Kinetics Of Light-induced Degradation Research Articles

Kinetics of light-induced degradation in semi-transparent perovskite solar cells

Perovskite solar cells (PSCs) have now achieved power conversion efficiencies (PCEs) over 25%, but their long-term stability under illumination and thermal stress is still a major barrier to commercialisation. Herein, we demonstrate the evaluation of light-induced degradation activation energy (Ea) of encapsulated semi-transparent PSCs by using the commonly employed method in crystalline silicon solar cells. Different parameters showed different activation energies where primary degradation is due to increase in series resistance, which also led to reduction in short-circuit current. Open-circuit voltage and shunt resistance also change with different Ea, suggesting the mechanism of the reduction is likely to be due to different reasons. Despite each parameter exhibiting slight variation over time for each temperature, the overall trend converges, indicating that each parameter is likely to be primarily reduced by a single dominant reaction. We also report the main cause of irreversible device degradation is not due to the decomposition of the perovskite layer as confirmed by X-ray diffraction characterisation. Instead, our pole figure map and absorption spectra analysis indicate that a loss of crystal symmetry occurs due to ion migration within the device that induce oxidation of 2,2′,7,7′-tetrakis-(N,N-di-4-methoxyphenylamino)-9,9′-spirobifluorene (Spiro-OMeTAD). Our work provides a better understanding through quantification of the degradation processes of encapsulated semi-transparent PSCs over time, which is essential for further progress and development of stable perovskite-Si tandem solar cells.

Kinetics of light-induced degradation in compensated boron-doped silicon investigated using photoluminescence and numerical simulation

We use photoluminescence to observe light-induced degradation in silicon in real time. Numerical simulations are used to match our results and lifetime decay data from the literature with theoretical models for the generation of the light-induced boron–oxygen defects. It is found that the existing model of the slowly generated defect SRC, where its saturated concentration is a function of the majority carrier concentration, does not explain certain results in both p- and n-type samples. A new model is proposed in which the saturated SRC concentration is controlled by the total hole concentration under illumination.

Kinetics of light-induced degradation in a-Si:H films investigated by computer simulation

In this work we investigated the stability of a-Si:H films under illumination and following recovery in darkness at different temperatures. The a-Si:H films were fabricated with 55 kHz PECVD and with conventional rf 13.56 MHz PECVD. We measured the steady-state photocurrent and the dark-current after switching off the light source as a function of time. We observed photocurrent degradation and the following recovery of the dark current. The kinetics of the photocurrent degradation as well as the dark-current recovery demonstrated stretched-exponential behavior. The results of these straightforward measurements in combination with computer simulation were used to determine the effect of light-induced degradation and thermal recovery on the density of states distribution in the band gap of a-Si:H. We have found that the photocurrent degradation and the corresponding increase in the total defect concentration have different kinetics. The different kinetics were also determined for the dark-current recovery and the corresponding decrease in the total defect concentration. The results point out that slow and fast types of defects in a-Si:H films control the kinetics of light-induced changes of the defect distribution in the band gap. A model is proposed that relates the origin of the fast and slow metastable defects with the distribution of Si-Si bond lengths.

Kinetics of Light-Induced Degradation of a-Si:H Solar Cells Compared to I-Layer Films

ABSTRACTWe report the CPM defect density of a-Si:H material and the performance characteristics of pin solar cells during high-intensity light-soaking. In one group of experiments we compared the effects of soaking with monochromatic light from a Kr+ laser to white light from a Xe arc lamp. The effects are identical for the same electron-hole pair generation rate. In a second group of experiments we light-soaked at the two different temperatures of 50°C and 90°C. At 90°C the defect density saturates at a lower value than at 50°C, and correspondingly the cell performance parameters saturate at higher values.

Light-Induced Degradation and Annealing Behaviour of Amorphous Silicon: A Comparison of Films and Devices

AbstractThe kinetics of the Staebler-Wronski effect in a-Si:H p-i-n solar cells are well known [1]. We report measurements of the kinetics of light-induced degradation and annealing of a-Si films in which we have monitored the changes in subgap absorption by means of photothermal deflection spectroscopy (PDS). The kinetics of films and cells are found to be very similar, suggesting that cell degradation is largely a material, as opposed to a device effect.

Light-induced degradation and thermal recovery of the photoconductivity in hydrogenated amorphous silicon films

Kinetics of light-induced degradation and thermal recovery of the photoconductivity in hydrogenated amorphous silicon have been investigated. Rate equations for these processes were derived using the principles of reaction rate theory. Both degradation and recovery were found to be thermally activated with activation energies of 0.1 and 1.35 eV, respectively. Experimental results support the bond breaking model for the degradation. Stabilization of broken bonds is achieved by structural relaxation. Thermal recovery proceeds through hydrogen hopping from one dangling bond to another. Experimental evidence suggests the existence of an upper limit in the density of light-induced defects. A microscopic model, consistent with experimental observations, is proposed for the light-induced generation and thermal recovery of defects in a-Si:H.