Page 28 - RSE - Results of the Apollon Project

Results of the APolloN PRoject ANd coNceNtRAtiNg PhotovoltAic PeRsPective

Main Achievements in III-V MJ High Effciency Solar Cells,
a Comparison with State of the Art

III-V based solar cells have been developed both for Mirror based and Fresnel based systems. In the frst phase
of the project, ENE developed Single junction (SJ) InGaP and dual junction (DJ) InGaP/GaAs solar cells customized
for the “high energy gap” target of the Mirror Based Spectrum Splitting system. The development of TJ solar cells
involved several research activities according to the diagram shown in Figure 19.

FiguRE 19. Block diagram of the different research activities carried out under APOLLON to increase the cell
economic performance index value of III-V based solar cells

Advanced MJ solar cells
WP2

Fabrication of ge substrates Mj cells development Low temperature ge development of a new high
WP 2.1 WP 2.2 and Sige epitaxy fexibility MOCvd
WP 2.3 growth chamber
WP 2.3

tj @ 750 X tj with New
task 2.2.2 Concepts
task 2.2.5

While the description of the development of a new high fexibility MOCVD growth chamber (WP2.4) for high
effciency and high yield MJ solar cells has been already outlined in the previous chapter, the following section will
describe the activities carried out on the MJ development (WP 2.2) and on low temperature Ge and SiGe epitaxy (WP2.3).

tj at high concentration

The goal of the industrial Partner ENE was to customize the solar cells for the CPV system suppliers, and in case
of MJ solar cells, trying optimizing the solar cells with high performing tunnel diodes, in order to increase the CEPI
value. The performance values obtained are shown in Table 4.

tABLE 4. Performance of the III-V solar cells produced by ENE for Mirror Based Spectrum Splitting and Fresnel based
CPV systems

Cell type diA EFF (%) Concentration factor Yield (%)
InGaP/InGaAs DJ 29.2 750 78
InGaP/InGaAs/Ge TJ 35.5 750 78.8

In spite of the fact that DJ solar cells have only one tunnel diode, while TJ ones have two, it was demonstrated
that both devices can work at high concentration factor. Furthermore, considering that the manufacturing costs,
as well as the yield, are comparable for both devices, it has been shown that TJs are preferable over DJs for more
competitive CPV systems, since it is possible to get a higher value of the CEPI. TJ solar cells have been characterized
up to 4000 suns, showing an excellent effciency of 35,3% @ 2000 suns (see Figure 20).

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