413 Materials Overview

In a typical crystalline silicon cell, the n layer is about 0.5 |im thick and the p layer is about 0.25 mm thick. The energy contained in a photon Ep is given by

Ep = hv where h is the Planck's constant (6.625 x 10-34 J-sec) and v is the frequency, which is related to the wavelength and the speed of light c by v = c/X

Therefore,

For silicon, which has a band gap of 1.11 eV, this expression shows that photons of solar radiation of wavelength 1.12 |im or shorter are useful in creating electron-hole pairs and, therefore, an electric current.

Table 4.1 lists some candidate semiconductor materials for PV cells along with their band gaps. Substances shown in bold type are promising PV materials.

TABLE 4.1

Energy Gap for Some Candidate Materials for Photovoltaic Cells

Material

Bandgap (eV)

Si

1.11

SiC

2.60

CdAs2

1.00

CdTe

1.44

CdSe

1.74

CdS

2.42

CdSnO4

2.90

GaAs

1.40

GaP

2.24

Cu2S

1.80

CuO

2.00

Cu2Se

1.40

CuInS2

1.50

CuInSe2

1.01

CuInTe2

0.90

InP

1.27

In2Te3

1.20

InA

2.80

Z%P2

1.60

ZnTe

2.20

ZnSe

2.60

AIP

2.43

AISb

1.63

As2Se3

1.60

Sb2Se3

1.20

Ge

0.67

Se

1.60

Figure 4.7 shows a comparison of the maximum energy conversion efficiency of cells for some of the listed materials. This figure shows that the optimum band gap for terrestrial solar cells is around 1.5 eV.

Solar Stirling Engine Basics Explained

Solar Stirling Engine Basics Explained

The solar Stirling engine is progressively becoming a viable alternative to solar panels for its higher efficiency. Stirling engines might be the best way to harvest the power provided by the sun. This is an easy-to-understand explanation of how Stirling engines work, the different types, and why they are more efficient than steam engines.

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