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Recently, metal halide perovskite-based top cells have shown significant potential for use in inexpensive and high-performance tandem solar cells. In state-of-the-art p-i-n perovskite/Si tandem devices, atomic-layer-deposited SnO2 has been widely used as a buffer layer in the top cells because it enables conformal, pinhole-free, and highly transparent buffer layer formation. In this work, the effects of various electrical properties of SnO2 and C60 layers on the carrier transport characteristics and the performance of the final devices were investigated using a numerical simulation method, which was established based on real experimental data to increase the validity of the model. It was found that the band alignment at the SnO2/C60 interface does, indeed, have a significant impact on the electron transport. In addition, as a general design rule, it was suggested that at first, the conduction band offset (CBO) between C60 and SnO2 should be chosen so as not to be too negative. However, even in a case in which this CBO condition is not met, we would still have the means to improve the electron transport characteristics by increasing the doping density of at least one of the two layers of C60 and/or SnO2, which would enhance the built-in potential across the perovskite layer and the electron extraction at the C60/SnO2 interface. [ABSTRACT FROM AUTHOR]

Conventional semi‐transparent perovskite solar cells (ST‐PSCs) generally exhibit inferior performance and stability relative to opaque PSCs. However, a comprehensive understanding of the origins of inferior performance and stability of ST‐PSCs and a practical solution to these challenges are both lacking. Here, it is shown for the first time that lithium ions from a lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)‐doped 2,2′,7,7′‐tetrakis[N,N‐di(4‐methoxyphenyl)amino]−9,9′‐spirobifluorene (Spiro‐MeOTAD) hole‐transport layer (HTL) can diffuse into the molybdenum trioxide buffer layer at their interface, yielding ST‐PSCs with lower efficiency and accelerated degradation. It is also demonstrated that this undesired Li‐ion diffusion can be avoided by HTL surface modification with stable lithium oxides. Using this approach, the constructed ST‐PSC exhibits a new record power conversion efficiency (PCE) of 22.02% (21.68% certified) and a fill factor of >80%, with >99% shelf‐stability after 400 h and >99% operational stability for 240 h, which clears away this longstanding limitation of the performance and stability of ST‐PSCs. This strategy is also applied to fabricate four‐ and two‐terminal perovskite/silicon tandem solar cells with bifacial equivalent efficiencies of 31.5% and 26.34%, respectively, at 20% albedo. [ABSTRACT FROM AUTHOR]

To accurately obtain an adjustable CdS layer, a quartz crystal microbalance (QCM) system is used in the chemical bath deposition (CBD) method by measuring the frequency change. However, although the thickness of the CdS layers deposited using the QCM system can be accurately adjusted to the same thickness, CdS layers of the same thickness formed in each section of the continuous reaction are expected to have different properties due to the reaction rate and mechanism, ultimately affecting the performance of solar cells. Therefore, 30 nm‐thick CdS layers are formed in the various reaction sections (initial, middle, and late ranges) and their characteristics and performances are examined and compared with the conventional 60 nm‐thick CdS buffer layer. Most Cu(In,Ga)Se2 (CIGS) solar cells with the 30 nm‐thick CdS buffer exhibit a higher efficiency than those with the 60 nm‐thick CdS buffer due to improved Jsc. However, the CIGS with the 30 nm CdS formed in the middle range exhibits the lowest photovoltaic performance. To investigate this unexpected result, all the deposited CdS layers are chemically, structurally, and optically examined and the results are explained by a deposition mechanism study. Furthermore, the effect of heat treatment is demonstrated by band alignment. [ABSTRACT FROM AUTHOR]

