Potential and present status of III–V/Si tandem solar cells

Abstract

III-V compound and Si tandem solar cells are expected to have great potential of space and terrestrial application because of high efficiency, light weight and low cost potential. However, problems to be solved are high density of dislocations and large residual strain in III-V compound on Si in the case of hetero epitaxy of III-V compound materials on Si substrates. There are other approaches such as epitaxial lift-off and direct bonding technologies in order to prevent such problems. This paper presents efficiency potential of III-V/Si tandem solar cells and effects of dislocation upon solar cell properties of III-V-on-Si single-junction solar cells and III-V/Si tandem solar cells. The paper also reviews approaches on reduction in dislocation density in III-V compound films on Si and improvements in efficiencies of 111-V compound single junction solar cells on Si substrates and III-V/Si tandem solar cells. We have demonstrated 20% efficiency (under I-sun of AM1.5G) with hetero-epitaxially grown GaAs single-junction solar cells on Si and Ohio State University has also demonstrated 17.1 % (AMO) efficiency with GaAs single-j unction solar cells by using Ge buffer layer. Nagoya Inst. Tech. has achieved 22.1% with GaAs/Si tandem solar cell by hetero epitaxy. Most recently, Fraunhofer ISE has demonstrated 27.9 % efficiency (under 48.3-suns of AM1.5D) InGaP/GaAs/Si 3-junction solar cells by using epitaxial lift-off and direct bonding. Future prospects are also discussed. Index Terms -III-V/Si tandem solar cells, hetero-epitaxy of III-V compounds on Si, dislocation behavior, minority carrier lifetime, solar cell properties.

III–V Multijunction Solar Cell Integration with Silicon: Present Status, Challenges and Future Outlook

“…One of the inherent benefits of using step-graded Si x Ge 1-x buffer is the ability to realize high-quality, low TDD and relaxed Ge layers on Si substrate providing a "virtual" Ge platform for subsequent GaAs growth (Currie et al 1998). (Ohmachi et al 1988) , reprinted with permission from Yamaguchi (2014) and Ohmachi et al (1988). Reference Yamaguchi (2014) Copyright 2014, IEEE; Ohmachi et al (1988).…”

III–V Multijunction Solar Cell Integration with Silicon: Present Status, Challenges and Future Outlook

“…Additionally, thin strained layers (SLs) and superlattices introduced into the bulk GaAs buffer have been shown to facilitate the annihilation of TDs and minimize the dislocation propagation into the active layers of interest. Such an approach led to one of the highest efficiencies for heteroepitaxial 1J GaAs-on-Si solar cells (Ohmachi et al 1988;Yamaguchi 2014). More recent approaches involve the growth of metamorphic graded buffers (e.g.…”

“…An initial 10-to 15-nm thick low temperature GaAs was grown at 400˚C, followed by the subsequent growth of~2-µm thick GaAs at 700˚C. Five iterations of TCA were performed at 900˚C, followed by the growth of five periods of In 0.1 Ga 0.9 As/GaAs (10 nm/10 nm) SLS and five periods of Al 0.6 Ga 0.4 As/GaAs (20 nm/100 nm) SL, prior to the growth of 1J p/n GaAs solar cell structure (Ohmachi et al 1988;Yamaguchi 2014). The 1J GaAs-on-Si solar cells realized using the combination of TCA, SLS and SL buffer demonstrated an efficiency of 20% under AM1.5g and 18.3% under AM0 conditions (at a TDD of~4.5 Â 10 6 cm −2 ), both of which are the highest efficiencies reported for heteroepitaxial 1J GaAs-on-Si solar cells (Ohmachi et al 1988;Yamaguchi 2014).…”

“…One of the inherent benefits of using step-graded Si x Ge 1-x buffer is the ability to realize high-quality, low TDD and relaxed Ge layers on Si substrate providing a "virtual" Ge platform for subsequent GaAs growth . (Ohmachi et al 1988) , reprinted with permission from Yamaguchi (2014) and Ohmachi et al (1988). Reference Yamaguchi (2014) Copyright 2014Ohmachi et al (1988).…”

“…(Ohmachi et al 1988) , reprinted with permission from Yamaguchi (2014) and Ohmachi et al (1988). Reference Yamaguchi (2014) Copyright 2014Ohmachi et al (1988). Copyright 1988, Cambridge University Press.…”