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The use of carbazole‐based self‐assembled monolayer (SAM) as a hole transport layer (HTL) has led to the efficiency advancement in p–i–n perovskite solar cells (PSCs). However, PSCs with SAM HTL display a large spread in device performance even on small‐area substrates owing to poor SAM surface coverage and dewetting of the perovskite ink. Efforts to improve the uniformity in device performance of SAM‐based PSCs have been confined to spin‐coating method, which lacks high‐throughput capabilities and leads to excessive material wastage. Herein, a scalable bilayer HTL stack with sputtered NiO and blade‐coated SAM is utilized to achieve improved SAM coverage and accomplish uniform coating of perovskite absorber on 5 cm × 5 cm substrates. Fully scalable p–i–n PSCs with efficiency close to 19% with a minimal spread in device performance are achieved. To showcase the upscaling potential, near‐infrared‐transparent perovskite mini‐modules with efficiency close to 15% and 13% are achieved on an aperture area of 2.56 and 12.96 cm2. Together with low‐bandgap (1.0–1.1 eV) Cu(In,Ga)Se2 (CIGS) mini‐modules, the first fully scalable 4‐terminal perovskite‐CIGS tandem mini‐module with an efficiency of 20.5% and 16.9% on an aperture area of 2.03 and 10.23 cm2 is demonstrated. [ABSTRACT FROM AUTHOR]

Alkali treatments are crucial for low bandgap (Ag,Cu)InSe2 (ACIS) and Cu(In,Ga)Se2‐based solar cell performance. Traditionally, Ag‐alloying of CIS (ACIS) is grown on soda‐lime glass (SLG) at temperatures exceeding 500 °C, resulting in uncontrolled alkali diffusion from the substrate and variable photovoltaic properties. A substrate‐independent low‐bandgap ACIS growth process is introduced and the impact of controlled supplies of NaF and RbF alkali fluorides before and after absorber growth through precursor layers and post‐deposition treatments (PDT) are investigated. NaF and RbF precursor layers enhance carrier lifetimes and doping density, outperforming the previous SLG‐dependent strategy. Even small quantities of RbF significantly enhance device performance, while specific NaF amount during deposition are necessary to limit grain growth and achieve high doping densities and lifetimes. A certain density of grain boundaries appears crucial for high doping levels. Although subsequent NaF post‐deposition treatment (PDT) does not provide additional benefits with sufficient Na during growth, RbF‐PDT remains crucial. The best performance is achieved with a combination of NaF and RbF precursor layers along with RbF‐PDT, resulting in over 19% efficiency, 605 mV open‐circuit voltage (VOC), 73% fill factor (FF), a carrier density of 3 × 1016 cm−3, and a 700 ns lifetime. This approach supports high‐efficiency ACIS solar cell advancement, particularly for thin‐film tandem photovoltaic devices. [ABSTRACT FROM AUTHOR]

High efficiency chalcopyrite thin film solar cells generally use chemical bath deposited CdS as buffer layer. The transition to Cd-free buffer layers, ideally by dry deposition methods is required to decrease Cd waste, enable all vacuum processing and circumvent optical parasitic absorption losses. In this study, Zn1−xMgxO thin films were deposited by atomic layer deposition (ALD) as buffer layers on co-evaporated Cu(In,Ga)Se2 (CIGS) absorbers. A specific composition range was identified for a suitable conduction band alignment with the absorber surface. We elucidate the critical role of the CIGS surface preparation prior to the dry ALD process. Wet chemical surface treatments with potassium cyanide, ammonium hydroxide and thiourea prior to buffer layer deposition improved the device performances. Additional in-situ surface reducing treatments conducted immediately prior to Zn1−xMgxO deposition improved device performance and reproducibility. Devices were characterised by (temperature dependant) current-voltage and quantum efficiency measurements with and without light soaking treatment. The highest efficiency was measured to be 18%.

