Sachin Surve

Monolithic perovskite/silicon-homojunction tandem solar cell with over 22% efficiency

Crystalline silicon (c-Si) solar cells featuring a high-temperature processed homojunction have dominated the photovoltaic industry for decades, with a global market share of around 93%. Integrating commercially available crystalline silicon solar cells with high-efficiency perovskite solar cells is a viable pathway to increase the power conversion efficiency, and hence achieve low levelized electricity costs for the photovoltaic systems. However, the fabrication process for this type of cell is challenging due to the many, and often conflicting, material processing requirements and limitations. Here, we present an innovative design for a monolithic perovskite/silicon tandem solar cell, featuring a mesoscopic perovskite top subcell and a high-temperature tolerant homojunction c-Si bottom subcell. The improved temperature tolerance of the c-Si bottom cell permits significantly increased flexibility in the design and fabrication of the perovskite cell. We demonstrate an efficiency of 22.5% (steady-state) and a Voc of 1.75 V on a 1 cm2 cell. The method developed in this work opens up new possibilities in designing, fabricating and commercialising low-cost high-efficiency perovskite/c-Si tandem solar cells.

A 20-sun hybrid PV-Thermal linear micro-concentrator system for urban rooftop applications

A unique, linear, low-concentration, hybrid ‘micro-concentrator’ (MCT) system concept has been developed specifically for urban rooftop environments. The light-weight, low-profile form factor satisfies aesthetic demands for general rooftop solar technologies, and is a marked departure from conventional linear concentrator systems. Valuable thermal energy, normally of nuisance value only, and usually wasted by conventional CPV, is extracted via a heat transfer fluid. The recovered thermal energy can be used for applications ranging from domestic hot water through to space heating, ventilation, and air conditioning (HVAC), and process heat. The system can be modularly configured for hybrid concentrating PV-Thermal (CPV-T) or thermal-only operation to meet specific customer demands. At a 20x concentration ratio, system output of 500 Wpe and 2 kWpt is expected, for a combined system efficiency of up to 75%. The MCT is constructed from mature, proven technologies and industry-standard processes. An installed system cost of less than US

Characterization of Laser-Doped Localized p-n Junctions for High Efficiency Silicon Solar Cells

2/Wpe is targeted, and commercial availability is expected to commence in 2011.

Perimeter Recombination Characterization by Luminescence Imaging

To further increase the efficiency of industrial crystalline silicon solar cells, a point-contact solar cell concept with localized p-n junctions is considered a promising candidate if implemented by a low cost processing technique like laser doping. For efficient development and optimization of such a processing technique, we present a dedicated test structure to derive the fundamental diode characteristics specific to the localized p-n junction, namely the contact resistance to the metal and the recombination properties, i.e., the dark saturation current. Those properties are fitted to measured dark current-voltage curves by 3-D device simulations using Quokka. We show that in particular, the contact resistance can be accurately extracted and that the method is robust against uncertainties of other device properties of the test structure. Simulations of an idealized point-contact solar cell are performed to judge the usefulness of the extractable value range with respect to the efficiency potential. Furthermore, we apply the method to laser doping experiments. We successfully characterize the recombination and contact resistance and identify a ~24% efficiency potential of a nonoptimized two-step laser doping process. Other single step processes show a very high recombination (J0pn ≫ 1e-10 A/cm2) likely due to imperfections around the perimeter of the laser processed area.

Untangling the Mysteries of Plated Metal Finger Adhesion: Understanding the Contributions From Plating Rate, Chemistry, Grid Geometry, and Sintering

Perimeter recombination causes significant efficiency loss in solar cells. This paper presents a method to quantify perimeter recombination via luminescence imaging for silicon solar cells embedded within the wafer. The validity of the method is discussed and verified via 2-D semiconductor simulation. We demonstrate the method to be sufficiently sensitive in that it can quantify perimeter recombination even in a solar cell where no obvious deviation from ideality is observed in the current-voltage (J-V) curve.

