Abstract
AbstractOrganic tandem solar cells recently made great improvements with power conversion efficiencies (PCEs) over 15%, making them attractive for further large‐scale production and industrial applications. However, compared to their single‐junction counterparts, the complicated device architectures of organic tandem solar cells strongly restrict their processing and upscaling to larger scales. Therefore, fast and reliable quality control measures are crucial for developing organic tandem photovoltaic technologies towards commercialization. Some of the most widely used means for quality control are luminescence imaging and lock‐in thermography respectively. While effective techniques, they are limited in some respects. For example, determining the lateral position of a defect is easily possible, while the exact resolution in which layer of a thin film stack a defect is located, is challenging. This is particularly the case for tandem cells with complicated multi‐layer cell architectures. This approach to overcome this challenge is the introduction of well‐defined artificial defects into certain layers of an organic tandem cell stack and subsequently performing imaging analysis of the defected cells with several complementary methods. The unique response from cells with artificial defects using different imaging techniques and excitation sources can then be transferred to the imaging of devices with naturally occurring manufacturing defects.
Highlights
Introduction adjusting the production process To this end, a multitude of different imaging methods can Recent developments show a dramatic increase in the power con- be used to find defects and their position on a sample
Between 1 and 3 defects have been introduced into the samples, leading to a defective area between roughly 1% and 5% of the complete cell area
The defected samples were investigated by standard J–V analysis and by electroluminescence imaging (EL), dark lock-in thermography (DLIT) and photoluminescence imaging (PL)
Summary
The first investigated defects are concerning the interface layers between electrode and photoactive layer, namely the electron transport layer (ETL) on top of the bottom electrode (ITO) and the hole transport layer (HTL) below the top electrode (Ag). The J–V curves show practically no difference between the defective cell and the reference cell, which clearly indicates that these type of interface defects do not lead to obvious power dissipation for small amounts of defective area (up to ≈5% tested). This is similar to the effects observed for laser defects in the ETL of single-junction OSCs.[54] the effect on the images is practically the same, with a general reduction of the DLIT and the EL signal at the defect positions due to an increased barrier for charge injection at the ITO/AL interface in comparison to the ITO/ETL/AL interface. While the reason for this increase in radiative recombination for one of the layers at the defect position is not completely clear, it could be used to clearly distinguish between top and bottom interface defects, at least for this system
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