High-efficiency dual-junction GaInP/GaAs tandem solar cells obtained by the method of MOCVD
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High-Efficiency Dual-Junction GaInP/GaAs Tandem Solar Cells Obtained by the Method of MOCVD V. M. Lantratov^, N. A. Kalyuzhnyœ, S. A. Mintairov, N. Kh. Timoshina, M. Z. Shvarts, and V. M. Andreev Ioffe Physicotechnical Institute, Russian Academy of Sciences, Politekhnicheskaya ul. 26, St. Petersburg, 194021 Russia ^e-mail: [email protected] Submitted October 30, 2006; accepted for publication November 7, 2006
Abstract—Monolithic dual-junction GaInP/GaAs solar cells grown by the MOCVD method were studied. The conditions of the growth of ternary GaxIn1 – xP and AlxIn1 – xP alloys lattice-matched to GaAs are optimized. Technology for fabrication of a tunneling diode with a high peak current density of 207 A/cm2 on the basis of heavily doped n++-GaAs:Si and p++-AlGaAs:C layers is developed. Cascade GaInP/GaAs solar cells obtained as a result of relevant studies featuring a good efficiency of the solar-energy conversion both for space and terrestrial applications. The maximum value of the GaInP/GaAs solar-cell efficiency was 30.03% (at AM1.5D, 40 suns). PACS numbers: 84.60.Jt, 81.15.Gh DOI: 10.1134/S106378260706022X
1. INTRODUCTION Progress in the development of solar-power engineering is related to the fabrication of monolithic multiple-junction (cascade) solar cells based on the III–V semiconductor compounds. Increasing the number of p–n junctions in cascade solar cells makes it possible to appreciably extend the region of photoactive absorption of solar radiation and reduce the energy losses characteristic of single-junction solar cells. The first AlGaAs/GaAs monolithic dual-junction solar cells were fabricated in 1985 [1] owing to the development of the MOCVD technology. In spite of a high theoretical limit for the conversion efficiency (in excess of 35%) for this combination of materials for cascade solar cells, Hutchby et al. [1] failed to attain a high conversion efficiency as a result of the high concentration of defects related to the active interaction of oxygen with AlGaAs and also to the difficulty encountered with fabrication of an effective and stable tunneling diode. The further development of monolithic dualjunction cascade solar cells is related to the use of the Ga0.52In0.48P/GaAs pair of materials [2–6]. Studies of these solar cells made it possible to fabricate GaInP/GaAs solar cells with unprecedentedly high efficiencies of 30.3% (AM1.5G) [5] and 27.2% (AM0.1 sun) [6]. MOCVD technology for the fabrication of high-efficiency single-junction solar cells with internal Bragg reflector based on AlGaAs/GaAs [7–9] has been under development at the Ioffe Physicotechnical Institute since the beginning of the 1990s. Active studies concerned with the fabrication of monolithic multiplejunction solar cells started in 2004 as the AIX-200/4
system for MOCVD was set into operation. This publication is concerned with the study and development of technology for the fabrication of GaInP/GaAs cascade solar-cell structures. 2. EXPERIMENTAL The solar-cell structures were grown using
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