Lateral photovoltaic effect in organic-inorganic hybrid films
When a beam of light hits the surface of Al-Alq3 film, largest lateral photovoltage (LPV) can be obtained in the upper layer and Si substrate, denoted as VAB and VCD respectively. The temperature dependence of LPV is shown in the upper inset.
When sufficiently energetic irradiation is incident on a p-n or MS/MOS junction, transverse photovoltaic effect can be observed, which is widely used in solar cells. Furthermore, when a nonuniform irradiation is applied on the junction, an additional photovoltage parallel to the plane of the junction can be obtained, which is called lateral photovoltaic effect (LPE). LPE has a wide range of applications, especially position-sensitive detectors (PSDs). Till now, the research on LPE is focused on the inorganic MOS/MS devices. However, obvious LPE on metal side can only be observed in the structures with nanoscale metal layer due to the shorting effect.
Recently, the research group, led by Prof. Gang Ni, from the Department of Optical Science and Engineering, Fudan University, has reported large lateral photovoltaic effect in the Al-Alq3 granular films on Si wafer, with a largest lateral photovoltage (LPV) sensitivity of 75mV/mm, which is close to the LPV value in inorganic LPE devices. Furthermore, optimal LPV can be achieved by adjusting the metal composition of granular film, which may be beneficial in the application of high sensitivity PSDs. With the decrease of temperature, the LPV increases accordingly, which is directly related to the temperature dependence of resistivity in the upper layer. Further theoretical fitting verified this point. It is reported in Chinese Optics Letters Vol. 12, No. 4, 2014 (/col/abstract.cfm?uri=col-12-4-040402).
Now, the study on microstructure is being carried out to understand the mechanism, and LPE devices with better performance are being developed for possible applications.
有机-无机复合颗粒膜的横向光伏效应
图片说明：当一束激光照射到Al/Alq3薄膜表面时，可在薄膜侧和衬底侧分别测得横向光伏电势差VAB和VCD，并随着照射位置的移动，可测得横向光伏效应（LPV）与位置的关系图；左上图所示为薄膜侧横向光伏电势差与温度的关系图。
横向光伏效应（LPE），是指当点光源照射到p-n结、MOS/MS等结构时，形成表面光生电势分布，由于其具有位置相关性，这一效应已被广泛用于位置传感器中。目前，横向光伏效应的研究主要集中在无机体系的MOS/MS结构中，且由于金属层的短路效应，通常只能在超薄金属层薄膜器件中才能明显观察到金属侧的横向光伏效应。
复旦大学光科学与工程系倪刚教授课题组将75 nm的Al-Alq3复合颗粒膜蒸镀到Si衬底上，观察到明显的横向光伏效应，其位置灵敏度最高可达75 mV/mm，这可以与无机体系相比拟。此外，通过调控其组分，可以获得优化的横向光伏效应。研究结果表明，随着温度的下降，横向光伏效应随之增强，这一增强与颗粒膜层电阻率的温度行为直接相关，进一步的理论拟合验证了这一点。相关研究成果发表在Chinese Optics Letters 2014年第4期上 (http://www.opticsinfobase.org/col/abstract.cfm?uri=col-12-4-040402)。
该研究创新性地将可调控薄膜电阻率的有机-无机复合颗粒膜引入传统的MOS结构中，从而可以获得优化横向光伏效应的位置敏感器件。目前，该研究正在探索新的材料体系，通过电阻率温度曲线的研究，寻找具有室温峰值的横向光伏效应器件。
图片说明：当一束激光照射到Al/Alq3薄膜表面时，可在薄膜侧和衬底侧分别测得横向光伏电势差VAB和VCD，并随着照射位置的移动，可测得横向光伏效应（LPV）与位置的关系图；左上图所示为薄膜侧横向光伏电势差与温度的关系图。