Abstract
The integration of III–V and Si multi-junction solar cells as photovoltaic devices has been studied in order to achieve high photovoltaic conversion efficiency. However, large differences in the coefficients of thermal expansion and the lattice parameters of GaAs, Si, and InGaAs have made it difficult to obtain high-efficiency solar cells grown as epilayers on Si and InP substrates. In this paper, two types of devices, including GaInP/GaAs stacked on Si (GaInP/GaAs//Si) and GaInP/GaAs stacked on InGaAs (GaInP/GaAs//InGaAs), are fabricated via mechanical stacking and wire bonding technologies. Mechanically stacked GaInP/GaAs//Si and GaInP/GaAs//InGaAs triple-junction solar cells are prepared via glue bonding. Current-voltage measurements of the two samples are made at room temperature. The short-circuit current densities of the GaInP/GaAs//Si and GaInP/GaAs//InGaAs solar cells are 13.37 and 13.66 mA/cm2, while the open-circuit voltages of these two samples are measured to be 2.71 and 2.52 V, respectively. After bonding the GaInP/GaAs dual-junction with the Si and InGaAs solar cells, the conversion efficiency is relatively improved by 32.6% and 30.9%, respectively, compared to the efficiency of the GaInP/GaAs dual-junction solar cell alone. This study demonstrates the high potential of combining mechanical stacked with wire bonding and ITO films to achieve high conversion efficiency in solar cells with three or more junctions.
Highlights
It is well known from theoretical simulation results that tandem-type III–V material multi-junction solar cells have higher conversion efficiency than solar cells constructed using other materials[1,2]
An increase in Voc could contribute more to the efficiency of a TJ solar cell than an increase in Jsc. This shows that wire bonding and mechanical stacking are useful for increasing the conversion efficiency of multi-junction solar cells
GaInP/GaAs//Si and GaInP/GaAs//InGaAs triple-junction (TJ) solar cells were successfully fabricated via mechanical stacking and wire bonding
Summary
It is well known from theoretical simulation results that tandem-type III–V material multi-junction (with six junctions) solar cells have higher conversion efficiency than solar cells constructed using other materials[1,2]. A high conversion efficiency of over 30% under the one-sun air mass 1.5 (AM1.5G) spectrum condition has been achieved using GaInP/GaAs/Ge triple-junction (TJ) solar cells[14], the cost of such a device is high because the underlying Ge substrate is very expensive. Www.nature.com/scientificreports phase epitaxy (MOVPE) is challenging[17] because of large differences between the thermal expansion coefficients[17] and a 4% lattice mismatch[17] between Si and the most common III–V layers that are lattice-matched to GaAs. multi-junction solar cells are instead fabricated using the mechanical bonding method[4,5,6]. The mechanical stacking technologies that can be used to fabricate multi-junction solar cells include glue-, metal-, and fusion-bonding[18,19,20,21,22]. TCO electrodes form an ohmic contact with the top contact layer of the solar cell, and enhance the performance of solar cells thanks to the highly transparent layer
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