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Numerous phosphorus rich metal phosphides containing both P amp; 8722;P bonds and metal amp; 8722;P bonds are known from the solid state chemistry literature. A method to grow these materials in thin film form would be desirable, as thin films are required in many applications and they are an ideal platform for high throughput studies. In addition, the high density and smooth surfaces achievable in thin films are a significant advantage for characterization of transport and optical properties. Despite these benefits, there is hardly any published work on even the simplest binary phosphorus rich phosphide films. Here, we demonstrate growth of single phase CuP2 films by a two step process involving reactive sputtering of amorphous CuP2 x and rapid annealing in an inert atmosphere. At the crystallization temperature, CuP2 is thermodynamically unstable with respect to Cu3P and P4. However, CuP2 can be stabilized if the amorphous precursors are mixed on the atomic scale and are sufficiently close to the desired composition neither too P poor nor too P rich . Fast formation of polycrystalline CuP2, combined with a short annealing time, makes it possible to bypass the diffusion processes responsible for decomposition. We find that thin film CuP2 is a 1.5 eV band gap semiconductor with interesting properties, such as a high optical absorption coefficient above 105 cm amp; 8722;1 , low thermal conductivity 1.1 W K m , and composition insensitive electrical conductivity around 1 S cm . We anticipate that our processing route can be extended to other phosphorus rich phosphides that are still awaiting thin film synthesis and will lead to a more complete understanding of these materials and of their potential applications

The effect of Cu off stoichiometry and Zn alloying on the fundamental absorption region of Cu2CdSnS4 CCTS absorbers in complete solar cells has been investigated using electroreflectance ER spectroscopy at room temperature. It is found that ER spectra consist of contributions from two different sources, one of which corresponds to band gap transition in the absorber layer and the other to the interference effect in the window layer. ER measurements on CCTS samples reveal a near constant band gap energy of 1.37 1.38 eV and a relatively small broadening of 60 90 meV in the probed 0.8 lt;Cu Cd Sn lt;0.89 compositional range, in contrast to related kesterites Cu2ZnSn S,Se 4. The analysis of the band gap in Cu2 Cd1 amp; 8722;x,Znx SnS4 alloys yields a quadratic dependence on Zn content with a bowing parameter of 0.4 eV. Finally, the broadening parameters of the band gap transitions as well as their compositional dependence are evaluated and discussed

The effect of Cu off-stoichiometry and Zn alloying on the fundamental absorption region of (CCTS) absorbers in complete solar cells has been investigated using electroreflectance (ER) spectroscopy at room temperature. It is found that ER spectra consist of contributions from two different sources, one of which corresponds to band gap transition in the absorber layer and the other to the interference effect in the window layer. ER measurements on CCTS samples reveal a near-constant band gap energy of 1.37-1.38 eV and a relatively small broadening of 60-90 meV in the probed compositional range, in contrast to related kesterites . The analysis of the band gap in alloys yields a quadratic dependence on Zn content with a bowing parameter of 0.4 eV. Finally, the broadening parameters of the band gap transitions as well as their compositional dependence are evaluated and discussed. National Research Foundation (NRF) Published version L.H.W. and S.H. acknowledge the funding support from the CREATE Programme under the Campus for Research Excellence and Technological Enterprise (CREATE), which is supported by the National Research Foundation, Prime Minister’s Office, Singapore.

The performance of Cu2ZnSnSe4 solar cells is presently limited by low values of open circuit voltage which are a consequence of strong band tailing and high level of nonradiative recombination. Recently, the partial substitution of Cu, Zn, and Sn by other elements has shown the potential to overcome this limitation. We explored the structural changes and the effect on the optoelectronic properties of the partial substitution of Cu with Ag in Cu2ZnSnSe4. This paper clari amp; 64257;es the crystal structure of Ag1 amp; 8722;xCux 2ZnSnSe4 solid solution series, deducing possible cationic point defects and paying special attention to the presence of Cu Zn disorder with a combination of neutron and x ray diffraction. The optoelectronic properties of the solid solution series are assessed using re amp; 64258;ection and quantitative photoluminescence spectroscopy, which allows us to estimate the fraction of nonradiative recombination, which would contribute to the open circuit voltage loss in devices. The results strongly suggest Ag incorporation as a promising route to eliminate Cu Zn disorder and to reduce nonradiative recombination losses in Cu2ZnSnSe4.