Abstract The structural, optical, and electrical properties of molybdenum (Mo) layers play a major role in Cu(In,Ga)Se 2 (CIGS) solar cell performance. The Mo layer works as a transport gate for diffusion of alkali ion from the soda-lime glass substrate to the back contact in CIGS solar cells. In the present work, Mo back contacts are controlled to exhibit two different orientations: (110)-oriented and randomly oriented. The influence of these orientations on CIGS absorbers and resulting solar cells is investigated. In situ thermo-Raman spectroscopy and secondary ion mass spectrometry results indicate that the greater amount of alkali ions are found in the CIGS absorber with randomly oriented Mo back contact than in the (110)-orientated Mo back contact. The resulting different Na incorporations significantly affect the performance of the resulting devices. Devices with the randomly oriented Mo back contact exhibit superior device performances to the devices with (110)-oriented Mo back contact. With comprehensive device characterizations, an alkali ion release determined by the orientation of the Mo back contact affects the recombination mechanism in the CIGS bulk and the back contact properties at the CIGS/Mo interface. Highlights • The crystal orientation of Mo greatly affects alkali incorporation into CIGS films. • Alkali incorporation by the orientation of Mo is dynamically observed via Thermo-Raman spectroscopy technique. • Alkali incorporation influences not only the CIGS bulk but also CIGS/Mo interface. • Correlation between device performance and alkali incorporation is discussed. [ABSTRACT FROM AUTHOR]

Novel Phenothiazine-Based Self-Assembled Monolayer as a Hole Selective Contact for Highly Efficient and Stable p-i-n Perovskite Solar Cells (Adv. Efficiency, hole transport layers, perovskite solar cells, self-assembled monolayers, stability Keywords: efficiency; hole transport layers; perovskite solar cells; self-assembled monolayers; stability EN efficiency hole transport layers perovskite solar cells self-assembled monolayers stability 1 1 1 01/18/22 20220113 NES 220113 B Perovskite Solar Cells b In article number 2103175, Young S. Park, Sungjun Hong and co-workers design a halogenated phenothiazine based self-assembled monolayer as a new type of hole transporting layer in inverted perovskite solar cells, displaying an energetically well aligned interface with the light absorbing perovskite top layer. [Extracted from the article]

Graphical abstract Highlights • Semi-transparent CIGS solar cells are deposited on FTO substrates by single stage co-evaporation. • Optimal Na content in the absorber layer is critical for solar cell performance. • 6.46% PCE and 18.59% AVT for the solar cell with 200-nm-thick absorber is obtained. Abstract Semi-transparent thin-film solar cells with ultra-thin Cu(In,Ga)Se 2 (CIGS) absorber layers were fabricated on fluorine-doped tin oxide coated glass substrates using a single-stage co-evaporation process. The effects of the deposition conditions, such as the absorber thickness, deposition temperature, and post-deposition treatment using NaF on the material properties of the CIGS films were evaluated. In addition, the power conversion efficiency (PCE) and average visible transmission (AVT) in the wavelength range of 420–720 nm for semi-transparent CIGS solar cells using these absorber layers were systematically investigated. The AVT of the solar cells was directly dependent on the thickness of the CIGS absorber films. When the film thickness of the absorber layers increased from 300 nm to 950 nm, the AVT decreased gradually from 9.04% to 0.30%, while their PCE values did not show a clear dependence on the absorber thickness. Narrow columnar grains were observed in the microstructure of the ultra-thin CIGS absorber layers, irrespective of the film thickness and deposition temperature. Doping the ultra-thin CIGS absorber layers with Na after film deposition enhanced solar cell performance (the open circuit voltage (V OC) and fill factor (FF) were improved). The enhanced cell performance was attributed to the lack of a resistive GaO x film at the CIGS/FTO interface and thermal damage to the FTO back contact. The PCE values of semi-transparent solar cells with ultra-thin CIGS absorber layers prepared under the optimal deposition conditions varied from 6.46% to 9.78% when the CIGS absorber thickness was varied from 200 nm to 300 nm, respectively, while the corresponding AVT values changed from 18.59% to 9.04%. [ABSTRACT FROM AUTHOR]

• A facile organic halide post-treatment for triple-halide wide-bandgap perovskite was proposed. • Concurrent diffusion of organic halide salt results in reconstruction of perovskite film. • The reconstructed perovskite exhibits suppressed nonradiative recombination and reduced Urbach energy. • Four-terminal perovskite/Cu(In,Ga)Se 2 tandem cells achieve a power conversion efficiency of 24.5%. Wide-bandgap (E g) perovskites (PVSK) are important materials for realizing high-efficiency tandem devices that surpass the efficiency limit of single-junction solar cells. However, they suffer from phase separation and open-circuit voltage (V oc) loss. This study demonstrated a facile fabrication strategy of highly efficient and stable wide- E g PVSKs through an organic halide surface treatment with formamidinium bromide to CH 3 NH 3 PbI 3-x Cl x. The concurrent diffusion of organic cations and halide ions from the surface into bulk PVSK results in the complete conversion of the PVSK crystallinity to a cubic phase, eliminating segregated secondary phases and reducing unreacted PbI 2. Br incorporation induces halide redistribution, resulting in the formation of triple-halide wide- E g PVSK. The complete reconstruction of the bulk and surface of PVSK by surface post-treatment suppresses trap-induced nonradiative recombination and decreases the Urbach tail energy. Inverted PVSK solar cells based on the reconstructed PVSK exhibit enhanced photovoltaic performance with a low V oc deficit and high stability. In addition, we demonstrated a four-terminal (4-T) tandem device based on the triple-halide wide- E g PVSK as a top cell combining with a Cu(In,Ga)Se 2 bottom cell, achieving a power conversion efficiency of 24.5 %. [ABSTRACT FROM AUTHOR]

