FIGURE 4 Device performance with partial rear
SrF2 films. (A) A sketch of the solar cells applying
SrF2 electron-selective contacts. (B-E)Voc , FF, Jsc , and PCE of
the device with various SrF2 thicknesses (nm). (F) LightJ–V characteristics of the device under AM1.5 conditions.
To evaluate the optical properties of SrF2 electron
selective contacts when applied on PERC structure solar cells. Figure 5A
depicts the characterized EQE, reflectance of the highest efficiency
device, and its relevance, with the measurements were taken between the
finger electrode.
Obviously, a considerably high integration Jsc of
the EQE of 42.30 mA∙cm-2 was achieved, surpassing theJsc value of the counterpart solar cell which was
41.32 mA∙cm-2. These findings are consistent with theJsc values obtained from the J-Vcharacterization discussed earlier. . The optical quality of the back
side can be indicated by the internal quantum efficiency (IQE) for
longer wavelengths (900 ~ 1200 nm). A higher IQE is
observed at wavelengths between 500 nm and 1200 nm for cells with
SrF2 interlayer than in the case of the cells only
metalized by Al backside. This maybe indicates that SrF2film increases the spectral response and light reflection at its
interfaces to the Si bulk, demonstrating the high electron selectivity
characteristics offered by the low WF SrF2/Al contacts.
The stability of PCE is an essential factor to consider when evaluating
the practical application of a solar cell. The champion samples were
surveyed and stored in an ambient atmosphere as shown in Figure 5B. The
PCE can remain constant for the first 168 hours at 21.5%. Then, a tiny
decline can be seen, but it is still close to 21% after 1000 hours. The
PCE was maintained at 17% to 17.5% even after samples were exposed to
the air for 5000 hours and 15000 hours. We identify several potential
causes for this phenomenon: (i) the increasing contact resistivity in
Figure 2b. and (ii) the advent of Al diffusion into the silicon
substrate of the electron-selective contact layer can lead to a
rectifying contact, as has been widely reported in the
literature.36,42 The stability of this structure could
be further enhanced after module encapsulation. The use of
SrF2 as DF-ECSCs presents significant potential for mass
manufacture due to its excellent PCE stability and high tolerance to
variations in thickness during fabrication.