Understanding the relationship of photoexcited carrier lifetimes, mobilities, and recombination mechanisms to structural properties and processing of photovoltaic PV absorber materials is critical to the design of efficient solar cells. Carrier dynamics in PV absorbers have conventionally been characterized by time resolved photoluminescence TRPL , but TRPL may not be suitable or straightforward for all absorbers. Alternative non contact methods can enable measurement of ultrafast carrier dynamics for a wider range of materials. Here we demonstrate the complementary use of time resolved terahertz spectroscopy TRTS and near infrared transient reflectance NIR TR spectroscopy along with TRPL to elucidate photoexcited carrier dynamics in a high quality copper poor, zinc rich kesterite Cu2ZnSnSe4 CZTSe single crystal. The single crystalline nature of the sample eliminates complications arising from grain boundaries, secondary phases, and interfaces associated with thin film growth. A single crystal based PV device exhibited an efficiency of 6.2 and Voc of 400 mV, consistent with the quasi Fermi level splitting determined using absolute photoluminescence. NIR TR showed picosecond scale cooling and relaxation of carriers into a distribution of band tail states while TRTS revealed a characteristic time scale of 200 260 ps for recombination. Hall effect and TRTS measurements revealed electron and hole mobilities in the range of 50 100 cm2 Vs and a majority carrier density of 9x1016 cm 3. These dynamics result in a characteristic minority carrier diffusion length of less than 200 nm, leading to incomplete carrier collection, as confirmed by a strongly decreasing external quantum efficiency at long wavelengths on a device prepared on the crystal. Our approach combining ultrafast spectroscopy and device measurements can lead to more detailed understanding of performance limiting photophysical processes and can subsequently accelerate the development of more efficient PVs

Determining elemental distributions dependent on the thickness of a sample is of utmost importance for process optimization in different fields e.g. from quality control in the steel industry to controlling doping profiles in semiconductor labs. Glow discharge optical emission spectrometry (GD-OES) is a widely used tool for fast measurements of depth profiles. In order to be able to draw profound conclusions from GD-OES profiles, one has to optimize the measurement conditions for the given application as well as to ensure the suitability of the used emission lines. Furthermore a quantification algorithm has to be implemented to convert the measured properties (intensity of the emission lines versus sputtering time) to more useful parameters, e.g. the molar fractions versus sample depth (depth profiles). In this contribution a typical optimization procedure of the sputtering parameters is adapted to the case of polycrystalline Cu(In,Ga)(S,Se)2 thin films, which are used as absorber layers in solar cell devices, for the first time. All emission lines used are shown to be suitable for the quantification of the depth profiles and a quantification routine based on the assumption of constant emission yield is used. The accuracy of this quantification method is demonstrated on the basis of several examples. The bandgap energy profile of the compound semiconductor, as determined by the elemental distributions, is compared to optical measurements. The depth profiles of Na-the main dopant in these compounds-are correlated with measurements of the open-circuit voltage of the corresponding devices, and the quantification of the sample depth is validated by comparison with profilometry and X-ray fluorescence measurements.

As the open circuit voltage in CZTSSe devices is believed to be limited by absorber band tailing caused by the exceptionally high density of Cu Zn disorder, replacing of Cu with Ag this density is predicted to drop. In this study, neutron diffraction and diffuse reflectance were applied to evaluate the crystal structure and optoelectronic properties of the Ag 1 x Cu x 2 ZnSnSe 4 solid solution ACZTSe . The results allow us to suggest that in spite of both end members of the solid solution being reported to crystallize in kesterite type structure, at least Ag 1 x Cu x 2 ZnSnSe4 with x 0.17 and 0.46 crystallize in the stannite type structure and thus block Cu Zn disorder