Enhancing the stability of Organic Photovoltaics through Machine Learning

A machine learning approach for extracting information from organic photovoltaic (OPV) solar cell data is presented. A database consisting of 1850 entries of device characteristics, performance and stability data is utilised and a sequential minimal optimisation regression (SMOreg) model is employed as a means of determining the most influential factors governing the solar cell stability and power conversion efficiency (PCE). This is achieved through the analysis of the acquired SMOreg model in terms of the attribute weights. Significantly, the analysis presented allows for identification of materials which could lead to improvements in stability and PCE for each thin film in the device architecture, as well as highlighting the role of different stress factors in the degradation of OPVs. It is found that, for tests conducted under ISOS-L protocols the choice of light spectrum and the active layer material significantly govern the stability, whilst for tests conducted under ISOS-D protocols, the primary attributes are material and encapsulation dependent. The reported approach affords a rapid and efficient method of applying machine learning to enable material identification that possess the best stability and performance. Ultimately, researchers and industries will be able to obtain invaluable information for developing future OPV technologies so that can be realised in a significantly shorter period by reducing the need for time-consuming experimentation and optimisation

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

Enhancing the stability of perovskite solar cells through functionalisation of metal oxide transport layers with self-assembled monolayers

A systematic study of the application of self-assembly monolayers (SAMs) onto electron and hole transporting layers for perovskite solar cells (PSCs) stability is reported. Cs0.05FA0.83MA0.17Pb(I0.87Br0.13)3 (FMC) perovskite films were deposited onto tin oxide (SnO2) and nickel oxide (NiOx) layers that were functionalized with ethylphosphonic acid (EPA) and 4-bromobenzoic acid (BBA) SAMs. X-ray diffractometry measurements were performed on these films shortly after they were deposited. The diffractograms agree with the positions reported in the literature for the crystal structure of the FMC. The results show that the deposition of SAMs on the metal oxide layers yields positive improvements in the FMC film stability and in the device stability when using FMC as the active layer. The work shows that by adopting SAMs, the long-term stability of PSCs cells under accelerated test conditions can be enhanced, and this provides one step on the way to making this technology a commercial reality

Application of luminescence downshifting materials for enhanced stability of CH3NH3PbI3(1-x)Cl3x perovskite photovoltaic devices

The application of luminescent down shifting (LDS) layers as alternative UV filters for CH3NH3PbI3(1-x)Cl3x perovskite solar cell (PSC) devices is reported. A combination of photo-absorption measurements and of device decay measurements during light soaking are used to verify the stability. The application of a UV filter or LDS layer was able to significantly retard photo-induced degradation with ∼18% drop in device power conversion efficiency (PCE) observed over 30 h for non-encapsulated devices, which is compared to ∼97% for an un-filtered device, also without encapsulation. Whilst the PCE of the PSC device decreases with the application of the LDS layer, the drop is not as significant as when a commercial UV filter is used. Considering that UV filters will be essential for the commercialization of PSCs, the work provides evidence that the LDS layer can act as an alternative UV filter in PSCs and can limit the drop in PCE that can be expected from the inclusion of a UV filter, thus providing an added benefit over commercial UV filters