Radiative Efficiency Limit with Band Tailing Exceeds 30% for Quantum Dot Solar Cells
Radiative Efficiency Limit with Band Tailing Exceeds 30% for Quantum Dot Solar Cells
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DOI：
10.1021/acsenergylett.7b00923
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发表时间：
2017-11-01
影响因子：
22
通讯作者：
Bulovic, Vladimir
中科院分区：
文献类型：
--
作者：
Jean, Joel;Mahony, Thomas S.;Bulovic, Vladimir
胶体量子点（QD）薄膜尽管具有无序的性质，但却是很有前途的太阳能光伏（PV）吸收剂。无序PV材料面临低于理想Shockley-Queisser界限的功率转换效率极限，因为通过带尾态的辐射复合增加。然而，量子点太阳能电池中能带拖尾的研究在很大程度上限于间接测量，使其最终效率受到质疑。在这里，我们使用光热偏转光谱（PDS）的鲁棒性的特征的硫化铅（PbS）量子点薄膜的吸收边不同的带隙，配体，和领先的设备中使用的处理条件。我们还全面概述了许多商业和新兴光伏技术中的能带拖尾，包括c-Si，GaAs，a-Si：H，CdTe，CIGS和钙钛矿，然后计算每种技术结合Urbach能带拖尾的详细平衡效率限制。我们的PDS测量PbS量子点显示出尖锐的指数带尾，与Urbach能量为22 +/- 1 meV的碘化物处理的膜和24 +/- 1 meV的乙硫醇处理的膜，相当于多晶CdTe和CIGS膜。根据这些结果，我们计算出最大效率为31%，接近于没有带尾的理想极限。这一发现表明，无序并不限制量子点太阳能电池的长期潜力。
Thin films of colloidal quantum dots (QDs) are promising solar photovoltaic (PV) absorbers in spite of their disordered nature. Disordered PV materials face a power conversion efficiency limit lower than the ideal Shockley-Queisser bound because of increased radiative recombination through band tail states. However, investigations of band tailing in QD solar cells have been largely restricted to indirect measurements, leaving their ultimate efficiency in question. Here we use photothermal deflection spectroscopy (PDS) to robustly characterize the absorption edge of lead sulfide (PbS) QD films for different bandgaps, ligands, and processing conditions used in leading devices. We also present a comprehensive overview of band tailing in many commercial and emerging PV technologies including c-Si, GaAs, a-Si:H, CdTe, CIGS, and perovskites then calculate detailed-balance efficiency limits incorporating Urbach band tailing for each technology. Our PDS measurements on PbS QDs show sharp exponential band tails, with Urbach energies of 22 +/- 1 meV for iodide-treated films and 24 +/- 1 meV for ethanedithiol-treated films, comparable to those of polycrystalline CdTe and CIGS films. From these results, we calculate a maximum efficiency of 31%, close to the ideal limit without band tailing. This finding suggests that disorder does not constrain the long-term potential of QD solar cells.