关联性硅基多界面卤素钙钛矿集成光伏器件的制备与量子输运性能的研究

The core thought of this project is to form a tandem system of photovoltaic devices on a n-type silicon wafer with two-terminal output, by using Si-based SIS and hybrid caesium formamidinium lead halide perovskite solar cells we obtained previously. The purpose is to simplify the overall structure of the tandem device and promote the photoelectric conversion and stability, and reduce the defect density in the bulk and at the interface as well. Several oxide film materials with different functions will be coupled to passivation, tunneling and carriers transfer layers of the tandem system, so as to lessen the light reflection and parasitic absorption. The spectral and current matching will be achieved for top and below devices, owing to the equilibrium of "quantum tunneling" and "surface passivation", the compatibility of "space charge region" and "inversion layer", and the amalgamation of "top" and "below" being formed. Together with density function theory (DFT) and molecular dynamics (MD) calculation, the effective experimental techniques for film deposition and characterization with physical or chemical analysis methods will be used in our investigation into the exploration of structural and electronic defects within bulk and interfaces of the films, as well as the mechanism of photo-generated carriers recombination. It is important to reveal the rule of quantum transport and optimize photoelectric conversion performance of the tandem device, which is focused on the exploration of advanced PV materials and development of new PV devices system.

本项目的核心思路，是利用我们已经获得的硅-基SIS结构与卤素杂化钙钛矿光伏器件的分立单元，在n-型单晶硅片上形成两端点功率输出的级联系统，目的是简化这一级联器件的整体结构，并提高光电转换功能、系统的稳定性和降低材料体内与界面上的缺陷密度。将几种不同功能的氧化物薄膜材料耦合到器件系统的界面钝化层、量子隧穿层、空穴和电子的传输层，减少光反射和寄生吸收，实现两个器件单元之间的光谱与电流匹配，从而达到“量子隧穿”和“表面钝化”相平衡、“空间电荷区”与“反型层”相兼容、“上光伏”与“下光伏”相融合的光电结构。采用有效的物理-化学沉积技术和薄膜微结构-性能表征实验，结合密度泛函与分子动力学理论计算的研究方法，将探知薄膜体内或界面上的结构缺陷、电子态分布和光生载流子复合模式作为研究的重点，揭示该级联器件的量子输运规律和优化光电转换性能，对于探索先进光伏材料的应用和开拓新型光伏器件系统具有重要的意义。

利用能带工程和半导体材料的光电转换性质，将金属卤素钙钛矿薄膜太阳电池（简称为PSCs）与n-型单晶硅基太阳电池叠加为两端级联结构，实现对单结Shockley-Queisser效率极限（33%）的突破，对推动低成本、简单、高效的太阳电池技术的发展，具有重要的科学和工程意义。本项目在研究中，取得了以下结果：（1）以SQIS或M-SQIS结构为核心，调控优化了ITO/a-SiOx(M=In, Mo)复合薄膜的梯度电子结构，形成p-型/本征导电的界面混合过渡层，具有钝化-反型和空穴传输特征；由密度泛函（DFT）计算给出负铟（In-）离子提供了扩展态Ev+0.3eV，非晶结构缺陷导致大量的局域态，使空穴的输运为隧穿加针孔。同样，Mo掺杂在a-SiOx带隙中也引入了若干量子态，分别位于价带顶Ev+3.67eV，3.69 eV，4.93eV，5.08eV和5.39eV的位置。以SiOx/TiNy(y<1)复合薄膜在背面起电子抽取作用，缺氮产生了TiNy中的空位，在n-Si/SiOx-TiNy界面区，存在0.23eV的价带差，光生电子隧穿加针孔通过SiOx后被TiNy收集，同时，在界面处形成了阻挡空穴的肖特基势垒和价带偏移（ΔEv=2.28eV）。从而达到“量子双隧穿”和“表面钝化”相平衡、“空间电荷区”与“反型层”相兼容的能带结构。实验光电转换效率由12.2%提高到16.7%，通过模型计算的效率达到22.1%。（2）在大气环境下，于0.1cm2 面积上制备经MAPyA原位处理的稳定黑相CsPbI2Br薄膜（PA）,非辐射复合和电荷传输实验确认了它的光伏相稳定性。对于CsPbI3基的PSCs器件进行测试，在FF和VOC显著增强的情况下，器件的最高效率超过16.0%，经历120天仍保持了97.0%的初始效率。而α相CsPbI2Br(1%CaCl2& 2%InCl3)薄膜的致密性、相稳定性和少子寿命的提高，使得PCE从9.6%增加到14.1%。（3）首次通过深度剖析XPS探测到TOPCon器件中多晶硅薄膜内存在P-O键及衍生物，利用热力学函数（焓、熵、吉布斯能、形成能）确认其存在的必然性。对于PSCs/(SQIS或M-SQIS或M-TOPCon) 级联光伏器件，半经验方法预测的光电转换效率在31-38%区间，而实验研究值与当前的世界纪录（32.5%）还有较大的差距。