Characterizing the Influence of Crystal Orientation on Surface Recombination in Silicon Wafers

Historically, busbar pull tests have been used as a measure of metal-silicon adhesion for silicon solar cells; however, such measurements cannot be easily applied to evaluate finger adhesion and the propensity of metal fingers to peel. Finger adhesion will be increasingly important as the width of fingers decrease and busbars are effectively removed from the cell metallization. In this paper, we correlate metal-plated finger dislodgement measurements, which have been obtained using a stylus-based metallization testing tool, and busbar pull test forces with nanoindentation measurements of the Youngs modulus in order to determine key determinants of strong finger adhesion. It is proposed that metal fingers with a higher Youngs modulus dislodge at lower stylus impact forces because the energy associated with the impact is less easily dissipated along the fingers and consequently remains more focused on the impact location, causing not only finger dislodgement but more extensive finger peeling as well. It is shown how plating rate, chemistry, grid geometry, and postplating annealing can all contribute to plated metal finger adhesion, therefore necessitating an understanding of these factors for reliable plated metallization.

A Monolithic Microconcentrator Receiver For A Hybrid PV‐Thermal System: Preliminary Performance

We present two approaches for evaluating the influence of crystal orientation on surface passivation of silicon wafers using photoluminescence imaging. The methods allow a variety of orientations that are not limited to (1 0 0) and (1 1 1) planes to be studied. The first approach is based on imaging carrier lifetimes in silicon strips containing different surface orientations that have been created from a single monocrystalline silicon wafer via laser cutting. The second approach is based on imaging carrier lifetimes among different grains in multicrystalline silicon wafers, which make use of their random distribution of crystal orientations. Both approaches are demonstrated with silicon-oxide-passivated samples. The results from both methods are consistent with each other, showing that the studied silicon oxide films provide a better passivation on surfaces with higher surface energy, such as (1 0 0) or (1 0 6) surfaces, compared with those with lower surface energy, such as (2 3 5) or (1 1 1) surfaces. The advantages and limitations of both approaches are also discussed and compared.

Evaluation Of Electrical And Thermal Performance Of A Linear Hybrid CPV‐T Micro‐Concentrator System

An innovative hybrid PV‐thermal microconcentrator (MCT) system is being jointly developed by Chromasun Inc., San Jose, California, and at the Centre for Sustainable Energy Systems, Australian National University. The MCT aims to develop the small‐scale, roof‐top market for grid‐integrated linear CPV systems. A low profile, small footprint enclosure isolates system components from the environment, relaxing the demands on supporting structures, tracking, and maintenance. Net costs to the consumer are reduced via an active cooling arrangement that provides thermal energy suitable for water and space heating, ventilation, and air conditioning (HVAC) applications. As part of a simplified, low‐cost design, an integrated substrate technology provides electrical interconnection, heat sinking, and mechanical support for the concentrator cells. An existing, high‐efficiency, one‐sun solar cell technology has been modified for this system. This paper presents an overview of the key design features, and preliminary el...

Designing CPV Receivers With Reliability: Early Evaluation of Components

Chromasun Inc. and The Australian National University have developed a low‐concentration, linear, hybrid micro‐concentrator (MCT) system suitable for urban rooftop installation. The system produces both electrical and thermal power, integrating the functionality of separate flat plate photovoltaic and solar hot water systems. The MCT system utilises industry‐standard components, including modified mono‐crystalline silicon one‐sun solar cells, commonly used in flat panel applications. The MCT manufacturing processes are designed around low‐cost methods, and tap directly into existing economies of scale. Initial test results without any system optimisation has demonstrated an electrical output of more than 300 W, and a thermal output of more than 1500 W at 950 W/m2 DNI.

Hybrid CPV-T micro-concentrator system

The Australian National University (ANU) is developing a new hybrid CPV/Thermal micro‐concentrator (MCT) system working at a concentration ratio of 20 to 30X. System design and reliability have been integrated as a concurrent process, enabling early optimisation of the concentrator design. The key feature of this procedure is that a carefully selected set of simple tests can be conducted concurrently with the design of the concentrator module, without introducing time delays on the module design. Test results provide valuable information that significantly informs the design process and helps to avoid future failures.