Discriminating bulk versus interface shunts in organic solar cells by advanced imaging techniques

Abstract

An important aspect when upscaling organic photovoltaics from laboratory to industrial scale is quality control. Established imaging techniques like lock‐in thermography or luminescence imaging are frequently used for this purpose. While these techniques allow for the lateral detection of defects, they cannot provide information on the vertical position of the defect in the OPV stack. Here, we present an approach to overcome this limitation. A femtosecond‐laser is deployed to introduce well‐defined artificial calibration defects selectively into both the interface and the bulk active layer of inverted P3HT:PCBM bulk heterojunction cells during device fabrication. The defective cells are then characterized using J‐V analysis and several nondestructive imaging methods (dark lock‐in thermography, photoluminescence, and electroluminescence imaging). The distinct response for each defect in the different imaging methods enables us to uniquely distinguish between bulk and interface defects. This allows to study surface recombination under most controlled conditions.

Accelerating organic solar cell material's discovery: high-throughput screening and big data

“…6 After generation of the combinatorial libraries, compatible characterization methodologies include (a) Raman spectroscopy imaging, which serves to quantify active layer thickness and composition variations over large areas; 70 (b) photocurrent imaging, which can be performed using either a focused laser beam source 27,54,70 or a movable shadow mask to illuminate controlled portions of the sample while extracting the corresponding J sc ; 63 (c) liquid-metal top electrodes in devices without evaporated top electrodes, having the intrinsic advantage of extracting local JV curves throughout the combinatorial library; 64 and (d) a combination of dark lock-in thermography (DLIT) and luminescence imaging (including electroluminescence, EL, and photoluminescence, PL) to evaluate the presence of defects in any of the interlayers forming the OPV device stack. 76 View Article Online in fully operational devices. Likely, it is simply a matter of time for these techniques to be eventually exploited in conjunction with combinatorial parametric libraries in high-throughput experiments based on lateral gradients.…”

“…6d ). 76 For that reason, they are natively fast evaluation techniques compatible with large area devices that keep an excellent sample preservation. When applied to lateral parametric gradients or libraries, these techniques can be leveraged as qualitative imaging tools in high-throughput experiments despite not being able to quantify their lateral distribution, such as thickness or composition (as Raman spectroscopy does).…”

Fast and Nondestructive Failure Analysis of Organic Photovoltaic Modules for Low‐Light Harvesting: Coupling Variable Illumination Measurements to Electroluminescence Imaging

“…EL imaging is a method of choice for localization of defective cells having high surface recombination due to either nonoptimized work function of interface layer, [53] low series resistance due to nonoptimized TCO or interface layer, [54][55][56][57] or low parallel resistance due to the presence of short circuits. [32,58] Luminescence is produced once injected current reaches the AL. In low R p cells, current will preferably flow through shunt paths without reaching the AL, and no luminescence will be emitted.…”

“…In addition to that, in OPV as well as in other PV fields, such as thin films and crystalline silicon, shunts have been commonly tracked using dark lock-in thermography and luminescence imaging. [24][25][26][27][28][29][30][31][32] Still, these approaches were not intended for low-light performance optimization but rather for device optimization under 1 sun [24][25][26][27][28][29][30][31][32] or in aging studies. [33][34][35] Furthermore, among the wide range of diagnosis tools developed for PV devices, electrical modeling approaches have been developed.…”

From Straw to Device Interface: Carboxymethyl‐Cellulose‐Based Modified Interlayer for Enhanced Power Conversion Efficiency of Organic Solar Cells

“…Generally, organic materials are synthesized easily with high electron mobility and tunable bandgap energy. Some of them (poly[(9,9‐bis(3′‐( N , N ‐dimethylamino)propyl)‐2,7‐fluorene)‐ alt ‐2,7‐(9,9‐dioctyfluorene)], polyethylenimine, and polyethylenimine ethoxylated (PEIE)) were found to be effective interface modifiers with matched performance of these devices, compared to the devices using conventional interlayer materials (Ca/Mg) . However, these organic electrolytes have complicated structures with difficult synthetic procedure.…”