• Se@Ag 2 Se core-shells were added as Ag precursors to hybrid inks for the fabrication of low-cost, non-toxic ACIGS thin films. • The hybrid ink was readily prepared by bulk synthesis of Se@Ag 2 Se core-shells, which improved upon conventional synthesis conditions. • The Se@Ag 2 Se core-shell not only allows the Ag 2 Se on the surface to be used as an Ag precursor, but also reduces the process temperature for thin film formation due to the low melting point (221 °C) of the amorphous Se in the core. • ACIGS thin films were formed at 347 °C with a hybrid ink containing a Se@Ag 2 Se core-shell. • Sb was doped into the thin film to optimize the formed ACIGS thin films, and their solar cells were fabricated and characterized. To create (Ag,Cu)(In,Ga)Se 2 (ACIGS) thin films using a hybrid ink method, large-scale synthesis of Se@Ag 2 Se core-shell and Cu-Se nanoparticles was performed, surpassing the scale of previous methods. In particular, although the Se@Ag 2 Se core-shell was also a precursor for Ag in ACIGS, the amorphous Se (a -Se) in the Se@Ag 2 Se core-shell acted as a flux during the reaction due to its low melting temperature (221 °C), resulting in the formation of ACIGS thin films at a lower reaction temperature (∼340 °C) and shorter reaction time (30 min) than conventional ones (∼530 °C, 60 min). Furthermore, by varying the amount of Se@Ag 2 Se core-shell in the hybrid ink, the Ag ratio (Ag/(Ag + Cu)) was controlled, and pure ACIGS without secondary phases was obtained. However, the ACIGS solar cells fabricated by this method had a conversion efficiency of only approximately 4% and relatively low shunt resistance (R sh) and carrier concentration (∼1015/cm3). To improve the R sh and carrier concentration, ACIGS was doped with Sb by mixing the Sb precursor into the hybrid ink. The Sb-doped ACIGS exhibited grain growth and grain boundary reduction without secondary phase formation. In addition, capacitance–voltage (C–V) measurements showed an increase in the carrier concentration (∼1016/cm3). Therefore, the conversion efficiency of Sb-doped ACIGS increased with increasing R sh and open-circuit voltage (V OC). [ABSTRACT FROM AUTHOR]

• Small amounts of Ag were incorporated into three-stage co-evaporated CIGS solar cells. • Ag homogenization occurred and alkali profiles were affected. • Ag-alloyed CIGS solar cells exhibited superior performance relative to that of cells without Ag alloying. • Ag alloying resulted in an increased charge density and a reduced detrimental state density. [Display omitted] In this work, to improve the performance of three-stage co-evaporated Cu(In,Ga)Se 2 (CIGS) solar cells, a small amount of Ag was incorporated during the third stage, and the materials/device characteristics were investigated. Although the amount of added Ag was limited to less than 1 at%, both the film microstructure and the resulting device performance were affected. The Ag-alloyed CIGS thin films exhibited enhanced recrystallization and homogenous Ag distribution throughout the CIGS film bulk, even though the Ag incorporation was performed near the end of the three-stage co-evaporation process. Well-controlled Ag alloying into CIGS solar cells (approximately 0.6 at%) led to increased fill factors, accompanied by increased charge carrier densities as well as reduced detrimental state densities. The approach performed in the present work suggests that the device quality of CIGS solar cells can be tuned by small Ag additions in a similar manner to extrinsic alkali incorporation. [ABSTRACT FROM AUTHOR]