Photovoltaic conversion efficiency of CuInSe2 solar cells is limited by low fill factor (FF) and open‐circuit‐voltage (VOC) values compared to Si or perovskite solar cells. Herein, small quantities of Ag to alloy CuInSe2 to improve its properties are used, such as enhanced grain growth, higher crystal quality, and less detrimental defects, to overcome the device limitations of low‐bandgap CuInSe2 absorbers. The impact of Ag on the electronic properties of the bulk material and the buffer–absorber interface is examined at different stoichiometric compositions. Ag alloying improves the morphology with larger grain sizes, extends carrier lifetimes, and elevates net doping densities. Ag alloying reduces Cu‐depleted ordered‐vacancy compounds at the buffer–absorber interface and causes a chalcopyrite phase of high‐crystal‐quality independent of the I/III ratio. It is suggested Ag affects the formation of the alkali‐rich surface layer (Rb–In–Se). The best solar cell with an Ag‐alloyed CuInSe2 absorber achieves a VOC over 600 mV and FF values of about 74%, which result in a power conversion efficiency of 18.7% for low‐bandgap energy of 1.0 eV with short‐circuit current above 42 mA cm−2. The advantage of Ag alloying on the device performance of CuInSe2 solar cells will impact future applications in tandem devices. [ABSTRACT FROM AUTHOR]

Perovskite‐Cu(In,Ga)Se2 (CIGS) thin‐film tandem technology provides an exciting prospect to achieve low‐cost high‐efficiency photovoltaic devices by high throughput roll‐to‐roll processing on flexible substrates. However, no report on flexible perovskite‐CIGS mini‐modules has been published due to scribing‐related challenges in realizing near‐infrared (NIR)‐transparent perovskite mini‐modules on flexible substrates. Herein, an NIR‐transparent flexible perovskite mini‐module with an efficiency of 10.8% and an NIR‐transparency of over 75% is reported. All‐laser scribed interconnection approach is used to realize monolithic interconnection of mini‐modules on thermally sensitive soft flexible substrate. An analytical method is utilized to optimize the mini‐module layout and achieve a geometric fill factor of over 93%. Further, as a proof of concept, a flexible perovskite‐CIGS tandem mini‐module with an efficiency of 18.4% on an aperture area of 2.03 cm2 is demonstrated. To conclude, pathways for improving the efficiency of flexible NIR‐transparent perovskite mini‐modules are discussed. [ABSTRACT FROM AUTHOR]

Herein, the detrimental impact of radio frequency (RF)‐sputtering on bare Cu(In,Ga)Se2 photovoltaic absorbers in view of vacuum‐deposited buffer layers is evaluated, and the possible mitigation strategies are explored. Carrier lifetimes are measured using time‐resolved photoluminescence before and after buffer deposition and exposure to the plasma environment. When directly applied on bare Cu(In,Ga)Se2 absorbers, RF‐sputtering is severely limiting the device performance, with oxygen ions emanating from the target having a stronger effect than argon ions from the process gas. The possibilities to avoid sputter damage by atomic layer deposited Zn1−xMgxO and chemical bath deposited CdS buffer layers are shown, and the ability of the latter to restore damaged surfaces is highlighted. Absorber performance is also investigated for absorbers stored in air, N2, or ultra‐high vacuum. The reduction in carrier lifetime is reflected in the reduced open‐circuit voltage of solar cells. SCAPS simulations are used to investigate possibilities to minimize the effect of sputter damage. Finally, options on how to minimize sputter damage during buffer deposition as well as on how to modify the absorber to be less sensitive are discussed. [ABSTRACT FROM AUTHOR]

The power conversion efficiency of solar cells strongly depends on the open‐circuit voltage VOC which, in turn, depends on the recombination activity within the device. A possible source of detrimental charge carrier recombination is band tails. An empirical linear relationship between VOC loss and the Urbach energy of the band tails has been shown in the past. Here we discuss how band tails influence the radiative recombination and the nonradiative recombination in the bulk of the absorber. First, we show through photoluminescence that the band tails can be willfully tuned in state‐of‐the‐art thin‐film Cu (In,Ga)Se2 (CIGSe) absorbers and solar cells on a 20% efficiency level and beyond through the incorporation of alkali atoms. In the second part, we compare our CIGSe results to published results from other solar cell technologies. This comparison reveals that CIGS solar cells follow the previously described empirical trend: an increase in the open‐circuit voltage with decreasing band tails. Finally, we model the influence of tail states on the radiative and nonradiative recombination losses: Radiative recombination is increased because carriers thermalize into the tail states and nonradiative recombination of free carriers in the bands is increased because of Shockley–Read–Hall recombination through the tail states. The comparison with experimental data shows that the influence of tail states is even worse than the increase in radiative and SRH recombination predicted by our model. Our results thus suggest that band tails act as one of the main remaining voltage limitations in the majority of state‐of‐the‐art solar cells. [ABSTRACT FROM AUTHOR]

