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
A new chemical route to Cu2ZnSn(SxSe1‐x)4 based thin film solar cells has been developed using spin coating of commercially available molecular precursors from an environmentally friendly non‐toxic ...solvent. 4.1% efficiency solar cells were achieved after selenization of Cu2ZnSnS4. This technique could provide simple, facile, and reproducible fabrication for efficient and large area solar cells.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
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
Organic–inorganic hybrid perovskite multijunction solar cells have immense potential to realize power conversion efficiencies (PCEs) beyond the Shockley–Queisser limit of single‐junction solar cells; ...however, they are limited by large nonideal photovoltage loss (V
oc,loss) in small‐ and large‐bandgap subcells. Here, an integrated approach is utilized to improve the V
oc of subcells with optimized bandgaps and fabricate perovskite–perovskite tandem solar cells with small V
oc,loss. A fullerene variant, Indene‐C60 bis‐adduct, is used to achieve optimized interfacial contact in a small‐bandgap (≈1.2 eV) subcell, which facilitates higher quasi‐Fermi level splitting, reduces nonradiative recombination, alleviates hysteresis instabilities, and improves V
oc to 0.84 V. Compositional engineering of large‐bandgap (≈1.8 eV) perovskite is employed to realize a subcell with a transparent top electrode and photostabilized V
oc of 1.22 V. The resultant monolithic perovskite–perovskite tandem solar cell shows a high V
oc of 1.98 V (approaching 80% of the theoretical limit) and a stabilized PCE of 18.5%. The significantly minimized nonideal V
oc,loss is better than state‐of‐the‐art silicon–perovskite tandem solar cells, which highlights the prospects of using perovskite–perovskite tandems for solar‐energy generation. It also unlocks opportunities for solar water splitting using hybrid perovskites with solar‐to‐hydrogen efficiencies beyond 15%.
High open‐circuit voltage, V
oc (1.98 V) and power conversion efficiency, PCE (18.5%) is realized in an ideal bandgap‐matched two‐terminal perovskite–perovskite tandem solar cell via an integrated approach. A fullerene variant, Indene‐C60 bis‐adduct is used to achieve optimized interfacial contact and alleviate hysteresis instabilities in the small‐bandgap subcell. Compositional engineering is employed to realize more highly photostabilized V
oc in the large‐bandgap subcell.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
We measure the room-temperature electron and hole field-effect mobilities (μFE) of a series of alkanedithiol-treated PbSe nanocrystal (NC) films as a function of NC size and the length of the alkane ...chain. We find that carrier mobilities decrease exponentially with increasing ligand length according to the scaling parameter β = 1.08−1.10 Å−1, as expected for hopping transport in granular conductors with alkane tunnel barriers. An electronic coupling energy as large as 8 meV is calculated from the mobility data. Mobilities increase by 1−2 orders of magnitude with increasing NC diameter (up to 0.07 and 0.03 cm2 V−1 s−1 for electrons and holes, respectively); the electron mobility peaks at a NC size of ∼6 nm and then decreases for larger NCs, whereas the hole mobility shows a monotonic increase. The size-mobility trends seem to be driven primarily by the smaller number of hops required for transport through arrays of larger NCs but may also reflect a systematic decrease in the depth of trap states with decreasing NC band gap. We find that carrier mobility is independent of the polydispersity of the NC samples, which can be understood if percolation networks of the larger-diameter, smaller-band-gap NCs carry most of the current in these NC solids. Our results establish a baseline for mobility trends in PbSe NC solids, with implications for fabricating high-mobility NC-based optoelectronic devices.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
The development of stable high-bandgap hybrid perovskites (HPs) with high optoelectronic quality may enable tandem solar cells with power conversion efficiencies approaching 30%. The halide ...composition of HPs has been observed to effect bandgap, carrier lifetime, and material stability. Here we report optoelectronic quality and stability under illumination of thousands of compositions ranging from the pure iodide (CH3NH3PbI3) to the diiodomonobromide (CH3NH3PbI2Br). Hyperspectral maps of steady-state absolute intensity photoluminescence (AIPL) are used to determine the quasi-Fermi level splitting (QFLS) at each point after synthesis. The QFLS upon first illumination increases with bandgap and reaches a maximum of 1.27 eV under 1 sun illumination intensity for a bandgap of 1.75 eV. However, the optoelectronic quality (χ), defined as the ratio of the QFLS to the maximum theoretical QFLS for bandgap, decreases with bandgap from around 88% for 1.60 eV bandgap down to 82% for 1.84 eV bandgap. Further, we show that a reversible light induced defect forms that reduces the optoelectronic quality, particularly for high-bandgap materials. Composition analysis shows that the halide to lead ratio, (I + Br)/Pb, decreases from 3 for the pure iodide to 2.5 for the diiodomonobromide, suggesting a role of halide vacancies or halide substitution defects in the light-induced instability for this synthesis route. Even with the light-induced defect, a stable QFLS of about 1.17 eV is possible. Comparing our QFLS to V oc values from HP devices reported in the literature indicates that higher open circuit voltages are possible but may require optimization of band alignment. Further, the spectral shape of the PL emission is found to be more commensurate with Franz–Keldysh broadening from local electric fields or from a screened Thomas–Fermi density of states (as opposed to a joint density of states due to Urbach disorder).
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
The ability to reproducibly synthesize nanocrystal (NC) inks with precisely controlled compositions is essential for making efficient kesterite solar cells from NCs. Here we present the results of a ...study on Cu–Zn–Sn–S NCs in which different particle size fractions were collected over a range of reaction times from various starting reagents. From this we have determined the temporal evolution of the NC ink and identified at least two distinct particle populations that form following injection: large particles containing primarily Cu and Zn, and small particles of Cu and Sn. For short reaction times, the extreme compositional heterogeneity between these size fractions makes the average ink composition highly sensitive to changes in reaction time and precipitation procedure. Longer synthesis times produce more consistent inks, with higher yield, and compositions closer to that of the starting reagents. The choice of metal precursor was found to have a minor impact on the composition of the resulting ink compared to the changes with time, even when substituting Ge precursors for Sn precursors. Using this understanding, we demonstrate the ability to produce inks with targeted off-stoichiometric compositions.
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
Reducing non-radiative recombination in semiconducting materials is a prerequisite for achieving the highest performance in light-emitting and photovoltaic applications. Here, we characterize both ...external and internal photoluminescence quantum efficiency and quasi-Fermi-level splitting of surface-treated hybrid perovskite (CH3NH3PbI3) thin films. With respect to the material bandgap, these passivated films exhibit the highest quasi-Fermi-level splitting measured to date, reaching 97.1 ± 0.7% of the radiative limit, approaching that of the highest performing GaAs solar cells. We confirm these values with independent measurements of internal photoluminescence quantum efficiency of 91.9 ± 2.7% under 1 Sun illumination intensity, setting a new benchmark for these materials. These results suggest hybrid perovskite solar cells are inherently capable of further increases in power conversion efficiency if surface passivation can be combined with optimized charge carrier selective interfaces.
Full text
Available for:
IZUM, KILJ, NUK, PILJ, PNG, SAZU, SBMB, UL, UM, UPUK
PDF
