Technical Papers

Germany and Italy are forecasted to drive solar demand to new highs in 2011, with rumours of installations up to 22GW on the cards for this year. The German and Italian markets, scheduled to peak in 2011 and 2012, respectively, face a potential problem in terms of where to sell their modules if these two countries cannot accommodate 10GW of installations per year. The emerging markets can solve part of this challenge and will deliver new opportunities to the solar industry. Some Asian, European and Middle Eastern regions will require up to of 6GW of solar-generated electricity, while the Americas, Africa and Australia are each projected to install approximately 1GW in 2014. This paper takes a look at the development of these emerging markets and provides a projection of likely installation figures up to 2015.

Laser-doped selective emitter (LDSE) technology, invented and patented by the University of New South Wales (UNSW), is presently generating considerable interest in the photovoltaics industry due to its low cost, high efficiency, and suitability for mass production. The excellent results achieved to date – as high as 19.7% on small area laboratory test devices [1], and 19.0% on industrial large-area 156mm wafers [2] – are attracting a similarly impressive array of commercial partners. Nearly 10 companies are at various stages of implementation of LDSE technology variants into production and pilot production. This paper takes a closer look at the potential for mass production of LDSE-based solar cells.

As recently as a couple of years ago, solar panels based on thin-film manufacturing technology were being promoted as the low-cost alternative to crystalline silicon. Not only was it cheaper, but thin film also had a convincing roadmap which guaranteed this cost advantage for the foreseeable future. That was 2008, when persistently high polysilicon prices seemed inevitable as demand for solar electricity boomed. We now know that assumption to be false, and although we all knew polysilicon prices would fall eventually, no one predicted the speed and magnitude with which they crashed: in the space of several months, prices reached the point where any advantage associated with the lower materials costs of thin-film manufacturing were completely blown away.

This article highlights an alternative method for increasing short-wavelength external quantum efficiency (EQE) and hence overall conversion efficiency of mc-Si PV modules via luminescent down-shifting (LDS), a technique originally proposed by Hovel et al. [1] in 1979. The potential for efficiency enhancement via LDS has been either predicted or measured for a wide range of PV technologies (see [2] for a review). However, in this article, we will highlight how LDS can be incorporated into the existing encapsulation layer, avoiding any modification to well-established solar cell manufacturing processes and thus offering the potential of a production-ready technology.

Conversion efficiencies of thin-film silicon solar cells can be increased by nanotexturing of the cells. This nanotexturing step allows for a larger fraction of the incoming light to scatter and diffract, so that both the total absorption of light in the solar cell and the short circuit current is enhanced. In this study, we investigate the optics of thin-film silicon solar cells by numerically simulating Maxwell’s equations by a finite-difference time-domain algorithm. Starting with periodically textured solar cells, the influence of the texture period and height on the quantum efficiency and short circuit current were investigated. With this understanding of the optimized surface texture for periodically textured solar cells, the possibility of interpreting the optics of randomly textured solar cells will be discussed.

The majority of solar module manufacturers use ethylene-vinyl acetate (EVA) copolymer foils as the encapsulant material for solar cells and thin-film modules. Because EVA needs long processing times for curing, thermoplastic process materials that do not employ chemical cross-linking have been coming more and more into focus in the encapsulation sector. This paper takes a look at the mechanical temperature-dependent properties of a variety of such materials.

Ammonia, a gas which has its roots in livestock farming, can have potentially detrimental effects on the lifetime and reliability of PV modules. Research into the degree of corrosive effects of this gas on modules is of utmost importance for any module manufacturer guaranteeing a certain specific lifetime for their product. Researchers from SCHOTT and SCHOTT Solar together with the DLG (Deutsche Landwirtschafts-Gesellschaft/German agricultural society) developed a test design involving humidity, temperature and ammonia gas. This design is based on permeation testing and microscopic analysis of samples aged under a controlled atmosphere or from outdoor exposure. Additionally, a highly accelerated test is presented which allows screening materials for use in PV modules within 84 hours. An Arrhenius type of model is used to calculate the acceleration factors involved. Based on this model, the proposed test design is equivalent to more than 20 years of outdoor exposure in the rural environment (in Central Europe).

The aim of this work is to study the effects of dark lines on the face of polycrystalline silicon solar cells. The formative processes of dark lines were observed by laser scanning microscopy. Following the initial appearance of a few etch pits on the surface of the cells, extending the etching time saw these etch pits increase in size, eventually merging to form a single line, known as a ‘dark line’. Dark lines are lines that are linked together by a series of contiguous dislocation outcrops and have the potential to reduce silicon wafer lifetime, adversely affect both the electroluminescence and the quantum efficiency of a solar cell, and have resulting negative effects on the cell’s electrical properties.

Savvy solar panel manufacturers understand that wringing excess costs from every stage of the value chain is simply the price of admission to today’s crowded market. They also know that reliability and quality are not only critical for delivering on a 25-year warranty promise, but also drive the true cost of energy over the lifetime of the system. This factor is becoming increasingly apparent, especially in industrial- and utility-scale solar projects, as they age and the power output of many lower quality systems begins to degrade to unexpected levels. Many of those systems used UL or IEC certifications as a proxy for good reliability. Unfortunately, UL certification is primarily concerned with user safety, and even the IEC requirements are not rigorous enough to ensure trouble-free operation throughout the system lifetime. High reliability and quality require testing and manufacturing methods that go far beyond the certification tests.

This paper focuses on the latest developments from research on MWT (metal wrap-through) solar cells at Fraunhofer ISE. An overview of the current cell results for mc-Si and Cz-Si material with both Al-BSF and passivated rear side is presented. Recent progress in cell technology and challenges to reaching efficiencies of 20% for industrially processed large-area MWT solar cells are also discussed. Up to recently, MWT cell efficiencies of up to 19% for Cz-Si and up to 17.5% for mc-Si have been reached with industrially feasible processing. Improvements to the design of the MWT cell to increase cell efficiency and to allow an easy module assembly are also presented in this paper, as are first calibrated IV measurements of MWT solar cells.