Photovoltaics International Papers

This paper reports on the latest advances in passivated emitter and rear cell (PERC)-based shingled solar cell activities at Fraunhofer ISE. The approach taken is to fabricate 6" host wafers from Czochralski-grown silicon and separate them after metallization and contact firing into bifacial p-type shingled passivated edge, emitter and rear (pSPEER) solar cells.

Heterojunction technology is currently a hot topic actively discussed in the silicon PV community. Hevel recently became one of the first companies to adopt its old micromorph module line for manufacturing high-efficiency silicon heterojunction (SHJ) solar cells and modules. On the basis of Hevel’s own experience, this paper looks at all the production steps involved, from wafer texturing through to final module assembly.

This paper presents the calibration of solar cells, in accordance with the IEC 60904 standards, carried out at the solar cell calibration laboratory of the Calibration and Test Center (CalTeC) at the Institute of Solar Energy Research Hamelin (ISFH). For the calibration of a solar cell, the cell area, the spectral responsivity (SR) and the current–voltage (I–V) curve have to be determined. The I–V curve then yields the characteristic parameters, including the power conversion efficiency, fill factor, short-circuit current and opencircuit voltage. The required measurement facilities and contacting stages are explained in detail; in addition, the measurement procedures are introduced. The precision and accuracy of the resulting characteristic parameters and curves are demonstrated by recent intercomparisons between different international calibration laboratories.

Passivated emitter and rear cell (PERC) solar cell design is the industry standard for high-volume solar cell manufacturing today. The next challenge for the PV industry is to find a low-cost cell upgrade technology platform that can be easily retrofitted in existing production lines to modify the front side and enhance the rear. The monoPolyTM technology platform, developed at SERIS together with its strategic industry partners, offers an attractive solution and paves the way for the adoption of passivating contacts in large-scale manufacturing. This platform requires only one tool upgrade for most PERC/T production lines, has one less process step than a standard PERC production process, and yields a +1%abs. efficiency boost over a standard PERC process. The authors believe that monoPoly will enable the PV industry to mass produce cells with efficiencies exceeding 24% in their existing lines in the near future.

The PV industry is undergoing rapid technology changes that have been driven by the well-documented swift adoption of monocrystalline wafers. Less well understood, however, is that within this wafer technology transition comes a shift to larger wafer sizes, and this includes p-type and n-type mono-Si wafers.

This paper explains how these modern production concepts are implemented in ISC’s lab, and details the plans for their utilization in future production sites, with illustrations of the key benefits in practice. With these modern manufacturing concepts, it will even be possible to bring future c-Si PV production back to the EU with the choice of an appropriate cell concept (high efficiency but proven technology, e.g. interdigitated back-contact (IBC) cells, such as ZEBRA) and a sound business plan.

Today, solar power is one of the cheapest ways of providing energy internationally, partly because of the excellent R&D work in Europe. Prices of modules have fallen by half in the past three years, and at the same time the use of solar power has been steadily increasing. The reason why there has been an increase in the use of solar energy in Europe and Germany is the achievement of the climate targets of the Paris Agreement. While the machines for the production of solar modules are still manufactured in Germany, the production of cells has now almost completely migrated to Asia. Therefore, the VDMA commissioned a study from Fraunhofer ISE to evaluate whether the production of solar modules at competitive costs could again be realized in Europe. This paper presents the results of the VDMA study.

Solar modules with half-size solar cells have the potential for becoming the new standard. The cutting of cells leads to electrical recombination losses at the cell level, which are more than compensated by reduced resistive losses as well as by current gains at the module level. At the same time, the cutting process must be optimized to avoid mechanical damage that could lead to cell breakage in the module. Module design opportunities for hot-spot protection, shading resistance and energy yield optimization are presented in this paper. Module power can be increased by 5–8%, which justifies the investment in additional equipment for cell cutting, stringing, lay-up and bussing. Half-cell technology is highly attractive for new solar module production capacity.

Bifacial cells and modules collect light falling not only on the front side of the panels but also on the rear; this additional collection of light increases the total absorbed irradiance, and accordingly the generated current. One of the remaining questions is: what temperature do bifacial solar panels operate at compared with monofacial panels? The extra light absorption at the rear will heat up the modules more, but at the same time, the parasitic heating by the absorption of infrared light is reduced, because infrared light is mostly transmitted through the glass–glass panels. In this paper, different bifacial and monofacial cell and module architectures are considered for the calculation of the energy spectra for all heat loss and absorption processes and the effective heat input. The heat transfer coefficients and the heat capacities of modules with different rear panels are given. Actual module temperatures for different layouts are presented and discussed for low- and high-irradiance (diffuse/direct) conditions in the Netherlands.

Tandem solar cells combine several solar cells with different photoabsorbers, stacked in a descending order of bandgap energies. They come in many flavours, but one promising combination is a bottom cell of c-Si or copper indium gallium selenide (CIGS) and a top cell of perovskite. Perovskite solar cells are thin-film solar cells with many advantages, such as a low-cost, high-throughput sheet-to-sheet and rollto- roll production, and a tuneable bandgap. Their long-term instability, however, is a challenge that needs to be overcome in order to make these cells a success. In this paper it is demonstrated that, by combining comprehensive loss-reduction strategies with effective large-area fabrication, perovskite-based tandem solar modules have the potential to yield power conversion efficiencies (PCEs) that are significantly higher (PCE of up to 45%) than those of established PV technologies, and can be manufactured on an industrial scale.