非晶矽矽鍺合金作為薄膜太陽能電池吸收層:特性、最佳化以及元件特性之研究

Abstract

在本研究中，藉著改變氫流率、電漿功率、以及製程氣體和電極間距來研究非晶矽鍺薄膜特性以及太陽能發光效率。 製程氣體我們使用矽甲烷(SiH4)、鍺甲烷(GeH4)以及氫氣，利用 射頻電漿輔助化學氣相沉積系統(PECVD)來沉積非晶矽鍺薄膜。由本篇實驗發現通入適當氫氣可提升光電導，而鍺原子濃度亦影響光學能隙以及電性。電漿功率除了會影響薄膜沉積速率外同時亦可提升電性。在元件的表現來說，較高的Xg (Xg= GeH4 / (GeH4+SiH4)) 值讓的元件短路電流下降並造成太陽能電池的發光效率由6.33% 降低至4.85 %。

In this study, the effects of systematic variation in hydrogen dilution, RF power, gas phase ratio of germane (Xg), the electrode spacings (E/S) on the amorphous silicon germanium alloy (a-Si1-xGex:H) properties and single junction solar cell performance have been studied. The hydrogenated amorphous silicon germanium films were deposited from the mixture of SiH4,GeH4 , and H2 dilution by the plasma enhanced chemical vapor deposition (PECVD) system at 27.12 MHz. It has been found that hydrogen dilution plays an important role in the properties of films. Adequate hydrogen dilution ratio can improve the photo conductivity and photosensitivity, but the higher or lower hydrogen dilution ratio both deteriorates the film properties. Power density influences on the deposition rate and electronic properties. Photo conductivity is higher for films deposited at higher power density for all hydrogen dilution ratios. Dark conductivity is almost the same for films deposited at two different power densities for all hydrogen dilution ratios. Germane to silane ratio (Xg) plays a leading role in single junction solar cell performance. Increasing gas phase ratio of germane (Xg) can raise the short circuit current (Jsc), but the higher Xg value will reduce the fill factor (F.F.) from 60.6 % to 48.71 % and deteriorate the cell efficiency from 6.326 % to 4.85 %. From the result of the quantum efficiency spectra, the spectral sensitivity of solar cell extends systematically towards longer wavelengths as increasing the Xg value in i layer from 8.3% to 16.7 %. To compare the amorphous silicon solar cell, when Xg values are at 8.3 % and 16.7 %, the Q.E. also decrease in the short wavelength region.