Photoluminescence of solar cell materials

• Main Authors: Min-De Yang, 楊敏德
• Other Authors: Ji-Lin Shen
• Format: Others
• Language: en_US
• Online Access: http://ndltd.ncl.edu.tw/handle/97097623092419301223

博士 === 中原大學 === 應用物理研究所 === 97 === This dissertation is devoted to the electronic and optical properties of semiconductor solar cell materials. The materials investigated include the InN, γ-In2Se3, and InGaP/GaAs/Ge three junction solar cells. The first part of the dissertation is investigating the effect of InN epilayer grown on Si substrate with different buffer layers. The InN epilayer grown on three buffer layers has the best optical quality by studying the photoluminescence (PL) and time-resolved PL (TRPL). According to the x-ray diffraction (XRD) measurements and transmission electron microscopy (TEM), the strain has been reduced between the InN epilayer and the Si substrate by using three buffer layers. Therefore, the InN epilayer has the best structural quality by growing three buffer layers. In the second part, the energy relaxation of electrons in InN epilayers is studied using PL measurements. It is found the measured electron temperature variation in different concentration can be explained by a model based on the energy relaxation of electrons due to both longitudinal optical (LO) phonon and acoustics phonon scattering. Under 15 K, the InN phonon lifetime obtained from experiments is higher than that from the theoretical calculations. This deviation is attributed to the presence of the hot phonon effect. The third part describes that the single phase γ-In2Se3 epilayers and nanorods on Si substrates were successfully grown by the metalorganic chemical vapor deposition (MOCVD). According to the XRD, high-resolution transmission electron microscopy (HRTEM) and selected-area electron diffraction (SAED), we demonstrated the grown γ-In2Se3 is the single crystal structure. It is found that the emission of the LO-phonons is the main energy loss process for hot electrons in -In2Se3 epilayers. The Raman peak at 151 cm-1 in -In2Se3 can be assigned to the LO-phonon mode. In the last part, we studied the PL and time-resolved PL of three-junction InGaP/InGaAs/Ge solar cells following rapid thermal annealing (RTA) and the incorporation of Au nanoclusters. The improvement of material quality in the InGaP active layer after RTA is evident from the PL and spectral response. When the annealing temperature is 300 oC, the PL intensity and carrier lifetime is maximum, which are respectively increased by about a factor of 2 and 5 compared with that of the untreated sample. We suggest that the removal of the phosphorusvacancy-related complexes may be responsible for improvement of the material quality after RTA. The power conversion efficiency is creased by 2 % after the 300 oC RTA treatment. In addition, the PL intensity (decay time) of the InGaP active layer in the triple-junction solar cell is increased by 1.5 (6) times after incorporation of gold nanoclusters. Based on the Mie scattering, the scattering factors of the gold nanoclusters as a function of wavelength were calculated. It is found the experimental enhancement of luminescence as a function of wavelength is in good agreement with the calculated results from the Mie scattering. We therefore suggest that the scattering of the gold nanoclusters is responsible for the enhancement of luminescence.