A recent revitalization of the passivated emitter and rear cell (PERC) concept in the silicon PV industry has resulted in solar energy conversion efficiencies of greater than 20% being achieved on p-type solargrade single-crystalline silicon (mono-Si) wafers during the past two years or so, thanks to technological advance in the use of aluminium oxide for silicon surface passivation. The research efforts carried out at JA Solar in developing an industry version of PERC cells that can be mass produced utilizing the existing conventional back-surface field (BSF) cell manufacturing platform with moderate retrofitting have yielded 20.5% average conversion efficiency, which can be consistently achieved on p-type Si wafers grown by the Czochralski method. Moreover, the experimental results showed that an average conversion efficiency of 20% is achievable when, in combination with JA Solar’s proprietary light-trapping technique, the same technological approach is applied to the cells using high-quality polycrystalline silicon (multi-Si) wafers produced by the seeded directional solidification method.
In this paper large-area (239cm2) n-type passivated emitter, rear totally diffused (n-PERT) solar cells are compared with state-of-the-art p-type passivated emitter and rear cells (p-PERC) to evaluate potential advantages of n-PERT over p-PERC. In particular, an investigation has been carried out of fully screenprinted bifacial n-PERT solar cells, in which the boron-doped emitter is contacted with aluminiumcontaining silver (AgAl) pastes, as well as of n-PERT back-junction (BJ) solar cells, in which the B-doped emitter is locally contacted with screen-printed Al. Using two separate quartz furnace diffusions for the B- and P-doped regions, efficiencies of up to 20.3% on bifacial n-PERT solar cells and of up to 20.5% on n-PERT BJ solar cells were achieved. In comparison, reference p-PERC solar cells that were processed in parallel achieved efficiencies of up to 20.6% before light-induced degradation (LID), but degraded to 20.1% after 48 hours of illumination. In addition, ion implantation and pre-deposition of dopant sources have been evaluated as alternative technologies for forming the full-area doping of the front and rear wafer surfaces, thus reducing the number of processing steps for n-PERT solar cells. Using ion implantation and a co-annealing step, efficiencies of up to 20.6% for bifacial n-PERT solar cells have been achieved, and of up to 20.5% for n-PERT solar cells, in which the P-doped back-surface field is contacted with evaporated Al. By employing a boron silicate glass (BSG) deposited via plasma-enhanced chemical vapour deposition (PECVD) as a dopant source, along with a co-diffusion step, n-PERT BJ solar cells have been fabricated with up to 19.8% energy conversion efficiency.
The aim of this paper is to dispel the common belief that bifaciality is nonsense as it is not a mature technology, it is expensive and, because in large systems there is limited albedo from the rear side, it only serves the niche market. A complete picture of bifacial cell technologies and module concepts is presented, as well as levelized cost of electricity (LCOE) results for present and future bifacial systems.
One question to emerge in recent years is whether monocrystalline silicon (mono-Si) or multicrystalline silicon (mc-Si) will become the dominant mainstream technology in the future PV industry. However, despite all the arguments, the market share of mc-Si seems barely changed, while the market share of mono-Si has not increased significantly. The reasons why mono-Si has not made progress have been extensively mentioned in the literature and will therefore not be covered here; rather, the objective of this paper is to discuss several benefits of mono-Si.
Global PV end-market demand for PV modules is expected to reach around 50GW in 2014, which has prompted the need for manufacturers to expand capacity to meet demand. With effective module capacity standing at around 45GW at the end of 2013, Photovoltaics International (PVI) has analysed solar cell, c-Si and thin-film capacity expansion announcements that were extensively reported by sister website, PV Tech, from the beginning of 2014 through to the end of November to establish key trends.
Looking back, 2014 was a year of convalescence for a PV industry still battered and bruised from a period of ferocious competition. End-market demand continued apace, with analysts towards the end of 2014 predicting the year would see between around 45 and 50GW of deployment. That has begun to feed through to the supplier end of the market, with all the main manufacturers announcing capacity expansions in 2015 and further ahead.
