Mahmood Khalid, Swain Bhabani Sankar, Jung Hyun Suk
School of Advanced Materials Science & Engineering, Sungkyunkwan University, Suwon 440-746, Republic of Korea.
Nanoscale. 2014 Aug 7;6(15):9127-38. doi: 10.1039/c4nr02065k.
In this paper, ZnO and Al-doped ZnO films were deposited using the electrospraying method and studied for the first time as photoanodes for efficient perovskite solar cells. Effects of substrate temperature, deposition time, applied voltage, substrate-to-nozzle distance and flow rate (droplet size) on the morphology of ZnO were studied with the help of FE-SEM images. The major factors such as the droplet size of the spray, substrate temperature and substrate-to-nozzle distance at deposition control the film morphology. Indeed, these factors determine the density of the film, its smoothness and the flow of solution over the substrate. The droplet size was controlled by the flow rate of the spray. The substrate-to-nozzle distance and flow rate will both regulate the solution amount deposited on the surface of the substrate. The most favorable conditions for a good quality ZnO thin film were a long substrate-to-nozzle distance and lower solution flow rates. In situ droplet size measurement shows that the size and dispersion of particles were narrowed. The method was shown to have a high deposition rate and efficiency relative to well-established thin film deposition techniques such as chemical and physical vapor deposition. In addition, it also allows easy control of the microstructure and stoichiometry of the deposits. The pure ZnO film produced under optimum conditions (440 nm thick) demonstrated a high power conversion efficiency (PCE) of 10.8% when used as a photoanode for perovskite solar cells, owing to its high porosity, uniform morphology and efficient electron transport. For thicker films a drastic decrease in PCE was observed due to their low porosity. We also observed that the open-circuit voltage increases from 1010 mV to 1045 mV and also the PCE increases from 10.8% to 12.0% when pure ZnO films were doped with aluminum (Al). Under atmospheric pressure, the electrospraying system produces the reasonably uniform-sized droplets of smaller size, so the films have a smooth surface and are highly suited for optoelectronic applications.
在本文中，采用电喷雾法沉积了氧化锌（ZnO）和铝掺杂氧化锌（Al - doped ZnO）薄膜，并首次将其作为高效钙钛矿太阳能电池的光阳极进行研究。借助场发射扫描电子显微镜（FE - SEM）图像，研究了衬底温度、沉积时间、施加电压、衬底与喷嘴距离以及流速（液滴尺寸）对ZnO形貌的影响。沉积时喷雾的液滴尺寸、衬底温度和衬底与喷嘴距离等主要因素控制着薄膜的形貌。实际上，这些因素决定了薄膜的密度、光滑度以及溶液在衬底上的流动情况。液滴尺寸由喷雾流速控制。衬底与喷嘴距离和流速都会调节沉积在衬底表面的溶液量。高质量ZnO薄膜的最有利条件是衬底与喷嘴距离长且溶液流速较低。原位液滴尺寸测量表明颗粒的尺寸和分散性变窄。相对于化学气相沉积和物理气相沉积等成熟的薄膜沉积技术，该方法显示出高沉积速率和效率。此外，它还便于控制沉积物的微观结构和化学计量比。在最佳条件下制备的纯ZnO薄膜（厚度为440 nm）用作钙钛矿太阳能电池的光阳极时，由于其高孔隙率、均匀的形貌和高效的电子传输，展现出10.8%的高功率转换效率（PCE）。对于较厚的薄膜，由于其低孔隙率，观察到PCE急剧下降。我们还观察到，当纯ZnO薄膜掺杂铝（Al）时，开路电压从1010 mV增加到1045 mV，PCE也从10.8%增加到12.0%。在大气压下，电喷雾系统产生尺寸合理均匀且较小的液滴，因此薄膜具有光滑的表面，非常适合用于光电子应用。
