Cu2ZnSnS4 (CZTS) and Cu2ZnSnSe4 (CZTSe) based solar cells are promising candidates for low cost solar cells due to the natural abundance and low toxicity of the constituent elements. Here, we present ...the first reported synthesis of colloidal CZTS nanocrystals using a simple solution-phase method. Solar cells fabricated using selenized CZTS nanocrystal inks had a power conversion efficiency of 0.74% under AM1.5G illumination.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
Cu2Zn(Sn1− x Ge x )S4 nanocrystals have been synthesized via batch reaction in oleylamine with no additional surfactants present. The nanocrystals are knife-coated on molybdenum substrates and then ...selenized to form a dense layer of Cu2Zn(Sn1− x Ge x )(S,Se)4, which is then used as the photoabsorbing layer in a thin film solar cell. The band gaps of the nanocrystals and the resulting solar cells are demonstrated to be controlled by adjusting the Ge/(Ge+Sn) ratio of the nanocrystal synthesis precursors. Solar cells fabricated from Cu2ZnGeS4 nanocrystal films yielded a power conversion efficiency of 0.51%. However, Cu2Zn(Snx Ge 1− x )S4 nanocrystals with a Ge/(Ge+Sn) ratio 0.7 yielded devices with an efficiency of 6.8% when synthesized to be Cu-poor and Zn-rich. This result opens the possibility of forming Ge gradients to direct minority carriers away from high recombination interfaces and significantly improve the device efficiency of CZTSSe-based solar cells.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
Earth abundant copper-zinc-tin-chalcogenide (CZTSSe) is an important class of material for the development of low cost and sustainable thin film solar cells. The fabrication of CZTSSe solar cells by ...selenization of CZTS nanocrystals is presented. By tuning the composition of the CZTS nanocrystals and developing a robust film coating method, a total area efficiency as high as 7.2% under AM 1.5 illumination and light soaking has been achieved.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
Current biomass utilization processes do not make use of lignin beyond its heat value. Here we report on a bimetallic Zn/Pd/C catalyst that converts lignin in intact lignocellulosic biomass directly ...into two methoxyphenol products, leaving behind the carbohydrates as a solid residue. Genetically modified poplar enhanced in syringyl (S) monomer content yields only a single product, dihydroeugenol. Lignin-derived methoxyphenols can be deoxygenated further to propylcyclohexane. The leftover carbohydrate residue is hydrolyzed by cellulases to give glucose in 95% yield, which is comparable to lignin-free cellulose (solka floc). New conversion pathways to useful fuels and chemicals are proposed based on the efficient conversion of lignin into intact hydrocarbons.
Large-grain absorber formation through selenization techniques is a promising route for high performance chalcogenide solar cells. Understanding and subsequently controlling such grain growth is ...essential in improving absorber quality and developing absorbers with unique optoelectronic and morphological properties. We explain the essential role of liquid selenium in the grain growth of Cu2ZnSnSe4 (CZTSe) absorbers from Cu2ZnSnS4 nanoparticles by proposing a liquid-assisted grain growth mechanism. Through the use of a multizone rapid-thermal-processing furnace, control of liquid Se delivery to the film and the Se(g) atmosphere during processing is shown to result in novel absorbers with tunable properties. Additionally, the processing parameters necessary for high quality CZTSe absorbers, the role of nanoparticle properties, and the role of alkali metal dopants in the liquid-assisted growth mechanism are shown. Ultimately, record nanoparticle-based device performance of 9.3% is achieved for selenized CZTSe absorbers.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
Time‐resolved photoluminescence (TRPL) is a powerful characterization technique to study carrier dynamics and quantify absorber quality in semiconductors. The minority carrier lifetime, which is ...critically important for high‐performance solar cells, is often derived from TRPL analysis. However, here it is shown that various nonideal absorber properties can dominate the TRPL signal making reliable extraction of the minority carrier lifetime not possible. Through high‐resolution intensity‐, temperature‐, voltage‐dependent, and spectrally resolved TRPL measurements on absorbers and devices it is shown that photoluminescence (PL) decay times for kesterite materials are dominated by minority carrier detrapping. Therefore, PL decay times do not correspond to the minority carrier lifetime for these materials. The lifetimes measured here are on the order of hundreds of picoseconds in contrast to the nanosecond lifetimes suggested by the decay curves. These results are supported with additional measurements, device simulation, and comparison with recombination limited PL decays measured on Cu(In,Ga)Se2. The kesterite material system is used as a case study to demonstrate the general analysis of TRPL data in the limit of various measurement conditions and nonideal absorber properties. The data indicate that the current bottleneck for kesterite solar cells is the minority carrier lifetime.
Minority carrier lifetimes are often overestimated for kesterite materials from time‐resolved photoluminescence (TRPL) due to complex charge carrier dynamics in this material system. Here, it is shown that detrapping processes dominate the photoluminescence decay for Cu2ZnSnSe4 and Cu2ZnSn(S,Se)4. Minority carrier lifetimes ≤500 ps are estimated from TRPL, device simulation, and additional measurements demonstrating a significant performance limitation.
Full text
Available for:
FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
PDF
