以旋轉塗布磷摻雜源製程應用於超高密度矽量子點薄膜之研究

Abstract

奈米結晶矽量子點近年來廣泛運用在光伏電池上，其能隙可調變性被視為可行的方法來突破單一能隙最高理論效率值。為提升量子點密度或縮短量子點間距以提升載子穿隧機率，我們在之前研究中已提出並成功開發漸變矽過多氧化矽多層膜(Gradient Si-rich oxide multi-layer, GSRO-ML)結構製作出超高密度矽量子點薄膜。為了近一步提升薄膜電性，藉由雜質(硼或磷)摻雜及活化提升電流密度以及導電性是此研究的主要目的。在2014年以POCl3熱擴散方式使磷原子摻雜於GSRO-ML結構中，薄膜光電特性有明顯提升，但填充因子的下降使效率被限制。 此篇論文著重於改變摻雜方式，利用旋轉塗布磷摻雜源P2O5進行預沉積後，進行熱擴散活化磷原子於GSRO-ML結構中，並探討磷摻雜效應及缺陷修補，使光電特性提升之外，也能有效提高填充因子。在磷摻雜效應下，GSRO-ML結構能保有摻雜前的結晶率及高吸收係數，隨著摻雜量的增加光伏特性有明顯提升且達到最佳摻雜程度，而在更高濃度下由於過多的磷原子聚集於量子點和二氧化矽交界處，載子遷移率大幅降低使整體效益下降。在最佳摻雜量的條件下，改變高溫熱擴散的活化時間及溫度，對磷原子驅入所需活化條件做分析，進一步分析更有效的活化參數，使光伏電池達到最佳效率值。除此之外，改變GSRO-ML結構周期數可發現，當結構週期和磷原子摻雜量增加時，光伏電池光電特性明顯提升，具有極大潛力達到更高效率值，更能在未來達到多重能隙疊層電池以突破單一能隙電池效率極限。總結之，此研究驗證了磷摻雜效應於量子點薄膜中對光伏電池效率提升顯著，填充因子大幅改善之外，並具有極大淺力達成多重能隙疊層電池。

Recently, nanocrystalline silicon quantum dot (nc-Si QD) thin films are widely used in the solar cells (SCs). The high-tunable ability of energy bandgap (Eg) is regarded as a feasible method to break through the highest theoretical conversion efficiency of the single Eg. In order to increase the QD density or reduce the separation between QD for enhancement of carrier tunneling probability, the super-high Si QD thin films gradient Si-rich oxide multi-layer (GSRO-ML) has been demonstrated in our previous work. To further enhance the film electrical properties, the main purpose is increasing the current density and conductivity by impurity (B or P atoms) doping and activation. In 2014, the POCl3 process of thermal diffusion was carried out for P atoms doped in GSRO-ML structure. The photoelectric properties have significantly improved but the decline in fill factor (F.F.) limits the PV’s conversion efficiency. The main propose of this study focuses on changing the doping method. The “pre-deposition” is carried out by spin-on process that using the phosphor-doped P2O5. After spin-on, P atoms are activated into the GSRO-ML structure in thermal diffusion furnace. With P atom doping, optoelectronic properties are clearly enhanced but also the defeats repaired that the fill factor is effectively increased. Under P-doping, the crystallinity and high absorption coefficient are well-maintained. The electrical and PV properties are enhanced and lead to the optimized performances with increasing P2O5 dopant concentration. At higher concentrations, surplus P atoms accumulate between the interface of Si QD and SiO2 matrix that carrier mobility significantly reduced and results in poorer conversion efficiency. Under the optimized doping conditions, changing the diffusion temperature and time to find out more effective activation parameters and achieve the best conversion efficiency in this study. In addition, when the thickness of GSRO-ML structure and the doping amount of P atoms increase, the photoelectric properties of cells are obviously improved which has a great potential to achieve higher conversion efficiency. The improvement plays an important role for achieving multi-bandgap tandem solar cell to break through the single-bandgap cell’s theoretically conversion efficiency in foreseeable future. In summary, this study demonstrates the P-doping effect on GSRO-ML Si QD thin films structure and the PV’s performances are greatly improved. The structure is potential and available to achieve high-efficiency solar cell in high-technology industry.