Substrates, contacts and monolithic integration

Solar Energy Materials and Solar Cells, 1997

Although silicon solar cells based on layers less than 50 Ixm thick have become very popular, little attention has been paid to the role of the underlying silicon substrate. This treatment uses the device simulation program PC-1D and the ray tracing program SUNRAYS to examine the role of the substrate in contributing to the current and efficiency of textured and non-textured thin layer solar cells. For the case of a heavily doped silicon substrate, substrate contributions can be significant for cells with sufficiently thin base layers. For example, for the case of a silicon thin layer cell with a base layer thickness of 20 Ixm and a substrate doping of 6 X 10 ]8 cm-3, the substrate contributes no more than 4% of the total short-circuit current. However, decreasing the base width to 5 I~m results in an increase in this substrate contribution to 20%. Light trapping tends to alleviate the substrate contribution by increasing the effective path length in the base. Examination of the current components under forward bias reveals that for a thin layer cell with a high quality base and good front surface passivation, back diffusion of electrons into the substrate limits cell performance.

Progress in photovoltaics, 2004

o The different thin film technologies o Market share of thin film technologies o The record efficiencies of thin film technologies o Quantity of needed active material o The manufacturing

2000

online ordering: http://www.ntis.gov/ordering.htm Printed on paper containing at least 50% wastepaper, including 20% postconsumer waste i Summary The overall mission of the Institute of Energy Conversion is the development of thin film photovoltaic cells, modules, and related manufacturing technology and the education of students and professionals in photovoltaic technology. The objectives of this 20 month NREL subcontract are to advance the state of the art and the acceptance of thin film PV modules in the areas of improved technology for thin film deposition, device fabrication, and material and device characterization and modeling, relating to solar cells based on CuInSe 2 and its alloys, on a-Si and its alloys, and on CdTe.

Approximately half the cost of a "nished crystalline silicon solar module is due to the silicon itself. Combining this fact with a high-e$ciency potential makes thin-"lm crystalline silicon solar cells a growing research area. This paper, written in two parts, aims to outline world-wide research on this topic. The subject has been divided into techniques which use native substrates and techniques which use foreign substrates. Light trapping, vapour-and liquid-phase deposition techniques, cell fabrication and some general considerations are also discussed with reference to thin-"lm cells.

Progress in Photovoltaics: Research and Applications, 2006

Thin film solar cells (TFSC) have passed adolescence and are ready to make a substantial contribution to the world's electricity generation. They can have advantages over c-Si solar modules in ease of large area, lower cost manufacturing and in several types of applications. Factors which limit TFSC module performance relative to champion cell performance are discussed along with the importance of increased throughput and yield. The consensus of several studies is that all TFSC can achieve costs below 1 $/W if manufactured at sufficiently large scale >100 MW using parallel lines of cloned equipment with high material utilization and spray-on encapsulants. There is significant new commercial interest in TFSC from small investors and large corporations, validating the thin film approach. Unique characteristics are discussed which give TFSC an advantage over c-Si in two specific markets: small rural solar home systems and building integrated photovoltaic installations. TFSC have outperformed c-Si in annual energy production (kWhrs/kW), have demonstrated outdoor durability comparable to c-Si and are being used in MW scale installations worldwide. The merits of the thin film approach cannot be judged on the basis of efficiency alone but must also account for module performance and potential for low cost. TFSC advocates should promote their unique virtues compared to c-Si: lower cost, higher kWhr/kW output, higher battery charging current, attractive visual appearance, flexible substrates, long-term stability comparable to c-Si, and multiple pathways for deposition with room for innovation and evolutionary improvement. There is a huge market for TFSC even at today's efficiency if costs can be reduced. A brief window of opportunity exists for TFSC over the next few years due the Si shortage. The demonstrated capabilities and advantages of TFSC must be proclaimed more persistently to funding decision-makers and customers without minimizing the remaining challenges.

Materials, 2016

The trade-off between transmittance and conductivity of the front contact material poses a bottleneck for thin film solar panels. Normally, the front contact material is a metal oxide and the optimal cell configuration and panel efficiency were determined for various band gap materials, representing Cu(In,Ga)Se 2 (CIGS), CdTe and high band gap perovskites. Supplementing the metal oxide with a metallic copper grid improves the performance of the front contact and aims to increase the efficiency. Various front contact designs with and without a metallic finger grid were calculated with a variation of the transparent conductive oxide (TCO) sheet resistance, scribing area, cell length, and finger dimensions. In addition, the contact resistance and illumination power were also assessed and the optimal thin film solar panel design was determined. Adding a metallic finger grid on a TCO gives a higher solar cell efficiency and this also enables longer cell lengths. However, contact resistance between the metal and the TCO material can reduce the efficiency benefit somewhat.

2009

IEEE Transactions on Electron Devices, 2010

Monolithic interconnected modules are large-area high-voltage photovoltaic devices that are realized through solar cell segments that are series-connected via interconnection trenches during wafer processing. This paper investigates different processing techniques, giving detailed information about each processing sequence. In the first approach, a wet chemical etching procedure and photo-defined polyimide as dielectric film is used, leading to minimal trench width of 86 µm. Furthermore, we examine the applicability of advanced processing techniques. An alternative dry-etching process using reactive ion etching in inductively coupled plasma is investigated. With this technique, smooth and near-vertical sidewalls could be achieved, whereas the undercuts in etching profile, which are inevitable when using wet chemical etching, could be avoided. Moreover, an accurate processing technique for plasma-enhanced chemical vapor deposited SiN x as a dielectric film for electrical isolation is presented. This allowed sufficient isolation to be achieved, as well as enabling precise structuring. With these advanced processing techniques, trench widths of 57 µm were realized, resulting in a reduction of area losses due to interconnection from 9% to below 6%.

Science, 1999

The advantages and limitations of photovoltaic solar modules for energy generation are reviewed with their operation principles and physical efficiency limits. Although the main materials currently used or investigated and the associated fabrication technologies are individually described, emphasis is on silicon-based solar cells. Wafer-based crystalline silicon solar modules dominate in terms of production, but amorphous silicon solar cells have the potential to undercut costs owing, for example, to the roll-to-roll production possibilities for modules. Recent developments suggest that thin-film crystalline silicon (especially microcrystalline silicon) is becoming a prime candidate for future photovoltaics.

Next Generation Multilayer Graded Bandgap Solar Cells, 2018

This chapter presents the characterisation of solar cell devices fabricated using the pre-characterised ZnS, CdS and CdTe layers as documented in Chaps. 3, 4 and 5. For the fabricated PV devices as presented in this book, ZnS was used as the buffer layer, CdS is utilised as the window layer, while CdTe is utilised as the main absorber layer in forming the solar cell structure. Thus, the main solar cell structure explored incorporates a CdS/CdTe heterojunction core. This chapter systematically reports the effect of the incorporation of a buffer layer to base CdS/CdTe configuration and the effect of various window layer conditions on the device properties of PV devices. This is followed by the exploration of the effect of different conditions of CdTe absorber layer and post-growth treatment of the device properties. Further to this, the effect of the extrinsic doping of CdTe, metal contacts, various heat treatment temperatures, etching and the incorporation of pinhole plugin layers into the CdS-/ CdTe-based PV devices was also discussed (see Fig. 1.6).