铁酸铋薄膜阴离子掺杂能带工程及光伏效应调控机理

In the past several years, bismuth ferric thin film has attracted research attention due to its anomalous photovoltaic effect, it shows smaller band gap than that of many other ferroelectrics, which results into large photo-voltage and high photo-current. However, bismuth ferric thin film was found to respond only to a very small window of the solar spectrum (blue and near ultraviolet). Because this part of the solar spectrum only accounts for very small amount of the incoming solar energy, the photovoltaic efficiencies of the thin films were limited by the small visible light absorption. In this work, a systematic study will be carried on to lower the band-gap energy of bismuth ferric thin film through one of the promising methods, such as anions doping, in order to improve the absorption of solar energy. It has been believed that the non-metallic atom doping with oxygen in the thin films is efficient to expand the absorption into the visible region and increase the concentration of the material of light generated carries, because its p states contribute to the band-gap narrowing by mixing with O 2p states. The focus of this project will be on the preparation process development of anions doped bismuth ferric thin films with different grain oriented growth, and reveal the optical and electrical properties such as absorption threshold of the doped films, open circuit voltage, short circuit voltage and resistivity etc. Furthermore, it is to explain the dependence of optical and electrical properties on some physical and material properties such as thickness, components, crystalline, and polarization of the thin films. The mechanism of p orbital hybridization and the photo-conductivity of the visible light induced polarization in doped bismuth ferric thin films are expected to be disclosed after the thorough investigation.

铁酸铋铁电薄膜的光伏效应近年来受到了研究者广泛的关注，这主要是由于铁酸铋具有反常光伏效应以及比其它铁电体更窄的带隙宽度，这些特点使其可以突破传统光伏材料开路电压无法超越禁带宽度的限制，并获得更大的短路电流。然而，研究发现铁酸铋的光吸收主要发生在蓝光区以及更短波段，获得的光子能量非常有限，从而限制了材料能量转换效率的进一步提高。本项目拟通过非金属阴离子掺杂的方式，利用非金属元素p轨道能级之间的杂化提高铁酸铋薄膜的光吸收阈值，扩大铁酸铋在可见光区的吸收范围，增加材料光生载流子的浓度，最终实现铁酸铋薄膜光-电转换效率的提高。重点研究不同晶粒生长取向的非金属阴离子掺杂铁酸铋薄膜的制备工艺，揭示掺杂薄膜的光吸收阈值、开路电压、短路电流、电阻率等光、电性能与薄膜厚度、组分、晶型、自发极化大小和方向之间的变化关系，阐明非金属元素p轨道能级杂化机理和掺杂铁酸铋薄膜的可见光激发极化导电机制。

铁酸铋(BiFeO3)铁电薄膜的光伏效应近年来受到了研究者广泛的关注，这主要是由于铁酸铋具有反常光伏效应以及比其它铁电体更窄的带隙宽度((2.2-2.8 eV)，这些特点使其可以突破传统光伏材料开路电压无法超越禁带宽度的限制，并获得更大的短路电流。然而，研究发现铁酸铋的光吸收主要发生在蓝光区以及更短波段，获得的光子能量非常有限，从而限制了材料能量转换效率的进一步提高。本项目通过溶胶-凝胶薄膜制备技术，利用不同衬底ITO/Si制备了阴离子掺杂铁酸铋薄膜。研究制备工艺对微观结构的影响，重点关注了掺杂薄膜的吸收截止边、开路电压、短路电流和电阻等光电性能的变化。通过液相沉积法制备铁酸铋和有机无机杂化材料CH3NH3PbI3复合多晶薄膜，制备了全钙钛矿型光电转换器件。与常规的BiFeO3多晶薄膜相比复合电极材料表现出较大的开路电压和光电转化性能。在可见光辐照下复合薄膜器件的开路电压Voc为1.62 V，短路电流密度为 1.74mA·cm-2，光电器件的转化效率约为1.5 %。利用第一性原理和二维相关分析技术定量地研究处理了阴离子掺杂铁酸铋钙钛矿材料的电子转移机制。研究卤素和C、N、P、S非金属离子修饰铁酸铋晶体的磁电性能影响机理。该项目成果将为新型铁电太阳能电池的进一步设计应用提供重要的科学依据。