Thiols Passivate Recombination Centers in Colloidal Quantum Dots Leading to Enhanced Photovoltaic Device Efficiency
Thiols Passivate Recombination Centers in Colloidal Quantum Dots Leading to Enhanced Photovoltaic Device Efficiency
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DOI：
10.1021/nn800471c
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发表时间：
2008-11-01
期刊：
影响因子：
17.1
通讯作者：
Sargent, Edward H.
中科院分区：
文献类型：
--
作者：
Barkhouse, D. Aaron R.;Pattantyus-Abraham, Andras G.;Sargent, Edward H.
最近有报道称，使用硫醇封端的配体可将胶体量子点 (CQD) 光伏 (PV) 器件的功率转换效率 (PCE) 提高 10 倍。我们在此发现，在代表性的胺封端的PbS胶体量子点材料系统中，硫醇处理后迁移率的改善仅导致PCE增加1.4倍。然后，我们继续研究硫醇处理后 PCE 中四倍增的剩余部分的起源。通过测量光致发光量子效率，我们发现暴露于硫醇中可以显着增强胶体量子点薄膜中的光致发光。相同的分子将开路电压 (V-oc) 从 0.28 V 增加到 0.43 V。综合起来，这些发现表明，作为复合中心（降低外部量子效率 (EQE)）和金属-半导体结界面态（降低 V-oc）的中间带隙态，使用硫醇基本上被钝化。通过接触硫醇，我们将 EQE 从 5% 提高到 22%，并结合 V-oc 的改进，将 1 μm 波长下 76 mW/cm(2) 下的功率转换效率提高到 2.6%。这些发现与光电导 PbS CQD 光电探测器的最新报告一致，即硫醇暴露基本上消除了深（0.3 eV）电子陷阱，仅留下浅（0.1 eV）电子陷阱。
The use of thiol-terminated ligands has recently been reported to enhance 10-fold the power conversion efficiency (PCE) of colloidal quantum dot (CQD) photovoltaic (PV) devices. We find herein that, in a representative amine-capped PbS colloidal quantum dot materials system, improved mobility following thiol treatment accounts for only a 1.4-fold increase in PCE. We then proceed to investigate the origins of the remainder of the quadrupling in PCE following thiol treatment. We find through measurements of photoluminescence quantum efficiency that exposure to thiols dramatically enhances photoluminescence in colloidal quantum dot films. The same molecules increase open-circuit voltage (V-oc) from 0.28 to 0.43 V. Combined, these findings suggest that mid-gap states, which serve as recombination centers (lowering external quantum efficiency (EQE)) and metal-semiconductor junction interface states (lowering V-oc), are substantially passivated using thiols. Through exposure to thiols, we improve EQE from 5 to 22% and, combined with the improvement in V-oc, improve power conversion efficiency to 2.6% under 76 mW/cm(2) at 1 mu m wavelength. These findings are consistent with recent reports in photoconductive PbS CQD photodetectors that thiol exposure substantially removes deep (0.3 eV) electron traps, leaving only shallow (0.1 eV) traps.