Chair of Chemistry of Polymeric Materials , University of Leoben , 8700 Leoben , Austria.
illwerke vkw Endowed Professorship for Energy Efficiency, Energy Research Center , Vorarlberg University of Applied Sciences , 6850 Dornbirn , Austria.
ACS Appl Mater Interfaces. 2018 Mar 28;10(12):10102-10114. doi: 10.1021/acsami.7b19442. Epub 2018 Mar 15.
After organic photovoltaic (OPV) cells achieved efficiency of more than 10%, the control of stability and degradation mechanisms of solar cells became a prominent task. The increase of device efficiency due to incorporation of a hole-transport layer (HTL) in bulk-heterojunction solar cells has been extensively reported. However, the most widely used HTL material, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), is frequently suspected to be the dominating source for device instability under environmental conditions. Thereby, effects like photooxidation and electrode corrosion are often reported to shorten device lifetime. However, often in environmental device studies, the source of degradation, whether being from the HTL, the active layer, or the metal cathode is rather difficult to distinguish because the external diffusion of oxygen and water affects all components. In this study, different HTLs, namely, those prepared from traditional PEDOT:PSS and also two types of molybdenum trioxide (MoO) are exposed to different environments, such as oxygen, light, or humidity, prior to device finalization under inert conditions. This allows investigating any effects within the HTL and from reactions at its interface to the indium tin oxide electrode or the active layer. The surface and bulk chemistry of the exposed HTL has been monitored and discussed in context to the observed device physics, dynamic charge transport, and spatial performance homogeneity of the corresponding OPV device. The results show that merely humidity exposure of the HTL leads to decreased device performance for PEDOT:PSS, but also for one type of the tested MoO. The losses are related to the amount of absorbed water in the HTL, inducing loss of active area in terms of interfacial contact. The device with PEDOT:PSS HTL after humid air exposure showed seriously decreased photocurrent by microdelamination of swelling/shrinkage of the hygroscopic layer. The colloidal MoO with water-based precursor solution presents slight decay of solar cell performance, also here caused by swelling/shrinking reaction, but by a combination of in-plane particle contact and resistance scaling with particle expansion. However, the device with quasi-continuous and alcohol-based MoO showed unharmed stable electrical performance.
在有机光伏（OPV）电池的效率超过 10%之后，控制太阳能电池的稳定性和降解机制成为一个突出的任务。在体异质结太阳能电池中加入空穴传输层（HTL）可以显著提高器件效率，这一点已经得到了广泛的报道。然而，最广泛使用的 HTL 材料聚（3,4-亚乙基二氧噻吩）：聚（苯乙烯磺酸盐）（PEDOT：PSS）经常被怀疑是在环境条件下导致器件不稳定的主要原因。因此，光电氧化和电极腐蚀等效应经常被报道会缩短器件的使用寿命。然而，在环境器件研究中，降解的来源，无论是来自 HTL、活性层还是金属阴极，通常都很难区分，因为外部氧气和水分的扩散会影响所有组件。在这项研究中，不同的 HTL，即由传统的 PEDOT：PSS 以及两种类型的三氧化钼（MoO）制备的 HTL，在惰性条件下最终制备器件之前，分别暴露于不同的环境中，如氧气、光照或湿度。这使得我们可以研究 HTL 内部以及其与氧化铟锡电极或活性层界面处的反应所产生的任何影响。暴露的 HTL 的表面和体化学性质已经在与观察到的器件物理、动态电荷传输以及相应 OPV 器件的空间性能均匀性相关的背景下进行了监测和讨论。结果表明，仅仅是 HTL 的湿度暴露就会导致 PEDOT：PSS 和一种测试的 MoO 的器件性能下降。这种损失与 HTL 中吸收的水分量有关，导致界面接触处的有效面积损失。在经过湿空气暴露后，PEDOT：PSS HTL 的器件显示出严重的光电流下降，这是由于吸湿层的膨胀/收缩导致微分层。使用基于水的前体溶液的胶体 MoO 表现出轻微的太阳能电池性能衰减，这也是由膨胀/收缩反应引起的，但与颗粒的面内接触和随颗粒膨胀而增加的电阻有关。然而，具有准连续和基于酒精的 MoO 的器件表现出无损的稳定电性能。