A detailed analysis of state-of-the-art CIGS technology has resulted in a direct cost of ownership (CoO) of €0.44/Wp for this PV module type. However, the reduction in production costs, although impressive, is not sufficient for CIGS to become competitive with today’s c-Si technology. In order to answer the question as to whether CIGS will ever be able to challenge c-Si, the cost-reduction potential of CIGS is investigated. The impact of savings is evaluated in respect of the material segment, production equipment, energy and labour, production yield, device efficiency and absorber thickness. A total cost-reduction potential of around €0.21/ Wp is identified, which would be enough to put CIGS back into the game (the direct CoO will continue to be dominated by material and equipment depreciation, adding up to 68%). These cost reductions, however, cannot be realized immediately: within the next two years, €0.03/Wp is expected to be feasible, while it will take two to four years for the next €0.107/Wp. For the final €0.073/Wp, a time frame of at least five years is predicted, with corresponding costs for the technology developments. Provided that someone is willing to spend the necessary amount of time and money, the second part of the answer regarding CIGS’ competitiveness will depend on how c-Si evolves within this time period.
This paper reports on the progress of R&D in two n-type cell and module concepts: the n-Pasha solar cell and bifacial module, and the n-MWT (metal wrap-through) cell and module. Both are part of ECN's technology platform, acting as a roadmap for research in n-type Cz cells and modules. The technology platform also encompasses low-cost IBC solar cells. In the case of n-Pasha, recent developments involve improved stencilprinted metallization, resulting in an increased Isc and Voc and efficiencies of up to 20.5%. For the bifacial module aspect, research has been done on the effect of different albedo on the module output. A gain of 20%rel in module output power was obtained with an optimized background, increasing the module power from 314W to 376W. As regards n-MWT cells, the front-side metallization pattern has been changed significantly. The number of vias for conducting the emitter current to the rear has been increased from 16 to 36, resulting in reduced lengths of busbars and fingers and consequently an increase in FF. At the same time, the metal coverage on the front side has been reduced from 5% to 3% of the total area, leading to a gain in Isc and Voc and a significant reduction in Ag consumption. All these factors will result in a lower cost/Wp. For the improved n-MWT design, average efficiencies of 20.8% over a large batch (134) of cells have been obtained, with the highest recorded efficiencies being 21.0%.
This paper presents the first 60-cell module results from a very simple process scheme for creating fully plated nickel-copper contacts on crystalline silicon solar cells. Standard Cz back-surface field (BSF) cells are processed in a completely analogous way to the standard process sequence up to and including rear-side screen printing. After a firing step for BSF formation, the front-grid positions are defined by picosecond pulse laser ablation and plated with nickel, copper and silver; this is followed by a short thermal anneal. Cell classification produces a very neat efficiency distribution of 19.6±0.1%. Solder and peel testing shows this approach to be competitive with standard screen-printed contacts in terms of adhesion. A batch of 60-cell modules were fabricated from the cells in a standard automated tabber-stringer system and subjected to thermal cycling and damp heat testing as part of the IEC 61215 reliability test sequence. The modules passed the test sequence without showing any signs of electrical degradation caused by, for example, copper diffusion.
The PV industry is intensively evaluating technologies for further increasing conversion efficiency while maintaining, or even further reducing, production costs. Two promising technologies that meet these objectives are 1) the passivated emitter and rear cell (PERC), which reduces optical and recombination losses of the solar cell's rear side; and 2) multi-busbar/multi-wire module interconnection, which reduces optical and resistive losses of the front grid. This paper evaluates a combination of these two technologies, in particular industrial PERC solar cells with printed metal contacts employing a five-busbar (5BB) front grid instead of the typical three-busbar (3BB) design. The resulting 5BB PERC solar cells demonstrate an independently confirmed conversion efficiency of 21.2%, compared with the 20.6% efficiency for 3BB PERC cells. To the authors' knowledge, a value of 21.2% is the highest reported so far for typical industrial silicon solar cells with printed metal front and rear contacts. The higher conversion efficiency is primarily due to an increased short-circuit current, resulting from the reduced shadowing loss of the 5BB front-grid design, in combination with stencil-printed finger widths of only 46μm.
