Metamorphic GaInP-GaInAs Layers for Photovoltaic Applications

Abstract

GaxIn1−xAs and GayIn1−yP layers were grown lattice mismatched to GaAs and Ge by low-pressure metal organic vapor phase epitaxy (LP-MOPVE). These materials are very promising for further increasing the efficiency of monolithic triple-junction solar cells. Different buffer layer structures were realized. Transmission electron microscopy and x-ray diffraction analysis were used to characterize the quality of the crystal. Both linear and step-graded buffers in GaxIn1−xAs were successfully used under an active solar cell structure. GayIn1−yP as buffer material showed a worse performance. Excellent solar cell performance was achieved for lattice mismatched single-, dual- and triple-junction solar cells.

Light trapping, a new approach to spectrum splitting

“…To achieve high efficiencies for these cells, the lattice match conditions have to be regarded. Currently, new technologies like lattice mismatched and metamorphic cells [2] are developed though that alters this limitation. Furthermore, between cells tunnel diodes have to be inserted because the cells have opposite polarity.…”

Current-matched triple-junction solar cell reaching 41.1% conversion efficiency under concentrated sunlight

“…However, the nearly ideal combination of Ga 0.35 In 0.65 P, Ga 0.83 In 0.17 As, and Ge with band gap energies of 1.67, 1.18, and 0.66 eV causes a high lattice-mismatch of 1.1% between the Ge and the upper two subcells. This metamorphic cell structure ͑MM2͒ was developed at Fraunhofer ISE, 8,[10][11][12] and is investigated in this paper. To overcome the high mismatch of the materials, we have developed an optimized step-graded buffer structure made from Ga 1−y In y As.…”

Evaluating the effect of dislocation on the photovoltaic performance of metamorphic tandem solar cells

“…As known in the heteroepitaxial growth, while growing the proper buffer layer with adequate thickness above the bottom cell, it would accommodate most of the lattice misfit between the subsequent layers and bottom cell by the formation of MD in the buffer region [4,[25][26][27][28]. Thus, generation of the MD could be possibly avoided in the top and middle cells to the greatest extent.…”

“…However, in practice, under the influence of the misfit strain, a short (<L/2) or long MD line (>L/2) could be generated by the movement of the threading segments. For instance, if the length of the misfit segments shortens (<L/2), resulting from the change of buffer structure or external growth conditions [27], there is more TDD existing in the subsequent films according to eq. (6).…”