研究人员开发提升转换效率80%的3D纳米锥基太阳能电池

由橡树岭国家实验室(Oak Ridge National Laboratory)的Jun Xu带领的研究小组已经开发出以3D纳米锥基太阳能电池平台，声称可以改善电荷传输机制从而提高太阳能电池光电转换效率约达80%。

该技术克服了太阳光子所产生的电荷传输不良问题。这些电荷——包括带负电的电子和带正电的空穴——通常成为体材料及其界面中的缺陷，并因此降低了性能。

“为了解决降低太阳能电池效率的电荷捕获问题，我们制造了一种纳米锥基太阳能电池并发明了方法来合成这些电池，事实证明改善了电荷的收集效率。”Xu说。他是橡树岭国家实验室化学科学部的成员之一。

这种新的太阳能结构包括由P型半导体环绕的N型纳米锥。N型纳米锥由氧化锌构成，并作为整个结构的导电结（junction）和电子导体。P区由多晶碲化镉构成并作为主要的光吸收介质和空穴导体。

使用该实验室层次的方法，Xu和他的同事可以获得3.2%的光电转换效率，相比之下使用相同材料的传统平面结构转换效率只有1.8%。

“我们设计的3D结构可以提供一个内建电场区，以此来提高电荷传输的效率，使太阳光转换成电能变得更高效。”Xu说。

这种太阳能材料的主要特点包括其独特的电场分布，这一特点实现了高效的电荷传输；利用低成本专用方法合成的纳米锥，以及减少了半导体中的缺陷和空位。后者增强了太阳光子转换为电能这一光电性能。

由于高效的电荷传输机制，这种新的太阳能电池可以接受有缺陷的半导体材料并减少下一代太阳能电池的制造成本。

“支持我们发明的重要思想就是纳米锥结构在结（junction）尖端产生一个强电场区域，可以有效地分离、注入和收集少数载流子，从而比使用相同材料传统平面结构电池更高效。”Xu说。

这一技术的理论研究已经得到了今年IEEE光伏专家会议的认可，并将在IEEE学报上发表。论文标题为“纳米锥尖端薄膜太阳能电池中的高效电荷传输”以及“基于氧化锌纳米锥上生长的多晶碲化镉薄膜纳米结太阳能电池”。

为这项技术做出贡献的还有Sang Hyun Lee, X-G Zhang, Chad Parish, Barton Smith, Yongning He, Chad Duty和Ho Nyung Lee。

纳米锥基太阳能电池包括N型纳米锥，P型区、透明导电氧化物（TCO）和玻璃衬底。

编译：Aileen Zhu

点击参考原文：Nanocone-based solar cell improves charge transport

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Nanocone-based solar cell improves charge transport

A team led by Oak Ridge National Laboratory's Jun Xu has developed a 3D nanocone-based solar cell platform that claims to improve charge transport thereby boosting the light-to-power conversion efficiency of photovoltaics by nearly 80 percent.

The technology overcomes the problem of poor transport of charges generated by solar photons. These charges—negative electrons and positive holes—typically become trapped by defects in bulk materials and their interfaces and degrade performance.

"To solve the entrapment problems that reduce solar cell efficiency, we created a nanocone-based solar cell, invented methods to synthesise these cells and demonstrated improved charge collection efficiency," said Xu, a member of ORNL's Chemical Sciences Division.

The new solar structure consists of n-type nanocones surrounded by a p-type semiconductor. The n-type nanoncones are made of zinc oxide and serve as the junction framework and the electron conductor. The p-type matrix is made of polycrystalline cadmium telluride and serves as the primary photon absorber medium and hole conductor.

With this approach at the laboratory scale, Xu and colleagues were able to obtain a light-to-power conversion efficiency of 3.2 per cent compared to 1.8 per cent efficiency of conventional planar structure of the same materials.

"We designed the three-dimensional structure to provide an intrinsic electric field distribution that promotes efficient charge transport and high efficiency in converting energy from sunlight into electricity," Xu said.

Key features of the solar material include its unique electric field distribution that achieves efficient charge transport; the synthesis of nanocones using inexpensive proprietary methods; and the reduction of defects and voids in semiconductors. The latter provides enhanced electric and optical properties for conversion of solar photons to electricity.

Because of efficient charge transport, the new solar cell can tolerate defective materials and reduce cost in fabricating next-generation solar cells.

"The important concept behind our invention is that the nanocone shape generates a high electric field in the vicinity of the tip junction, effectively separating, injecting and collecting minority carriers, resulting in a higher efficiency than that of a conventional planar cell made with the same materials," said Xu.

Research that forms the foundation of this technology was accepted by this year's Institute of Electrical and Electronics Engineers photovoltaic specialist conference and will be published in the IEEE Proceedings. The papers are titled 'Efficient Charge Transport in Nanocone Tip-Film Solar Cells' and "Nanojunction solar cells based on polycrystalline CdTe films grown on ZnO nanocones.'

The research was supported by the Laboratory Directed Research and Development programme and the Department of Energy's Office of Nonproliferation Research and Engineering.

Other contributors to this technology are Sang Hyun Lee, X-G Zhang, Chad Parish, Barton Smith, Yongning He, Chad Duty and Ho Nyung Lee. UT-Battelle manages ORNL for DOE's Office of Science.

Nanocone-based solar cell consisting of n-type nanocones, p-type matrix, transparent conductive oxide (TCO) and glass substrate.

编译：Aileen Zhu