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26th European Photovoltaic Solar Energy Conference and Exhibition; 65-68, Transition-metal doped chalcopyrite thin films have been proposed as a suitable absorber material for intermediate band solar cells. In this work CuGa1-xFexS2 thin films were grown by vacuum coevaporation at a substrate temperature of 400°C with various amounts of Fe incorporated. The optical response of thin films grown on soda-lime glass was evaluated by transmittance/reflectance measurements. Photovoltaic devices were fabricated from CuGa1-xFexS2 thin films concurrently deposited on Mo-coated glass substrates using the standard chalcopyrite glass/Mo/absorber/CdS/ZnO device structure. The device characteristics of these solar cells were evaluated by current-voltage and quantum efficiency measurements. For Fe-containing CuGaS2 films distinct subgap absorption bands at 1.2 eV and 1.9 eV are detected, which increase in prominence with increasing Fe content. On the other hand, the solar cell parameters were found to deteriorate with increasing iron content indicating an increase in nonradiative recombination when high levels of iron are incorporated. However, for the lowest iron content (x=0.003) an increase in the subgap photoresponse at about 1.9 eV is observed which is attributed to a combination of sufficient intermediate band absorption and carrier collection at this dilution level.

Through the optimization of the perovskite precursor composition and interfaces to selective contacts, we achieved a p i n type perovskite solar cell PSC with a 22.3 power conversion efficiency PCE . This is a new performance record for a PSC with an absorber bandgap of 1.63 eV. We demonstrate that the high device performance originates from a synergy between 1 an improved perovskite absorber quality when introducing formamidinium chloride FACl as an additive in the triple cation Cs0.05FA0.79MA0.16PbBr0.51I2.49 Cs MAFA perovskite precursor ink, 2 an increased open circuit voltage, VOC, due to reduced recombination losses when using a lithium fluoride LiF interfacial buffer layer, and 3 high quality hole selective contacts with a self assembled monolayer SAM of [2 9H carbazol 9 yl ethyl]phosphonic acid 2PACz on ITO electrodes. While all devices exhibit a high performance after fabrication, as determined from current density voltage, J V, measurements, substantial differences in device performance become apparent when considering longer term stability data. A reduced long term stability of devices with the introduction of a LiF interlayer is compensated for by using FACl as an additive in the metal halide perovskite thin film deposition. Optimized devices maintained about 80 of the initial average PCE during maximum power point MPP tracking for gt;700 h. We scaled the optimized device architecture to larger areas and achieved fully laser patterned series interconnected mini modules with a PCE of 19.4 for a 2.2 cm2 active area. A robust device architecture and reproducible deposition methods are fundamental for high performance and stable large area single junction and tandem modules based on PSCs

Recent advancements in perovskite solar cell performance were achieved by stabilizing the α-phase of FAPbI3 in nip-type architectures. However, these advancements could not be directly translated to pin-type devices. Here, we fabricated a high-quality double cation perovskite (MA0.07FA0.93PbI3) with low bandgap energy (1.54 eV) using a two-step approach on a standard polymer (PTAA). The perovskite films exhibit large grains (∼1 μm), high external photoluminescence quantum yields of 20%, and outstanding Shockley-Read-Hall carrier lifetimes of 18.2 μs without further passivation. The exceptional optoelectronic quality of the neat material was translated into efficient pin-type cells (up to 22.5%) with improved stability under illumination. The low-gap cells stand out by their high fill factor (∼83%) due to reduced charge transport losses and short-circuit currents >24 mA cm-2. Using intensity-dependent quasi-Fermi level splitting measurements, we quantify an implied efficiency of 28.4% in the neat material, which can be realized by minimizing interfacial recombination and optical losses.

Halide perovskites are a strong candidate for the next generation of photovoltaics. Chemical doping of halide perovskites is an established strategy to prepare the highest efficiency and most stable perovskite-based solar cells. In this study, we unveil the doping mechanism of halide perovskites using a series of alkaline earth metals. We find that low doping levels enable the incorporation of the dopant within the perovskite lattice, whereas high doping concentrations induce surface segregation. The threshold from low to high doping regime correlates to the size of the doping element. We show that the low doping regime results in a more n-type material, while the high doping regime induces a less n-type doping character. Our work provides a comprehensive picture of the unique doping mechanism of halide perovskites, which differs from classical semiconductors. We proved the effectiveness of the low doping regime for the first time, demonstrating highly efficient methylammonium lead iodide based solar cells in both n-i-p and p-i-n architectures.

We have developed a new noninvasive optical method for monitoring charge carrier diffusion and mobility in semiconductor thin films in the direction perpendicular to the surface which is most relevant for devices. The method is based on standard transient absorption measurements carried out in reflectance and transmittance modes at wavelengths below the band gap where the transient response is mainly determined by the change in refractive index, which in turn depends on the distribution of photogenerated carriers across the film. This distribution is initially inhomogeneous because of absorption at the excitation wavelength and becomes uniform over time via diffusion. By modeling these phenomena we can determine the diffusion constant and respective mobility. Applying the method to a 500 nm thick triple cation FAMACs perovskite film revealed that homogeneous carrier distribution is established in few hundred picoseconds, which is consistent with mobility of 66 cm2 (V s)-1. publishedVersion

Efficiency from hole-selective contacts Perovskite/silicon tandem solar cells must stabilize a perovskite material with a wide bandgap and also maintain efficient charge carrier transport. Al-Ashouri et al. stabilized a perovskite with a 1.68–electron volt bandgap with a self-assembled monolayer that acted as an efficient hole-selective contact that minimizes nonradiative carrier recombination. In air without encapsulation, a tandem silicon cell retained 95% of its initial power conversion efficiency of 29% after 300 hours of operation. Science , this issue p. 1300