Photovoltaics International Papers

Solar simulators are among the most important and fundamental measurement tools in photovoltaic production facilities as well as in R&D labs. Two major solar simulator technologies can be distinguished: xenon light sources and, more recently, light sources using light-emitting diodes (LEDs). While xenon solar simulators are a well-established technology, LED-based systems appear to be promising candidates for future applications, as they provide a higher flexibility with regard to the flash times, spectral light composition and intensity. Measurement recipes for power quantification under standard test conditions (STC) can be adapted to high-efficiency cells, which require longer flash times. Furthermore, fast inline spectral testing, such as a rapid external quantum efficiency (EQE) test or a rapid reflectivity test, becomes feasible. However, the development of LED-based systems requires well-designed optical and electronic components to ensure high-precision measurements on the basis of a laterally uniform and temporally stable light field.

Today’s industry-standard B-doped monocrystalline silicon still suffers from light-induced degradation (LID) of the carrier lifetime. Illumination at elevated temperatures leads to a so-called regeneration, i.e. a recovery of both the carrier lifetime and the solar cell efficiency. However, even though the carrier lifetime on test wafers increases from about 1ms after processing to 3ms after regeneration, the corresponding PERC+ cell efficiencies in both states are identical; possible reasons for this discrepancy are discussed in this paper.

Silicon heterojunction (SHJ) solar cells are the archetypes of ‘fullsurface passivating contact’ solar cells; such contacts are required in order to achieve typical open-circuit voltages of up to 730–750mV. Although SHJ technology has fewer manufacturing steps and enables higher efficiencies than standard passivated emitter and rear cell (PERC) technology, the market has been slow in taking it up. This paper discusses some of the obstacles that have been overcome in the last 10 years, and shows why the technology is now readier than ever for a competitive mass-market launch.

Stable high voltages in solar cells and modules are becoming increasingly important as large PV systems are being set up in desert regions and are therefore exposed to high temperatures. High-voltage solar cells have lower temperature coefficients and thus produce a higher energy yield for such PV systems. Standard passivated emitter rear cell (PERC) devices have moderate voltages below 680mV, and also have the risk of degrading in such regions, because of light and elevated-temperature induced degradation (LeTID) effects and, in more recent observations, passivation degradation. This paper presents a solution for PERC producers to easily make the switch to n-type passivated emitter, rear totally diffused (nPERT) solar cells, which are capable of stable efficiencies above 22% and voltages close to 700mV, at almost no additional cost.

SolarWorld has played a pioneering role in triggering and implementing the shift from p-type multicrystalline aluminium backsurface field (Al-BSF) to p-type monocrystalline passivated emitter and rear cell (PERC) as the next mainstream solar cell technology, and recognized PERC to be the door opener to an extremely simple and cost-effective implementation of a bifacial solar cell. This paper reviews PERC technology development at SolarWorld, featuring an industrial baseline process for monocrystalline five-busbar (5BB) p-type PERC solar cells exceeding 22.0% median (22.5% maximum) cell efficiency by May 2018, before operations at SolarWorld came to a final halt.

The silicon PV industry has predominantly used silicon wafers sliced by a steel wire, with silicon carbide particles (slurry wire – SW) as an abrasive and polyethylene glycol as a coolant. Low yield, high total thickness variation (TTV), significant material waste and short wire lifetime (and thus high downtime) of SW cutting technology have prompted the wafer slicing industry to develop an alternative technology. Researchers have developed diamond wire (DW) cutting technology for slicing the silicon and demonstrated that it overcomes the drawbacks of SW cutting technology. Although the DW cutting technology has been demonstrated for slicing wafers, the wafer surface is different after the conventional acidic texturing in a silicon solar cell process. It is therefore important to improve the existing process or to develop a new process, in order to produce a homogeneous texturization on DW-cut wafers. In this work, a systematic approach has been pursued to improve the existing process by using an additional etchant (a texture additive) in the acidic mixture. Different etch depths and the corresponding mean reflectance were studied. Optical and morphological studies on DW-cut wafers processed with and without a texture additive have been carried out and interpreted in terms of electrical performance.

The application of electrically conductive adhesives (ECAs) is a promising alternative to the soldering process for cell interconnection in today’s solar module production. ECAs provide an environmentally friendly solution and offer several other advantages over the conventional solder interconnection technology, such as lower processing temperature, higher mechanical flexibility and replacement of toxic lead. When it is proposed to switch from soldering to adhesive technology in a critical process such as the production of solar cell strings, it is necessary to perform a thorough preliminary analysis of the properties of the materials involved, the material compatibilities and the long-term stability of the interconnections within the PV modules.

PV manufacturing capacity expansion announcements in 2018 were significantly impacted by major policy changes mid-year in China. This paper looks in detail at the contrasting developments in the first half of the year, compared with the second half. Attention will also be given to the regional site selection changes as well as to the advanced manufacturing trends emerging in 2018. Finally, after five years of tracking capacity expansion plans, an overview of cumulative expansions, coupled to global solar demand and to capacity trends specifically in China, will be provided.

Ever since the manufacturing of PV modules began suffering from a huge price decline, the reduction of the production cost has been a task of high priority. Digitalization is a subsequent further development of the automation of today’s PV cell and module manufacturing processes and can help to decrease production costs. A central concept of digitalization is the digital twin, which represents the properties and behaviours of physical assets, materials, processes or eventually the entire production line (the so-called smart fab). Different cases of its use are presented in this paper, along with a discussion of the corresponding applications of such digital twins. Finally, a smart fab for PV production is described.

This article reveals the top-10 module suppliers of 2018, based purely on own-brand shipped module MWp-dc volumes. For the past few years, we have sought to compile the top-10 module supplier list before the end of January (or at the latest before the Chinese new year). In practice, with the first two weeks of the year being a reset from any prior-year shipment rush or inventory clear-out, we end up having a couple of weeks to get the top-10 module supplier rankings done.