Development of new materials for solar cells in Nagoya Institute of Technology

Abstract

Solar cells with high efficiency and low price have long been desired, however, the commercially available solar cells are still expensive and the efficiencies of them are not high enough yet. A tandem solar cell was fabricated to develop a high-efficiency solar cell, and amorphous carbon solar cells were fabricated to develop a low-price solar cell.An AlGaAs/Si tandem solar cell was successfully fabricated by heteroepitaxial growth of AlGaAs on Si substrate. At first, a p-n junction was formed in Si substrate by the impurity diffusion method. Then, an AlGaAs p-n junction was grown by MOCVD. Since the AlGaAs p-n junction has a graded band gap emitter, the photo-excited minority carriers can be collected efficiently. The energy conversion efficiency of AlGaAs/Si tandem solar cell was 21.4% (AM0) in spite of large lattice mismatch and difference in thermal expansion coefficients between AlGaAs and Si. Solar cells were fabricated by using amorphous carbon films deposited by Ion Beam Sputtering and Pulse Laser Deposition (PLD). The highest efficiency of 1.82% (AM0) was attained with a-C(IBS)/p-C(pyrolysis)/p-Si structure. Solar cells using a-C:H were also fabricated by PLD and Plasma CVD, and the efficiencies of them were 2.1% (AM1.5) and 0.04% (AM0), respectively.Other research activities on solar cells in Nagoya Institute of Technology are briefly mentioned. q

Preparation and Optoelectronic Properties of Cu2ZnSnS4Film

“…Although many efforts have been made on the developments of low-cost solar cells with high efficiency, the efficiency of solar cell is still low and the cost is still high. 1 Cu 2 ZnSnS 4 (CZTS) has been studied by some groups over the past years, [2][3][4] CZTS is considered as a good solar cell absorber with a high absorption coefficient above 10 4 cm −1 and is a direct band-gap semiconductor (E g = 1.4∼1.9 eV), 5,6 as an earth abundant, cheap, nontoxic alternative to other toxic and expensive compounds such as CdTe, CuInGa(S,Se) 2 (CIGS) and GaAs. According to photon balance calculations of Shockley-Queisser, the theoretical efficiency of CZTS solar cell is expected to be more than 30%.…”

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

“…Tech. group has demonstrated 21.2% (AMO) efficiency (Voc=1.S7 V, Jsc=23.6 mAlcm 2 , FF=77.2 %) has been realized with A0 1SGao8SAs/Si 2-junction solar cell by TCA [23]. Figure 10 shows AMO efficiency distribution of the solar cells with SO and 100 11m cover glass.…”

GaAsP single nanowire solar cells grown on silicon exhibiting large Voc increase at multiple suns

“…More than three decades of research into monolithic integration of III-V on silicon has been carried out without producing the resilient high quality planar layers needed to manufacture commercially viable structures. Specifically, the III-V on silicon dual-junction solar cell has been hampered by crystal defects caused by the incompatible material properties [3], [4]. The Ga(In)AsP III-V material system that is known for yielding the highest efficiency in multi-junction solar cells has with a GaAs 0.7 P 0.3 solar cell grown on silicon achieved the record conversion efficiency of only 9.8% [5].…”