Area 2 Abstract

Area 2: Crystalline silicon materials and solar cells

Trina Solar, China

Will we have >22%  Efficient Multi-Crystalline Silicon Solar Cells?

Multicrystalline Silicon technologies represents more than 65% of 2015 global shipments. Over the last two years, the best p-type multicrystalline silicon solar cells developed by Trina Solar have reached new efficiency records, up to 20.86% in 2014 and 21.25% in 2015. These achievements result from improvements of all aspects of the solar cell fabrication: contamination control, development of high-performance multi-crystalline silicon wafers, cell design and process optimization. Analysis show that efficiencies above 22% are possible with p-type multi-crystalline and could be reached in the next few years.

University of New South Wales, Australia

Ultra-thin Silicon Solar Cell for Lightweight Steel Roofs 

The majority of commercial roofs in Australia and 40% of those USA are made of thin steel sheeting that is not structurally capable of supporting the weight of conventional glass-based PV modules. We are developing a building-integrated photovoltaic (BIPV) roofing material to be factory integrated with low cost steel roofs for commercial buildings. This roofing product is based on the Ultra-Thin Silicon on steel (UTSi) solar cell, fabricated via epitaxial growth of a thin layer of monocrystalline silicon grown on porous silicon. This work has been done in collaboration with AmberWave, Inc. Verified efficiencies of up to 16.8% on 4 cm2 devices and 15.9% on 90 cm2 devices have been demonstrated to date, both with an active layer thickness of just 18 µm. The near term solar cell efficiency potential of the UTSi solar cell is well above 20%.  Details of the solar cell and its value when applied to a steel roof component will be described. 

Max Planck Institute of Microstructure Physics, Halle, Germany

Local Efficiency Analysis of c-Si Solar Cells Based on Luminescence Imaging and Lock-in Thermography

Photoluminescence and electroluminescence imaging and dark lock-in thermography (DLIT) are used for imaging the local series resistance Rs and saturation current density J01, which are essential parameters for local efficiency analysis. The limitation of DLIT is thermal blurring and a higher data acquisition time. However, J01 results for luminescence and DLIT analysis did not agree quantitatively. The reason is the assumption of the model of independent diodes for evaluating the data, whereas in reality Rs is a distributed resistance. This assumption leads to significant errors only for evaluating luminescence images, but not for evaluating DLIT, where the current is measured more directly. Recently two alternative PL evaluation methods were proposed, which are not based on the isolated diode model and lead to high-resolution J01 images comparable to DLIT ones. Together with EL and PL based local voltage analysis this enables a realistic Griddler analysis of inhomogeneous solar cells.

Hanwha Q Cells GmbH, Germany

The 7th edition of the International Technology Roadmap for Photovoltaic (ITRPV) – current trends and future challenges in c-Si PV

The photovoltaic (PV) industry has to provide power generation products that are competitive to conventional and other renewable sources of energy. The sales price of PV modules has been experiencing a continuous learning since 60 years. End of 2015 the prices reached an acceptable level of about 0.6$/Wp at a cumulative PV module shipment of 234GWp. But production capacity grows above market demand. So we experience today new round of oversupply and falling prices – below 0.4 $ /Wp currently.

Identifying technological trends and defining requirements for necessary improvements is mandatory in order to be successful in this dynamic and competitive environment.

The ITRPV identifies c-Si PV key process and product parameters and discusses trends and challenges being essential for a continuation of the PV price learning curve.

The presentation discusses important findings of the ITRPV’s 7th edition. Some technical trends for the improvement of cell and module efficiency will be discussed regarding future cost reduction potentials. LCOE (Levelised Cost Of Electricity) consideration emphasizes the long-term competitiveness of PV based power generation.

A discussion of possible growth scenarios will analyze the current situation of the PV industry in comparison to historic industrial developments and a biological process

Jinko Solar, China

>21% high efficiency industrial screen-printed multicrystalline silicon solar cell

In this paper, we demonstrate industrially feasible large-area solar cells achieving record energy conversion efficiencies of >21% on p-type boron doped multicrystalline silicon wafers. Advanced light trapping and passivation technologies are used to achieve excellent light absorption and very low surface recombination velocity. The bulk lifetime of the multicrystalline silicon wafers used for the fabrication exceeds 600µs after optimized gettering and hydrogenation processes. The high bulk lifetime and excellent surface passivation enable the open circuit voltage of the cells to exceed 665mV. The metallization process is done by screen printing utilizing optimized front and back patterns and firing in conventional belt furnace. The detailed performance parameters, reflectance and EQE of the cells will be illustrated in the paper. In addition, free energy loss analysis and computer simulations of the cells will be performed using control parameters measured during the fabrication processes. 

