by a phosphorus implant, and a diffused boron emitter with aluminium oxide passivation. Laser ablation of the front-side dielectric layers is followed by a metallization based on Ni/Cu forward-bias plating, while sintered metal paste is used for the rear electrode. The results show improved line conductivity and contact resistivity for the plated electrode, leading to higher solar cell efficiency than for cells made with conventional Ag/Al paste. On 6" n-type Czochralski wafers, cell efficiencies of up to 21.3% have been demonstrated, with an open-circuit voltage of 654mV, a short-circuit current of 40.8mA/cm2 and a fill factor of 79.8%.

Perovskite microcrystals have properties that make them uniquely suitable as a basis of thin, light, semitransparent solar modules. However, there are some remaining challenges, including lifelong stability, that need to be tackled before this technology can become commercially available.