Department of Chemical and Biological Engineering, Princeton University, Princeton, New Jersey 08544, USA.
Langmuir. 2011 Sep 6;27(17):11265-71. doi: 10.1021/la202178p. Epub 2011 Aug 5.
The ability to laminate and delaminate top metal contacts during the processing and testing of inverted polymer solar cells has led us to uncover the peculiar dependence of their open-circuit voltage (V(oc)) on the annealing sequence. Specifically, thermally annealing inverted polymer solar cells having bulk-heterojunction photoactive layers after top electrode deposition above 100 °C leads to lower V(oc) compared to analogous devices with unannealed photoactive layers or photoactive layers that have been annealed prior to metal electrode deposition. This reduction in V(oc), however, can be reversed when the top electrodes are replaced. This observation is thus a strong indication that such changes in V(oc) with annealing sequence are manifestations of changes at the top electrode-photoactive layer interface, and not structural changes in the bulk of the photoactive layer. Electronic characterization conducted on the photoactive layers and metal contacts after dissection of the polymer solar cells via delamination suggests the reduction of V(oc) on thermal annealing in the presence of the metal top contacts to stem from an interfacial chemical reaction between the photoactive layers and the metal electrodes. This chemically generated interfacial layer is removed upon electrode delamination, effectively reverting the V(oc) to its original value prior to thermal annealing when the top electrodes are replaced.
在倒置聚合物太阳能电池的加工和测试过程中，对顶部金属接触进行层压和去层压的能力使我们发现了它们的开路电压 (V(oc)) 对退火顺序的特殊依赖性。具体来说，在顶部电极沉积后，将具有体异质结光活性层的倒置聚合物太阳能电池在 100°C 以上进行热退火会导致 V(oc) 降低与未经退火的光活性层或在金属电极沉积之前已退火的光活性层的类似器件相比。然而，当更换顶部电极时，这种 V(oc) 的降低可以得到逆转。因此，这种观察结果强烈表明，V(oc) 随退火顺序的这种变化是顶部电极-光活性层界面变化的表现，而不是光活性层体中的结构变化。通过剥离对聚合物太阳能电池进行剖析后，对光活性层和金属接触进行的电子特性分析表明，在金属顶部接触存在的情况下进行热退火时 V(oc) 的降低源于光活性层和金属电极之间的界面化学反应。在去除电极后，当更换顶部电极时，该化学产生的界面层被去除，有效地将 V(oc) 恢复到热退火之前的原始值。
