中间带有机金属卤化物钙钛矿单晶薄膜的化学溶液外延研究

In order to improve the conversion efficiency of organic metal halide perovskite (MAPbX3) thin film solar cell further, high-quality crystalline thin film and long wavelength absorption extension are two promising routes which people must follow. Formation of intermediate band in the band gap of the absorption layer is an effective way to extend the utilizing spectrum wavelength range of solar cells, to the long wavelength side. For the similar reason and its outstanding photoelectric properties, the research and application of optoelectronic devices based on this kind of material needs single crystalline thin film as well. Therefore, in this project it is proposed that the single crystalline thin film MAPbX3 would be grown using an innovative low-cost chemical solution epitaxy (CSE) method. The CSE apparatus is designed elaborately with controllable temperature, dynamically adjustable solution composition, stirring fluid and rotatable substrate. Thin film growth thermodynamics, kinetics and chemical reaction equilibrium theories would be applied to calculate the growth parameters like nucleus density, nucleation rate, nucleus critical radius, critical conditions for 2D and 3D growth and so on. These means aim at clarifying the nucleation mechanism and growth mode control principles and strategies of MAPbX3 CSE. The intermediate band MAPbX3 thin films would be synthesized by doping the solution by ions of impurity elements such as Hg. This research would facilitate new breakthrough of MAPbX3 thin film solar cell performance, and the success of the single crystalline MAPbX3 thin film growth would also clear one of the obstacles to the development and application of optoelectronic devices based on it.

为了进一步提高有机金属卤化物钙钛矿（MAPbX3）薄膜太阳电池效率，高质量晶体薄膜和长波吸收拓展是两个方向；在材料禁带中形成中间带是拓展长波吸收的有效手段；同时MAPbX3也是优异的光电材料，其光电器件的应用需要高品质单晶薄膜。因此，本项目创新性地采用低成本化学溶液外延法，研究新概念的中间带甲胺铅碘MAPbI3单晶薄膜的生长机理。采用自主设计可控温、溶液成分动态可调、可搅拌、衬底可旋转的溶液外延装置，结合薄膜生长热力学、动力学和化学反应平衡等理论，计算成核密度、成核速率、晶核临界半径、2D与3D生长临界条件等，旨在阐明单晶MAPbI3薄膜溶液外延的成核机制与生长模式调控原理与手段，获得高品质单晶薄膜。通过向溶液中掺Hg等杂质离子，制备具有杂质带的MAPbI3薄膜中间带材料。这将促进MAPbX3薄膜太阳电池的效率取得新的突破，其单晶薄膜的成功制备也将扫除MAPbI3光电器件应用的一大障碍。

以往其他材料体系的经验以及现有的研究证明，绝大多数情况下，同一材料的单晶形态的多数性能优于其多晶形态，卤铅钙钛矿光电材料亦是如此。用溶液法容易生长出其体单晶，然而应用于器件时需采用薄膜。另一方面，有机金属卤铅钙钛矿的带隙可调，是制备中间带光伏材料的理想基体材料，而中间带太阳电池有望以单结太阳电池的成本获得三结叠层太阳电池的光电转换效率。基于以上动机，本项目集中研究了以CH3NH3PbBr3为代表的有机金属卤铅钙钛矿单晶薄膜、及其Bi掺杂的CH3NH3PbBr3:Bi杂质中间带单晶薄膜的溶液法外延生长，经过在玻璃、FTO、单晶硅、CdTe等多种衬底上进行等离子体处理等多种工艺尝试，初步实现了上述两种材料的体单晶和单晶薄膜的溶液法生长，单块单晶薄膜尺寸达到1mm*1mm*6.3um，体单晶尺寸达6mm*5mm*2mm，并用旋涂法制备和研究了掺Bi多晶杂质中间带太阳电池器件。通过多种光学方法证明，掺Bi后基体材料的带隙不变，吸收光谱红外方向拓展，间接证明有效形成了Bi的杂质中间带。初步阐明了上述材料的溶液法外延生长与调控机理，为后续在各种异质衬底上进行无图形掩模直接生长上述高品质单晶薄膜材料及其大规模器件应用打下了基础，探明了道路。