Multi stress testing of OPV modules for accurate predictive ageing and reliability predictions

Organic photovoltaic (OPV) degradation remains a complex challenge and previous studies have shown the degradation to be a function of multiple stresses, so it can be inaccurate to predict failure rates using single stress tests. In this paper, a new testing methodology whereby multiple stresses are applied simultaneously using a “design of experiment (DOE) approach” is reported and used for predictive aging of modules. Multistress data are used for predictive aging of OPV modules under different stress levels; a general log-linear life model has been adapted and applied in order to predict the life of OPV modules and this is compared to experimental data, which show that a close estimation of simulated lifetime is obtained (within 18% accuracy). The life test models can be used for predicting aging of OPV modules in different geographic locations and could be used to account for different degradation rates due to seasonal climatic variations. Furthermore, by using the DOE data, we show how the major stress factors can be screened and their statistical significance upon degradation quantified using analysis of variance. One of the potential benefits of using this approach for OPV degradation studies is that additional factors could be added to study the impact on degradation to provide a more comprehensive study

Multivariate Approach for Studying the Degradation of Perovskite Solar Cells.

Despite the progress in the performance of perovskite solar cells (PSCs), the absorber layer degradation during prolonged exposure to multiple environmental conditions is still a major issue. As the degradation depends upon many intrinsic and extrinsic factors, the need to adopt a multivariate testing protocol, which provides rapid assessment of device stability, is required. To do this, a Plackett Burman (PB) screening design has been used to analyze 9 different factors that affect the PSC stability; including four extrinsic factors (oxygen, moisture, UV exposure and temperature) and five intrinsic factors (selection of hole transport layer and electron transport layer, absorber layer thickness, halide type and perovskite deposition process). This approach allows us to rank the relative severity of these factors and can be used to narrow the scope of materials and device architectures to be modified, by identifying materials and configurations, which are the most stable. The least and most stable device configurations have been identified and the success of the screening approach has been demonstrated by testing the optimized configurations under ISOS-D1 and –L2 protocols. Importantly, only 12 experiments are needed to establish the most stable combination from the 9 factors thus providing a rapid assessment. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) measurements of perovskite absorber films have been performed in order to understand the degradation pathways and to support the conclusion of PB screening technique

Spray coated silver nanowires as transparent electrodes in OPVs for Building Integrated Photovoltaics applications

The application of spray coated silver nanowires (AgNWs) onto OPVs for building Integrated Photovoltaics (BIPVs) is demonstrated. By using AgNWs with PEDOT:PSS, a transparent conductive layer was demonstrated on top of an P3HT:PCBM active layer with a sheet resistance of 30 Ω/⎕ for 90% transparency. This has been applied to two separate configurations; semi-transparent OPVs for solar glazing applications and OPVs onto an opaque substrate, namely steel. For the latter, a novel technique to planarise the steel substrate with an intermediate layer is also presented, with a substantial decrease in surface roughness reported to ensure that the substrate is smooth enough to use for OPV fabrication. The use of SU-8 as an intermediate layer reduced the surface roughness to RA=10 nm, which is one of the lowest values reported to date, and was achieved on a low cost substrate (DC01 low carbon steel) using solution processing

Using ISOS consensus test protocols for development of quantitative life test models in ageing of organic solar cells

As Organic Photovoltaic (OPV) development matures, the demand grows for rapid characterisation of degradation and application of Quantitative Accelerated Life Tests (QALT) models to predict and improve reliability. To date, most accelerated testing on OPVs has been conducted using ISOS consensus standards. This paper identifies some of the problems in using and interpreting the results for predicting ageing based upon ISOS consensus standard test data. Design of Experiments (DOE) in conjunction with data from ISOS consensus standards are used as the basis for developing life test models for OPV modules. This is used to study their temperature-humidity and light-induced degradation, which enables failure rates during accelerated testing to be assessed against the typical outdoor operational conditions. The life test models are used to assess the relative severity of the ISOS standards and the impact of geographic and seasonal climatic changes on OPV degradation

Outdoor performance monitoring of perovskite solar cell mini-modules: Diurnal performance, observance of reversible degradation and variation with climatic performance

