Cu2ZnSnSe4solar cells with 10.6% efficiency through innovative absorber engineering with Ge superficial nanolayer

Learning from nature for healthcare, energy, and environment

An essential scientific and practical problem of sustainable development of the country’s energy sector is predicting the parameters and foreseeing the conditions of functioning of solar cells and solar elements in normal and emergency situations. It is emphasized that this allows to provide solar energy with high efficiency indicators, including return on invested capital in the solar panels construction. The main specific research method used is regression analysis aimed at building a model for predicting the total amount of generated energy from solar cells in ground-based installations under variable conditions. The distribution of the model output data by the number of solar cell modules is analyzed on the example of ground-mounted solar installations. To obtain empirical data, we selected 31 facilities in the Dnipro and Zaporizhzhia regions that use solar cells with different numbers of modules. This allows to calculate the weighted average amount of energy generated during operation in variable conditions. We distinguished 10 intervals of frequency values, with the largest range of values being in the range of 10000-20000 solar cell modules. The regression coefficients were checked by two criteria. According to the criterion of “t-statistics value”: the coefficients are significant at a significance level of 0.05. The criterion of asymptotic significance determines the rejection of the null hypothesis in a statistical test. The random value is 170.3694, which is significantly higher than the critical value of the F-statistic of 3.33. A model of the dependence of the total amount of generated energy on the number of solar modules and the weighted average amount of generated energy was built on the basis of regression analysis. It is determined that the model influence factor “number of solar modules” has a positive effect on the resultant factor (solar cell productivity). Whereas the influence factor is “weighted average amount of generated energy”. However, the influence factor “number of solar modules” is more significant. The obtained results allow us to assert the possibility of their implementation in the energy sector.

By bringing together a systematic IV-characterization and EDMR experiments, transport and degradation processes were studied in organic devices. In a first step, two Zinc phthalocyanine (ZnPc) single layer devices with different electrodes were investigated, a coplanar Au/ZnPc/Au sample and a sandwich type ITO/ZnPc/Al device. They served as a testbed for the correlation of IV- and EDMR measurements. The insights gained in this study were then applied to more complex bilayer ZnPc/C60-heterojunction solar cells. A transport study at low voltages shows that bulk transport with Ohmic IV characteristics is dominant in the coplanar ZnPc, whereas the transport in the sandwich device is controled by a Schottky barrier at the aluminum contact. Both samples show SCL-currents with exponential trap distribution in the high voltage limit, characteristic for ZnPc. The degradation analysis indicate that the ITO/ZnPc/Al - device suffers from oxidation of the aluminum electrode, exhibiting a pronounced Schottky emission IV-behavior. This degradation could be prevented by an effective encapsulation, using a glass cover and UV-glue. The results of the solar cells also indicate an oxygen-induced degradation. This degradation is related to an increase of the resistivity in the C60 layer, due to oxygen impurities. The EDMR measurements indicate that polaron recombination is the dominant process in the organic devices investigated in this work. However the recombination process shows distinct impact on the electric transport in the individual devices. Whereas the EDMR signal is photocurrent quenching in the coplanar sample it reverses sign in the sandwich device. The results of the transport measurements indicate a charge accumulation at the oxidized ZnPc/Al contact. As a consequence a model was proposed in which recombination involving these accumulated carriers can lead to a current enhancement. This model was verified by voltage dependent EDMR measurements, where it consistently explains a sign reversal when changing from negative to positive bias. In degraded solar cells a similar charge accumulation as in the ZnPc-layer is suspected. This charge accumulation manifests itself in an EDMR signal with identical properties to the one in ZnPc and is assumed to happen at the ZnPc/C60- interface, during degradation. Furthermore, EDMR studies indicate that spin-dependent recombination happens during the exciton dissociation process at the ZnPc/C60 - interface, in the charged transfer complex (ZnPc+, C60-). This process is observed to quench the photocurrent in the solar cells. In further spin studies Rabi beat oscillations under spin-locking conditions were observed for the first time in the EDMR of ZnPc and solar cells. This phenomenon exhibits a signal oscillation at twice the Rabi-frequency that appears only when two pair spins are excited at the same time. The impact of this beat oscillation on EDMR lineshapes as well as its microwave power dependence were studied in detail. The effect of exchange coupling in the spin-pair was analyzed in the context of the beat oscillations and a lock in phase analysis.

