高电荷收集效率的量子点敏化太阳能电池

Quantum dot - sensitized solar cells (QDSCs) promise a breakthrough in the solar to electric power conversion, far exceeding the theoretical S-Q limit in traditional solar cells, because quantum dots (QDs) are capable of multiple exciton generation, leading to a high theoretical power conversion efficiency (44%). However, the attained power conversion efficiency of today’s QDSCs is way below the theoretical limit, primarily attributable to the fact that lots of surface defects in quantum dots allows high charge recombination and low electron collection. Tremendous evidence published in literature including our research has indicated the removal and at least the minimization of surface defects and their detrimental impacts are the paramount challenge to advance the QDSCs research with much enhanced power conversion efficiency. We propose to in-situ deposit a thin conformal layer of Se or Se/CuxSe of a few angstroms coated on the surface of CdSe or CdSeTe quantum dots. Not only would such a conformal coating reduce and repair the surface defects of the quantum dots to suppress the charge recombination, but also establish a built-in bias electric field at the interface between the P-type coating and the N-type quantum dots to facilitate the charge separation, to promote the electron injection, and to accelerate the hole transfer away from the interface. It is anticipated that the charge collection efficiency of QDSCs will be significantly enhanced, consequently resulting in a much higher power conversion efficiency and paving the ways for the further advancement of QDSCs. To this end, our research would focus on the design and control of Se or Se/CuxSe layer with desired chemical composition, crystallinity, thickness, and conformal coverage to attain and to understand high charge collection efficiency, dynamic exciton separation, accelerated electron injection and rapid hole transfer at various interfaces. This research is anticipated to shed some light on the fundamental understanding of the influences of the phase composition, crystal- and nanostructures, surface and interface defects on the exciton generation and charge separation and transportation in QDSCs. This research would be beneficial to the development of the next generation solar cells.

依据量子点多重激子效应理论，量子点敏化太阳能电池（QDSC）可以突破半导体S-Q理论极限，具有更高的光电转换效率（44%）。然而，QDSC的转换效率远低于理论值，重要原因之一是其结构中存在大量界面缺陷，造成电子复合严重、电荷收集效率低。因此，减少界面缺陷或降低其负面作用是提高电池效率的重要途径。基于我们的前期工作，本项目提出在CdSe、CdSeTe等量子点表面原位形成具有空穴传输作用的Se或Se/CuxSe原子层。该修饰层不仅能减少和修复界面缺陷，抑制电子复合，还能在P型修饰层与N型量子点界面处形成内建电场，这将加快电子与空穴分离，促进电子注入和空穴转移，显著提高QDSC电荷收集效率。为此，本项目将重点研究：高电荷收集效率界面层的设计与调控；多界面下激子分离、电子注入、空穴转移等动力学过程；界面层相组成与结构对界面电荷传输的影响机制等。本研究将促进新一代太阳能电池技术的发展。

目前，QDSC的转换效率远低于理论值，重要原因之一是其结构中存在大量界面缺陷，造成电子复合严重、电荷收集效率低。为此，我们提出在量子点表面原位制备具有空穴传输作用的界面修饰层，修饰表面缺陷并促进空穴传输的研究思想，并展开研究。其中代表性的工作是采用连续离子层吸附与反应的方法在CdS/CdSe量子点的表面以及TiO2或ZnO与量子点的界面原位形成具有空穴传输作用的ZnSe与Se的复合界面材料，ZnSe可修饰表面缺陷，而Se作为p型半导体，可与n型量子点形成N-P异质结，从而促进空穴传输，从而提高了电荷分离、注入和收集效率。最终，基于TiO2的QDSC的光电转效率从3.4%提高至7.2%，而基于ZnO的光电转换效率也从3.3%提高至5.2%。这种界面修饰方法得到业内同行的高度认可。通过本项目研究，我们建立了具有高电荷收集效率 QDSC 的界面修饰层的制备与调控方法，从理论上阐明了多界面下激子分离、电子注入、空穴传输等动力学过程，以及界面缺陷对界面电荷收集效率的影响机制，丰富了光电转换相关理论，为新型太阳能电池光电转换效率的提升建立了一条有效途径。.在本项目支持下，发表学术论文13篇，均被SCI收录，其中影响因子超过10的6篇，影响因子5以上的11篇，这些论文被SCI引用444次。