新型柔性石墨烯/超薄硅异质结太阳能电池构建及其增效机理研究

Flexible Graphene/ultra-thin silicon Schottky solar cell has trigged off much attention due to its easy accessible raw materials, simple preparation process, bendable, light and extensive application fields. However, as a great potential and novel solar cell, how to improve it’s light absorption of silicon substrate and enhance the power conversion efficiency should be solved urgently. This project presents a low-cost nano-copper particle catalyzed etching technology for texturing ultra-thin silicon with large scale inverted pyramid arrays, which is expected to balance between the optical absorption enhancement and surface recombination suppression. Additionally, the carbon quantum dot (CQD) layer, as passivation layer and electron blocking layer was firstly brought into the interface of ultra-thin silicon and graphene. Our work aims to fabricate the high efficiency flexible graphene/ultra-thin silicon solar cell solar cell by combining the suitable inverted pyramid arrays and masterly introduction of CQD layer. The efficiency enhancement mechanism of the device is discussed and essentially revealed through studying the effect of CQD layer introduction on the Schottky barrier and building the band diagrams of doped graphene, CQD and silicon substrate. The development of present project is beneficial to solve the bottlenecks of efficiency enhancement of novel flexible graphene/ultra-thin silicon solar cell, which would establish the theoretical and practical basis for promoting the advancement of novel solar cell technology.

柔性石墨烯/硅肖特基结太阳能电池因其原材料丰富、制备工艺简单且具有柔性、质轻、适用范围广等优势而备受关注，然而作为一种极具潜力的新型电池，如何改善其陷光能力、提高器件转换效率是其目前亟待解决的关键问题。本项目提出采用低成本纳米铜催化化学刻蚀技术在超薄硅基底表面制备大规模倒金字塔阵列结构，以实现增加光谱吸收及降低载流子表面复合之平衡。其次，创新性地将碳量子点引入至石墨烯/超薄硅界面处作为减反钝化介质和电子阻挡层，通过合理的纳米织化处理结合碳量子点的巧妙使用，最终实现高效柔性硅基太阳能电池的制备。通过探明碳量子点引入对石墨烯/硅界面势垒的影响规律，建立掺杂石墨烯、碳量子点以及硅基底之间的能带结构关系，从本质揭示新型电池结构的提效机理。该项目的实施将有助于解决目前新型柔性石墨烯/硅太阳能效率提升所面临的瓶颈问题，为推动新型太阳能电池技术的进步奠定理论及实践基础。

针对传统硅基太阳能电池存在硅用量大、制备工艺复杂、设备成本高等问题，本项目提出柔性超薄硅与石墨烯材料相结合制备柔性异质结太阳能电池的思路。通常超薄平面硅基对光吸收率较低，本项目通过Cu(NO3)2-H2O2-HF金属铜辅助刻蚀代替传统KOH碱性刻蚀，能够硅基减薄的同时实现制绒处理；相较于KOH碱性刻蚀，Cu(NO3)2-H2O2-HF刻蚀大大缩短了减薄时间，节约了成本，减薄速率是KOH碱刻蚀速率的12.2倍。倒金字塔纳米织化处理提升了对光线的吸收率，对光的反射率达到10%以下。本项目采用等离子增强气相沉积（PECVD）制备了石墨烯薄膜材料，以少层石墨烯取代传统单层石墨烯构建了Gr/Si器件，提高了石墨烯的功函数和导电性，器件性能得到提升；采用电化学插层剥离二硫化钼（MoS2）晶体和二硫化钨（WS2）纳米片，并将其引入到Gr-Si界面作为空穴传输层。提高器件肖特基势垒高度阻拦电子，加快了空穴的隧穿，避免严重的界面复合，器件的开路电压（VOC）得到较大提升，JSC也有所增加，经过硝酸掺杂以后，Gr/MoS2/Si和Gr/WS2/Si器件转换效率分别达到7.95%和9.82%。.采用化学法制备了用量子点（QDs）并将其作为中间层修饰Gr-Si界面，由于独特的能带结构和电荷传输特性，碳量子点（CQDs）在Gr/CQDs/Si太阳电池中起到了电子阻挡和空穴传输的双重作用，降低了太阳电池的J0，同时增大了VOC，从而器件的整体性能得到了提升。调节CQDs薄膜的厚度以及CQDs的尺寸，并旋涂TiO2减反涂层后，太阳电池TiO2/Gr/CQDs/Si最终在AM 1.5g辐照下获得了9.97%的光电转换效率。提出引入氧化石墨烯量子点（GOQD）作为界面修饰材料，通过控制GOQD粒子大小、厚度研究其对Gr/Si太阳能电池性能的影响，在最佳厚度(26 nm)和颗粒尺寸(4.15 nm)条件下，硝酸掺杂处理实现了Gr/GOQDs/Si太阳能电池转换效率为13.67%，且表现出不错的稳定性。