Light-trapping enhanced thin-film III-V quantum dot solar cells fabricated by epitaxial lift-off
Light-trapping enhanced thin-film III-V quantum dot solar cells fabricated by epitaxial lift-off
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DOI：
10.1016/j.solmat.2017.12.014
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发表时间：
2018-07-01
影响因子：
6.9
通讯作者：
Guina, M.
中科院分区：
文献类型：
--
作者：
Cappelluti, F.;Kim, D.;Guina, M.
报道了一种采用外延剥离(ELO)技术制备的n-i-p(+)深结平面背反射层的InAs/GaAsQD太阳电池。外部量子效率测量表明，与基于晶片的量子点电池相比，ELO量子点电池中的量子点光电流增加了两倍。在GaAs波长范围内，ELO量子点电池完美地保持了基线单结ELO电池的集流效率。我们通过全波光学模拟证明，在ELO池的后部集成一个微图案化的衍射栅可以使量子点对近红外光的捕获能力提高十倍以上。通过基于物理的模拟对实验结果进行了深入的讨论，以找出量子点动力学和缺陷对电池光伏行为的影响。研究表明，量子点堆中的非辐射复合是影响器件开路电压的瓶颈。更重要的是，我们的理论计算表明，Tanabe等人2012年从高质量III-V量子点太阳能电池的实验数据中确定的0.3V的V-OC偏移量是测量可获得的V-OC的可靠指标，并通过减少非辐射复合来量化改进的范围。在材料质量问题得到解决的前提下，通过传输和严格的电磁模拟，我们证明了具有20层InAs/GaAsQD层的光陷增强型薄膜电池在非聚光环境温度下的效率高于28%。如果能够充分利用光子回收，30%的效率被认为是可行的。
We report thin-film InAs/GaAs quantum dot (QD) solar cells with n - i - p(+) deep junction structure and planar back reflector fabricated by epitaxial lift-off (ELO) of full 3-in wafers. External quantum efficiency measurements demonstrate twofold enhancement of the QD photocurrent in the ELO QD cell compared to the wafer-based QD cell. In the GaAs wavelength range, the ELO QD cell perfectly preserves the current collection efficiency of the baseline single junction ELO cell. We demonstrate by full-wave optical simulations that integrating a micro patterned diffraction grating in the ELO cell rearside provides more than tenfold enhancement of the near infrared light harvesting by QDs. Experimental results are thoroughly discussed with the help of physics-based simulations to single out the impact of QD dynamics and defects on the cell photovoltaic behavior. It is demonstrated that non radiative recombination in the QD stack is the bottleneck for the open circuit voltage (V-OC) of the reported devices. More important, our theoretical calculations demonstrate that the V-OC offset of 0.3 V from the QD ground state identified by Tanabe et al., 2012, from a collection of experimental data of high quality III-V QD solar cells is a reliable - albeit conservative - metric to gauge the attainable V-OC and to quantify the scope for improvement by reducing non radiative recombination. Provided that material quality issues are solved, we demonstrate - by transport and rigorous electromagnetic simulations - that light-trapping enhanced thin-film cells with twenty InAs/GaAs QD layers reach efficiency higher than 28% under unconcentrated light, ambient temperature. If photon recycling can be fully exploited, 30% efficiency is deemed to be feasible.