Wiljan Verhees

Accurate efficiency determination and stability studies of conjugated polymer/fullerene solar cells

We report on an accurate indoor determination of the power conversion efficiency under standard test conditions w1000 Wy m, 2 AM1.5 global (IEC 904-3) ,2 58Cx for an organic photovoltaic device based on a bulk heterojunction of a conjugated polymer and a methanofullerene. AM1.5 efficiencies up to 2.55% are achieved for cell areas F1.0 cm . Systematic stability studies on 2

Kinetic competition in liquid electrolyte and solid-state cyanine dye sensitized solar cells

The photovoltaic performance of liquid electrolyte and solid-state dye sensitized solar cells, employing a squarilium methoxy cyanide dye, are evaluated in terms of interfacial electron transfer kinetics. Dye adsorption to the metal oxide film resulted in a mixed population of aggregated and monomeric sensitizer dyes. Emission quenching data, coupled with transient absorption studies, indicate that efficient electron injection was only achieved by the monomeric dyes, with the aggregated dye population having an injection yield an order of magnitude lower. In liquid electrolyte devices, transient absorption studies indicate that photocurrent generation is further limited by slow kinetics of the regeneration of monomeric dye cations by the iodide/iodine redox couple. The regeneration dynamics are observed to be too slow (≫ 100 µs) to compete effectively with the recombination of injected electrons with dye cations. In contrast, for solid-state devices employing the organic hole conductor spiro-OMeTAD, the regeneration dynamics are fast enough (≪ 1 µs) to compete effectively with this recombination reaction, resulting in enhanced photocurrent generation.

High-efficiency humidity-stable planar perovskite solar cells based on atomic layer architecture

Perovskite materials are drawing tremendous interest for photovoltaic solar cell applications, but are hampered by intrinsic material and device instability issues. Such issues can arise from environmental influences as well as from the chemical incompatibility of the perovskite layer with charge transport layers and electrodes used in the device stack. Several attempts have been made to address the instability issue, mostly concentrating on the substitution of the organic cations in the perovskite lattice, and on alternatives for the organic charge extraction layers, without laying much emphasis on stabilising the existing, conventional high efficiency methylammonium lead iodide/spiro-OMeTAD based devices. To address the latter issue, we utilized atomic layer deposition (ALD) as a straightforward and soft deposition process to conformally deposit Al2O3 on top of the perovskite absorber. An ultra-thin ALD Al2O3 film effectively protects the perovskite layer while it is sufficiently thin enough to provide a tunnel contact. The fabricated perovskite solar cells (PSCs) exhibit superior device performance with a stabilised power conversion efficiency (PCE) of 18%, a significant reduction in hysteresis loss, and enhanced long-term stability (beyond 60 days) as a function of the unencapsulated storage time in ambient air, under humidity conditions ranging from 40 to 70% at room temperature. PCE measurements after 70 days of humidity exposure show that the devices incorporating 10 cycles of ALD Al2O3 could significantly retard the humidity-induced degradation thereby retaining about 60–70% of its initial PCE, while that of the reference devices drops to a remaining 12% of their initial PCE. This work successfully addresses and tackles the problem of the hybrid organic–inorganic IV-halide perovskite solar cell’s instability in a humid environment, and the key findings pave the way to the upscaling of these devices.

Towards the scaling up of perovskite solar cells and modules

A direct current (DC) simulation for perovskite solar cells with different dimensions was performed. The theoretical results demonstrate a good agreement with experimental data, indicating the reliability of the performed simulation. A theoretical model was applied for the investigation of large area devices with different sheet resistances of the transparent electrodes. The results indicate the critical influence of electrode resistance on the performance with the upscaling of the active area of the devices. The performance of the perovskite modules, calculated using DC simulation, enables the identification of the most rational sub-cell dimensions in the modules. The presented results reveal the relationship between the power conversion efficiency (PCE) of the devices and the dimensions of the active area or the width of the sub-cell in the module. The DC simulation allows the determination of the optimal cell dimensions suitable for the upscaling of perovskite modules on substrates with different sheet resistances of the transparent electrodes.

Describing the light intensity dependence of polymer:fullerene solar cells using an adapted Shockley diode model

Solar cells are generally optimised for operation under AM1.5 100 mW cm(-2) conditions. This is also typically done for polymer solar cells. However, one of the entry markets for this emerging technology is portable electronics. For this market, the spectral shape and intensity of typical illumination conditions deviate considerably from the standard test conditions (AM1.5, 100 mW cm(-2), at 25 °C). The performance of polymer solar cells is strongly dependent on the intensity and spectral shape of the light source. For this reason the cells should be optimised for the specific application. Here a theoretical model is presented that describes the light intensity dependence of P3HT:[C60]PCBM solar cells. It is based on the Shockley diode equation, combined with a metal-insulator-metal model. In this way the observed light intensity dependence of P3HT:[C60]PCBM solar cells can be described using a 1-diode model, allowing fast optimization of polymer solar cells and module design.

Highly Efficient and Stable Flexible Perovskite Solar Cells with Metal Oxides Nanoparticle Charge Extraction Layers

In this study, the fabrication of highly efficient and durable flexible inverted perovskite solar cells (PSCs) is reported. Presynthesized, solution-derived NiOx and ZnO nanoparticles films are employed at room temperature as a hole transport layer (HTL) and electron transport layer (ETL), respectively. The triple cation perovskite films are produced in a single step and for the sake of comparison, ultrasmooth and pinhole-free absorbing layers are also fabricated using MAPbI3 perovskite. The triple cation perovskite cells exhibit champion power conversion efficiencies (PCEs) of 18.6% with high stabilized power conversion efficiency of 17.7% on rigid glass/indium tin oxide (ITO) substrates (comparing with 16.6% PCE with 16.1% stabilized output efficiency for the flexible polyethylene naphthalate (PEN)/thin film barrier/ITO substrates). More interestingly, the durability of flexible PSC under simulation of operative condition is proved. Over 85% of the maximum stabilized output efficiency is retained after 1000 h aging employing a thin MAPbI3 perovskite (over 90% after 500 h with a thick triple cation perovskite). This result is comparable to a similar state of the art rigid PSC and represents a breakthrough in the stability of flexible PSC using ETLs and HTLs compatible with roll to roll production speed, thanks to their room temperature processing.

Recombination kinetics of interpenetrating heterojunctions: comparison of dye sensitized and polymer solar cells

Over the last few years, measurements from many labs have allowed the development of a reasonably complete picture of the kinetics and electrostatics (band alignments and fields) of dye sensitized solar cells based on nanoporous oxide films (e.g. TiO/sub 2/, ZnO). With some modifications, this model incorporates both electrolyte and solid-state versions of dye sensitized cells. However, there are still several key features which are not yet understood. This paper discusses briefly the relationship or lack thereof between the recombination rate constant and the electron concentration (DOS) for a wide variety of nanostructured photovoltaic cells.