Tokyo City University, Japan

Major Research Accomplishment in 5 Years of "FUTURE -PV Innovation" Project”

The author's group is currently developing methods to dramatically improve efficiency of solar cells using existing Si technology. Started in July 2012, the "FUTURE -PV Innovation" project is underway as a 5-year project in Koriyama City, Fukushima Prefecture. The current conversion efficiency of Si solar cells is restricted by the Si energy bandgap (Eg = 1.1 eV). The optimum energy bandgap for converting solar energy into electricity is approximately 1.5 eV. In the FUTURE-PV Innovation project, the  energy bandgap of Si will be controlled to around 1.3-1.7 eV using the quantum confinement effect, which will be obtained using an Si nanowire/wall  structure. According to theoretical analysis, it will be possible to obtain an energy bandgap of 1.3-1.7 eV if an extremely fine wire/wall of several nm diameter/width can be produced. Further, the project aims to achieve an energy conversion efficiency exceeding 30% by preparing a tandem solar cell using a waidegap nanowire/wall solar cell and a Si heterojunction solar cell.  The research is being implemented using a system known as an industry-university consortium. The research system consists of three teams; Team 1: Super-high-quality Si crystal technology, Team 2: Fabrication process for silicon nanowire/wall and characterization, Team 3:  Nanowire/wall solar cells.  In the presentation, research targets and recent major accomplishment will be demonstrated. 

Norwegian Research Centre for Sustainable Solar Cell Technology, Norway

Abstract to be uploaded soon.

Fraunhofer ISE, Germany

Silicon solar cells with full-area passivated rear contacts: Influence of wafer resistivity on device performance on a 25% efficiency level

Screen-printed Al-BSF silicon solar cells have dominated the PV market for decades. One of the advantages of the Al-BSF cells is the simple one-dimensional current flow pattern in the base resulting in high fill factors. R&D at Fraunhofer ISE aims at realizing such a 1D structure by applying a passivated contact scheme consisting of a tunnel oxide covered by a heavily doped silicon film, called TOPCon. A champion efficiency of 25.1% on n-type silicon was presented in the past showing the high potential of this technology. In particular, the high fill factors above 83% obtained on these cells are a result of the 1D current flow pattern. In this presentation we focus on the influence of the wafer resistivity on the performance of such cells on a 25% efficiency level. For this purpose we have fabricated both sides contacted solar cells with the TOPCon rear contact using n-type silicon wafer with different resistivities.

Institute for Solar Energy Research Hamelin (ISFH), Germany

Recent advances in understanding and suppressing light-induced degradation in multi-Si solar cells

The prevalent material used in today’s world-wide solar cell production is block-cast multicrystalline silicon (multi-Si). In order to further enhance the efficiency, an increasing number of cell manufacturers are currently upgrading their cell lines from the standard Al-BSF to PERC-type processes with Al2O3/SiNx rear-surface passivation. Unfortunately, multi-Si PERC cells seem to be prone to a pronounced light-induced degradation (LID) effect under typical module operating conditions. In this contribution, we give an overview of the current state of knowledge of this phenomenon, discussing LID experiments performed by several companies and institutes on wafers, cells and modules. In addition, the current level of fundamental understanding and potential loopholes are presented.

University of New South Wales, Australia

Advanced hydrogenation of mono-Si solar cells

New techniques for the hydrogen passivation of defects and contaminants in crystalline silicon have focused on the control of the charge state of the hydrogen atoms to greatly enhance the diffusivity and reactivity. It appears most forms of recombination can be passivated, particularly the boron-oxygen defects apparently responsible for light-induced degradation (LID) in p-type Cz wafers. The new passivation techniques have been applied to cells from PERC production lines belonging to eight separate manufacturers, with an average performance increase of 5% with minimal subsequent LID during light-soaking. Perhaps surprisingly, the recent study and apparent identification of the defect in multi wafers responsible for typically 10% LID, has led to the identification of the same defect in mono silicon, including Cz and FZ, and both p-type and n-type wafers. Passivation techniques for this defect also appear to have been developed.