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Polycrystalline Cu In,Ga Se2 CIGSe thin film solar cells exhibit gradual onset in their external quantum efficiency EQE spectra whose shape can be affected by various CIGSe material properties. Apart from influences on the charge carrier collection, a broadening of the EQE onset leads to enhanced radiative losses in open circuit voltage Voc . In the present work, Gaussian broadening of parameters describing the EQE onset of thin film solar cells, represented by the standard deviation, amp; 120590;total, was evaluated to study the impacts of the effective band gap energy, the electron diffusion length, and the Ga In gradient in the CIGSe absorber. It is shown that amp; 120590;total can be disentangled into contributions of these material properties, in addition to a residual component amp; 120590;residual. Effectively, amp; 120590;total depends only on a contribution related to the Ga In gradient as well as on amp; 120590;residual. The present work highlights the connection of this compositional gradient, the microstructure in the polycrystalline CIGSe absorber, and the luminescence emission with the residual component amp; 120590;residual. It is demonstrated that a flat band gap with no compositional gradient in the bulk of the CIGSe absorber is essential to obtain the lowest amp; 120590;total values and thus result in lower recombination losses and gains in Voc

37th European Photovoltaic Solar Energy Conference and Exhibition; 718-721, This work presents the adaptation of post-deposition treatments with sodium fluoride and/or rubidium fluoride, as previously developed for our multi-source co-evaporated absorbers, to sequentially prepared Cu(In,Ga)(S,Se)2 (CIGSSe) thin-films using fast atmospheric pressure chalcogenization of sputtered precursors. The incorporation of the alkali metals into the films with different Cu/(Ga+In) (CGI) ratios and their effect on material and device properties is analyzed and compared to findings obtained for multi-source co-evaporated absorbers. It was found that a Mo(S,Se)X layer at the back contact of the sequentially prepared films possibly acts as a sink for alkali ions, leading to in-depth distributions of alkali metals that differ from those in absorbers prepared by co-evaporation. The best device results were obtained with a sequentially prepared CIGSSe sample with CGI=0.87, using a NaF followed by a RbF-PDT, and resulted in a maximum VOC ≈ 600 mV and a VOC deficit of around 400mV. Additionally, the FF was enhanced. Ultimately, by using photolithographic cell definition and a MgF2 anti-reflective coating, the NaF+RbF PDT resulted in solar cells with independently certified efficiencies of up to 18.4%, a significant improvement of the previous value without PDT. At this early development stage, these results demonstrate that the PDT is useful to exploit the potential of absorbers prepared by fast, vacuum-free processing.

37th European Photovoltaic Solar Energy Conference and Exhibition; 627-632, For optimum design and accurate yield prediction, it is required to know the parameters of a photovoltaic module as a function of module temperature and irradiation. The commonly available values within the data sheet, such as parameters under STC, temperature coefficients at STC and low light performance at a fixed irradiation, will give a first but not very precise estimation of module parameters at arbitrary irradiation and temperature. We propose a new algorithm that, in contrast to some of the existing approaches, provides equations not only for the maximum power point (Pmpp) output, but also for open circuit voltage, short circuit current, and current at MPP. It uses only a minimum of initial assumptions concerning the module behavior (black box model) which should make it universally applicable for different solar cell technologies. On the other hand, by comparing the black box equations to analytical descriptions of CIGSSe solar cells, we can cross-link both models and derive device physics parameters from the black box representation. Comparison of model based prediction and actual outdoor data collected over several months in Berlin confirms that the black box model offers a simple and intuitive method to predict location/season specific module performance ratios.

The crystallisation of sputter-deposited, amorphous In2O3:H films was investigated. The influence of deposition and crystallisation parameters onto crystallinity and electron hall mobility was explored. Significant precipitation of metallic indium was discovered in the crystallised films by electron energy loss spectroscopy. Melting of metallic indium at ~160 &deg, C was suggested to promote primary crystallisation of the amorphous In2O3:H films. The presence of hydroxyl was ascribed to be responsible for the recrystallization and grain growth accompanying the inter-grain In-O-In bounding. Metallic indium was suggested to provide an excess of free electrons in as-deposited In2O3 and In2O3:H films. According to the ultraviolet photoelectron spectroscopy, the work function of In2O3:H increased during crystallisation from 4 eV to 4.4 eV, which corresponds to the oxidation process. Furthermore, transparency simultaneously increased in the infraredspectral region. Water was queried to oxidise metallic indium in UHV at higher temperature as compared to oxygen in ambient air. Secondary ion mass-spectroscopy results revealed that the former process takes place mostly within the top ~50 nm. The optical band gap of In2O3:H increased by about 0.2 eV during annealing, indicating a doping effect. This was considered as a likely intra-grain phenomenon caused by both (In0)O&bull, &bull, and (OH&minus, )O&bull, point defects. The inconsistencies in understanding of In2O3:H crystallisation, which existed in the literature so far, were considered and explained by the multiplicity and disequilibrium of the processes running simultaneously.