Synthesis of in-gap band CuGaS2:Cr absorbers and numerical assessment of their performance in solar cells

Effects of alkali-metal incorporation into epitaxial Cu(In,Ga)Se2 solar cells prepared by molecular beam epitaxy

Trapping light inside the solar cells can significantly boost their efficiency by minimizing the reflection losses at the front interface as well as the absorption losses in the solar cell by increasing the path length of incoming light. This study focuses on light trapping using antireflection coating (ARC). One of the simplest and most efficient types of ARC is called the quarter-wave transformer. Its great results make it a good and cheaper alternative for using metallic nanoparticles (MNPs). However, using MNPs with appropriate parameters might have a positive effect on the overall enhancement. In this work it was found that placing the NPs on the ARC surface give the best results compared to the other positions, whereas decreasing the overall refractive index of the device improves its behavior.

The performance of polymer solar cells is strongly dependent on the morphology of the photoactive layer, which can be optimized by tuning the polymer side chain pattern. Whereas most studies focus on length and bulkiness, the side chain density receives much less attention. In this work, the effect of the number of side chains on PCPDTQx(2F) low bandgap copolymers on material properties and solar cell characteristics is investigated. The active layer morphology is strongly affected, affording more favorable finely intermixed blends when decreasing the side chain density. As a result, the efficiency increases to a maximum of 5.63% for the device based on the copolymer with intermediate side chain density. Moreover, removal of the side chains also has a positive effect on device stability under prolonged thermal stress. A single structural parameter—alkyl side chain density—is hence used for simultaneous enhancement of both solar cell efficiency and lifetime

Effect of iodine intercalation in nanosized layered double hydroxides for the preparation of quasi-solid electrolyte in DSSC devices

The long-term stability of solar cells is a crucial factor for the competitiveness of a technology. In this study, the accelerated aging of CIGS solar cells was studied, and the influence of an applied bias during the endurance test on the open-circuit voltage V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oc</inf> and fill factor (FF) was investigated. Time constants for parameter drifts of the open-circuit voltage and the associated activation energy were determined. The observed parameter drifts will be discussed, and a model will be proposed based on SCAPS simulations, explaining the observed behavior of the electrical characteristics of the solar cells. Therefore, cells were dark annealed under dry conditions at two different temperatures and different voltage biases were applied to the cells. Our study revealed that the application of a positive bias, which is similar to light soaking, first leads to an improvement and stabilization of the open-circuit voltage and FF followed by a slow decrease of these parameters. This long-term decrease can be explained in terms of a back barrier or phototransistor, as simulated with SCAPS. However, applying a positive bias enhances the long-term stability of these devices. The appearance of a back barrier is associated with a time constant exceeding 30 years. Therefore, this degradation mechanism is not critical.

Incorporation of a small amount of sodium into Cu(In,Ga)Se2 (CIGS) absorbers for thin-film solar cells is well known to enhance conversion efficiencies. Usually, Na is added in a way such that it is present during CIGS growth and therewith influences the growth kinetics. We have used post-deposition Na in-diffusion into as-grown, Na-free absorbers and observed typical efficiency improvements. This suggests that in general the main positive Na effect originates from changes in the electronic absorber properties rather than from modification of CIGS growth kinetics. At low substrate temperatures, Na impedes CIGS phase formation. This may explain why absorbers grown at substrate temperatures below 450°C in the presence of Na yield inferior cells compared with post-deposition-treated CIGS. We have developed post-deposition Na incorporation for the processing of flexible CIGS solar cells on polyimide substrates. A conversion efficiency of 14.1% under AM1.5 standard test conditions was independently measured. This represents the highest reported efficiency of any solar cell grown on a polymer substrate to date.

Growth of p-CdTe thin films on n-GaN/sapphire

Influence of an ammonia activation prior to the PECVD SiN deposition on the solar cell performance

Theoretical design of thiazolothiazole-based organic dyes with different electron donors for dye-sensitized solar cells

The competing roles of i-ZnO in Cu(In,Ga)Se2 solar cells

This paper focuses on the influence of the effective intra-grain minority charge carrier diffusion length and surface recombination velocity at grain boundaries on solar cell parameters. Both can be extracted in principle from Light- and Electron Beam Induced Current measurements (LBIC and EBIC). Multicrystalline floatzone (mc FZ) silicon with different grain sizes was processed to solar cells with and without hydrogenation step, followed by LBIC and EBIC characterization. A theoretical model is used which can be applied to measured LBIC or EBIC profiles in order to obtain values for the effective intra-grain diffusion length and the recombination velocity at grain boundaries. Efficiencies reached on the processed solar cells (up to 16.0%) are the highest reported so far for material with such a small grain size, and the positive effect of hydrogenation can clearly be seen. The obtained results are very useful for other cost effective small grained mc silicon materials.