The outdoor performance monitoring of two types of perovskite solar cell (PSC) mini-modules based on two different absorbers - CH3NH3PbI3 (MAPI) and Cs0.05FA0.83MA0.17PbI(0.87Br0.13)3 (FMC) is reported. PSC modules displayed markedly different outdoor performance characteristics to other PV technologies owing to the reversible diurnal changes in efficiency, difference in temperature coefficient between absorber layers and response under low light conditions. Examination of diurnal performance parameters on a sunny day showed that whereas the FMC modules maintained their efficiency throughout the day, the MAPI modules peaked in performance during the morning and afternoon, with a strong decrease around midday. Overall, the MAPI modules showed a strongly negative temperature coefficient (TC) for PCE, whereas the FMC modules showed a moderate positive temperature coefficient performance as a function of temperature due to the increase in JSC and FF. Outdoor monitoring of the MAPI modules over several days highlighted that the reduced over the course of the day but recovered overnight. In contrast the FMC modules improved slightly during the daytime although this was too reversed overnight. This paper provides insight into how PSC modules perform under real-life conditions and consider some of the unique characteristics that are observed in this solar cell technology

Enhancing fully printable mesoscopic perovskite solar cell performance using integrated metallic grids to improve carbon electrode conductivity

Carbon based Perovskite Solar cells (C–PSCs) have emerged as the most promising candidates for commercialisation in the field of perovskite photovoltaics, as they are highly stable, low cost and make use of easily scaled manufacturing techniques. However, the limited conductivity of the carbon electrode inhibits performance and represents a significant barrier to commercial application. Τhis work presents a scalable method for enhancing the carbon electrode conductivity through the integration of aluminium and copper grids into prefabricated C–PSCs. Adhered to the cells using an additional low temperature carbon ink, the metallic grids were found to dramatically reduce top electrode series resistance, leading to a large improvement in fill factor and efficiency. After grid integration, the 1 cm2 C–PSCs yielded power conversion efficiency (PCE) of 13.4% and 13% for copper and aluminium respectively, while standard C–PSCs obtained PCE of 11.3%. Performance is also significantly augmented in the case of larger-scale 11.7 cm2 modules, where PCEs went from 7.7% to 10% and 11% for aluminium and copper grids respectively. This technique offers a fast and low temperature route to high-performance, large-area C–PSCs and could therefore have serious potential for application to the high-volume manufacture of perovskite cells and modules

Development of multidye UV filters for OPVs using luminescent materials

Luminescence down-shifting (LDS) is used in several photovoltaic technologies aiming to improve the photon conversion efficiency (PCE) of the devices through the increase of the light harvesting in the regions of the electromagnetic spectrum where the EQE of the solar cells is poor. The aim of this work was to produce films of mixtures (blends) of two luminescent materials, dispersed in a poly-methyl methacrylate (PMMA) matrix, hoping to improve their properties both as LDS layer and as UV filter when applied on the clear, external surface of P3HT:PC61BM photovoltaic devices. The best results led to an increment of 7.4% in the PCE of the devices, and a six fold enhancement in their half-life (T50%). This study indicates that multidye LDS layers with optimized optical properties can lead to an effective improvement in the performance and operational stability of OPVs

Mixed dimension silver nanowires for solution processed, flexible, transparent and conducting electrodes with improved optical and physical properties

This is an author-created, un-copyedited version of an article accepted for publication in Flexible and Printed Electronics. The publisher is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at http://doi.org/10.1088/2058-8585/aa6011.In this work, we present an alternative method for the spray coating of silver nanowires contact electrodes by employing a mixture of short and long nanowires. Mixed silver nanowires are found to give improve optical properties with 2-5% higher transparency for the same sheet resistance of 25 Ωsq-1, when compared to silver nanowires prepared with a single geometry nanowire. The figure of merit (FoM) for the 25 Ωsq-1 sheet resistance electrode was found to be highest for the mixed composition AgNWs-M1 based electrodes. Furthermore, the average root mean square surface roughness (Rq) parameter by WLI measurement are found to be lower for the mixed composition silver nanowires electrodes (Rq= 3-4 nm) when compare to the individual parent fixed dimension type silver nanowire electrodes (Rq = 6-8 nm)