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CdTe vs. Crystalline Silicon Panels: Benefits & Applications

Crystalline silicon (c-Si) solar panels, either monocrystalline or polycrystalline panels, are the dominant panel technology, widely adopted from residential to C&I projects.

However, a newer panel type that has a distinct appearance from traditional c-Si panels began gaining traction in the market over the past decade or two. It is the CdTe solar panel technology.

This article will discuss the difference between CdTe and c-Si solar panels in composition, structure, benefits, applications, and more. Then in turn you will better comprehend CdTe.

Recapping Crystalline Silicon Panels (c-Si)

As a well-established and efficient technology, c-Si panels come in two main variants, monocrystalline and polycrystalline. The silicon material of the former is made from a single crystalline structure while the latter is made from multiple silicon crystals melted together. Apart from silicon, doping elements, usually phosphorus (P) and boron (B) are added to create the n-type and p-type semiconductor layers for energy conversion.

In addition to the photovoltaic layer, a typical c-Si panel also comprises electrical contacts and more to form a complete structure. Here are the layers, from top to bottom:

  • Front Cover
  • Encapsulation
  • Front Contact
  • c-Si Cell Layer
  • Back Contact
  • Encapsulation
  • Backsheet
  • Frame

Since the material and cutting process vary, c-Si panels can have different looks. In general, monocrystalline panels are characterized by a dark, uniform color and octagonal-shaped cells, with a smooth, consistent texture. In contrast, polycrystalline panels have a blue, speckled look and square cells, with a less consistent texture.

Despite the differences, both c-Si panel variants have visible thin metallic grid lines on the front, which are used to collect and carry the electric current generated by the cells.

Introducing CdTe Panel Technology

Cadmium Telluride (CdTe) solar panels opt for non-silicon materials in their photovoltaic layer. Therein, it comprises two parts:

  • Cadmium Sulfide (CdS) Layer: It acts as a window or buffer layer. This n-type layer allows sunlight to pass through with minimal absorption while facilitating efficient charge separation and collection.
  • Cadmium Telluride (CdTe) Layer: This layer is the primary absorber of sunlight. It converts photons into electron-hole pairs, which are then separated by the electric field at the p-n junction.

Compared to c-Si panels, a typical CdTe panel structure comprises: 

  • Encapsulation/Cover
  • Transparent Conductive Oxide (TCO) Layer: This is the front contact layer that allows light to pass through while conducting electricity.
  • Photovoltaic Layer
  • Back Contact: This layer collects the electrons generated and provides an electrical connection for the external circuit.
  • Substrate: It provides structural support and protection to the upper layers. This layer can be made of glass or flexible materials according to applications.

In contrast to c-Si panels, which feature individual cell units and visible front metal contacts, CdTe panels boast a modern, uniform appearance due to their continuous material composition.

Diagram: Different Layers of a Cadmium Telluride (CdTe) Solar Panel
Source: NREL

Benefits of CdTe Solar Panels

Besides an enhanced visual appeal, several other benefits of CdTe solar panels are also contributing to their growing popularity.

Cost-Effectiveness

Ongoing technological advancements and economies of scale have led to a big decline in the prices of traditional c-Si solar panels.

Currently, this technology costs from around $0.30 to $0.70 per watt or slightly more.

However, since fewer materials and energy are used in the manufacturing of CdTe panels, their average cost is even lower, ranging from $0.20 to $0.35 per watt.

Low Temperature Coefficient

The efficiency of most panels will be reduced as the environmental temperature increases.

Traditional c-Si panels have a temperature coefficient of anywhere between -0.3%/°C and -0.5%/°C depending on the materials used and technologies incorporated.

In CdTe technology, the figure of this metric can fall within the range of -0.20%/ºC to -0.30%/ºC. This supports a smoother energy conversion for the panels.

Superb performance In Low-Light Conditions

CdTe solar panels have a high absorption coefficient and can effectively utilize a broader spectrum of light, including wavelengths that are less intense which is common in scenarios such as cloudy days or early morning. This enables CdTe panels to generate power more effectively in less-than-ideal lighting conditions.

Increased Versatility and Flexibility

The absorption layer of c-Si panels is around 180 µm in thickness. In comparison, the thickness of CdTe panels only ranges from 1-6 μm1, mainly due to the high optical absorption coefficient and direct bandgap property of the semiconductor material. Studies have shown that 1 µm of some enhanced CdTe material is sufficient to absorb about 90% of the incident spectrum.

This strength indicates that in addition to being sandwiched between rigid tempered glass, CdTe technology can be manufactured with flexible thin-film substrates and covers. The flexible design can be applied to BIPV projects and is adaptive to a broader range of surfaces.

Potentially Shorter Payback Time

In spite of that at this moment the efficiency of CdTe solar panels cannot beat that of traditional c-Si panels, their lower cost, shorter energy payback time (EPT), low temperature coefficient and excellent performance in low-light conditions make them ideal for particular projects, potentially leading to a shorter payback time.

What Are the Common Applications of CdTe Solar Panels?

As a mature, well-established technology, mono- and poly-crystalline solar panels can be adopted in a multitude of solar projects.

Despite ongoing improvements, CdTe solar panels have been most extensively applied in the following project types.

Utility-Scale Solar Power Plants

The lower cost of CdTe solar panels compared to c-Si panels makes them an attractive option for utility-scale installations where space is not a critical constraint.

Leveraging the benefits of scale in utility-scale plants, their exceptional temperature coefficient and absorption coefficient are helpful to compensate for their moderately lower efficiency. This further yields quite decent solar production and shortens payback time.

BIPV Projects

With a modern, uniform appearance as well as a thickness of just several μm, CdTe technology can be well customized and adaptive to building materials like facades, windows and skylights.

These features make them particularly good fits for aesthetically sensitive applications.

Commercial and Industrial (C&I) Installations

CdTe panels can also be used in commercial and industrial settings. Their adaptability to different structures and lower costs in comparison to c-Si technologies make them ideal for large rooftops and other commercial applications.

They are often chosen for installations where the initial cost is a significant consideration.

Extreme Hot Climates & Low-Light Conditions

In sites with extreme hot climates or low-light conditions, CdTe solar panels can offer a more suitable alternative to traditional c-Si panels. They provide stable energy output and are geared toward long-term performance.

Outlook for CdTe and Crystalline Silicon Technologies

As of now, the main weak point of CdTe technology is their comparatively lower efficiency. As a consequence, researchers are actively engaged in investigating material science and manufacturing technology to optimize the efficiency of CdTe panels.

Furthermore, efforts are being made to refine the treatment and recycling of less environmentally-friendly elements such as cadmium to alleviate concerns and facilitate the adoption of this technology.

On the other hand, efforts are also being directed towards refining traditional c-Si panel technology. Beyond improving current c-Si panel manufacturing methods such as HJT, PERC, IBC, shingled and half-cut, newer techniques such as perovskite-crystalline silicon tandeming and layer transferring are being developed to take the performance of c-Si panels to the next level.

Conclusion

On the whole, in the foreseeable future, CdTe solar panels emerge as a good pick for budget-constrained projects and those that demand marked performance for particular metrics.

c-Si panels are a well-proven solar technology and suitable for an extensive range of projects, but with advanced variants being more expensive.

  1. Cu-doped CdS and its application in CdTe thin film solar cell (Deng et al., 2016) ↩︎

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