高吸光率三维电极-n-p结量子点太阳电池的制备及研究

Solar cells based on solution-processed semiconductor nanoparticles - colloidal quantum dots(CQDs) － have received much attention because of their high theoretical efficiency reaching 42% and low production cost. At present, the efficiency of CQD solar cells is not satisfying mainly due to the following three factors: (i) Organic ligands used to passivate the surface of the semiconductor nanoparticles produce insulating barriers between CQDs that militate against efficient carrier transport when processed into films; (ii) Limited by the exciton diffusion lengthes, the thickness of the cell can't reach micron level which results in the low solar absorption; (iii) Charge carriers photogenerated in the quasi-neutral region of the cell fail to reach the edge of the depletion region before they recombine. Here we establish an atomic ligand strategy that makes use of monovalent anions to enhance electronic transport and passivate surface. The three dimension transparent nanowires materials with high conduction are synthesized to use as electrodes for collecting photogenerated electrons. This three dimension electrode-n-p heterojunction structure makes sure photogenerated electrons can be collected efficiently while increasing the cell thickness. A quantum funnel constructed with different size quantum dots films is introduced in CQD solar cell, which induces an additional driving force for electrons diffusing from their point of generation toward an intended electron acceptor.

量子点太阳电池理论效率高达42%，并且具有制备原料丰富、制作简单、成本低廉的优点，是近年最受关注的薄膜太阳电池之一。量子点太阳电池目前效率不高，其主要的问题在于制备量子点过程中在颗粒表面起钝化作用的有机分子链较长，影响了光生电子的传输。同时，光生电子扩散长度的限制使得电池的厚度不能达到微米级，吸光层的厚度低导致太阳光的吸收利用率不高。光生电子的定向传输性也是影响电子收集的重要因素。针对这些问题，本课题研究采用单原子层包裹量子点的方法提高量子点中电子的迁移率，并且研究制备具高透光性，高导电性的纳米线材料作为电池的电极，形成三维电极-n-p结的体异质结构，保证在提高电池厚度的同时电子能得到有效的收集。设计电池结构，利用粒径不同的量子点材料，制备具有"量子漏斗"效应的电池，加强电子的定向传输性，提高电子的收集效率，从而提高电池的光电转换效率。

量子点太阳电池具有理论效率高，制备原料丰富、制作简单、成本低廉的优点，是非常受国内外关注的薄膜太阳电池。现今对这一类型电池的研究主要集中在量子点的可控合成和新材料的开发上，本项目同时在这两方面开展了一些相关的工作。首先，我们采用新的两相反应体系合成了硫化铅（PbS）和硫化镉量子点，其中PbS量子点是首次通过两相法制备成功。通过调控合成条件实现了量子点的粒径可调，从而实现了其光学性能可控。获得了合成条件对材料物性的影响规律，分析了两相反应的动力学机理过程。其次，对PbS量子点的表面进行了改性，成功采用小分子链接剂PbI3-和PbBr3-取代了合成过程中使用的长链有机分子油酸和油胺，加强了颗粒间的电子传输，提高了材料的光电性能。最后，首次成功制备了无衬底的PbS/CH3NH3PbI3的核壳纳米颗粒。这一核壳结构解决了单一PbS量子点在可见光区吸光性能不好，而CH3NH3PbI3不能利用红外光的问题，同时构建了台阶型的能带，提高了电池的光电性能，相较单独使用PbS的电池的效率提高了580%，比单独使用MAPI的电池效率也提高了71%。这部分研究也为制备核壳纳米材料提供了一种新的思路。