The open‐circuit voltage (VOC) is the main limitation to higher efficiencies of Cu(In,Ga)Se2 solar cells. One of the most critical parameters directly affecting VOC is the charge carrier lifetime. Therefore, it is essential to evaluate the extent to which inhomogeneities in material properties limit the carrier lifetime and how postdeposition treatments (PDTs) and growth conditions affect material properties. Time‐resolved photoluminescence (TRPL) microscopy is employed at conditions similar to one sun to study carrier lifetime fluctuations in Cu(In,Ga)Se2 with light (Na) and heavy (Rb) alkalis, different substrates, and grown at different temperatures. PDT lowers the amplitude of minority carrier lifetime fluctuations, especially for Rb‐treated samples. Upon PDT, the grains' carrier lifetime increases, and the analysis suggests a reduction in grain boundary recombination. Furthermore, lifetime fluctuations have a small impact on device performance, whereas VOC calculated from TRPL (and continuous‐wave PL) agrees with device values within the limits of investigated PDT samples. Finally, up to about half a per cent external radiative efficiencies are experimentally determined from TRPL metrics, and internal radiative efficiencies are approximated. The findings demonstrate that the highest absorber material quality investigated is still limited by nonradiative recombination (grain or grain boundary) and is comparable to state‐of‐the‐art absorbers. [ABSTRACT FROM AUTHOR]

Electronic transport in a semiconductor is key for the development of more efficient devices. In particular, the electronic transport parameters carrier lifetime and mobility are of paramount importance for the modeling, characterization, and development of new designs for solar cells and optoelectronic devices. Herein, time‐resolved photoluminescence mapping under low injection and wide‐field illumination conditions is used to measure the carrier lifetime and analyze the lateral charge carrier transport in Cu(In,Ga)Se2 absorbers grown at different temperatures, on different substrates, and subject to different postdeposition treatments (PDT) with light or heavy alkalis. To estimate the carrier mobility, numerical simulations of carrier diffusion transport to areas of increased recombination (defects) are used, similarly as observed experimentally. Mobilities are found in the range of 10–50 cm2 V−1 s−1, and effective minority carrier lifetime between 100 and 800 ns resulting in carrier diffusion lengths of 2–9 μm depending on the sample. Finally, the factors limiting carrier mobility and the implications of carrier diffusion on the measured carrier lifetimes are discussed. [ABSTRACT FROM AUTHOR]

Hydrogenated indium oxide (IOH) is implemented as transparent front contact in Cu(In,Ga)Se2 (CIGS) solar cells, leading to an open circuit voltage VOC enhanced by ~20mV as compared to reference devices with ZnO:Al (AZO) electrodes. This effect is reproducible in a wide range of contact sheet resistances corresponding to various IOH thicknesses. We present the detailed electrical characterization of glass/Mo/CIGS/CdS/intrinsic ZnO (i-ZnO)/transparent conductive oxide (TCO) with different IOH/AZO ratios in the front TCO contact in order to identify possible reasons for the enhanced VOC. Temperature and illumination intensity-dependent current-voltage measurements indicate that the dominant recombination path does not change when AZO is replaced by IOH, and it is mainly limited to recombination in the space charge region and at the junction interface of the solar cell. The main finding is that the introduction of even a 5 nm-thin IOH layer at the i-ZnO/TCO interface already results in a step-like increase in VOC. Two possible explanations are proposed and verified by one-dimensional simulations using the SCAPS software. First, a higher work function of IOH as compared to AZO is simulated to yield an VOC increase by 21 mV. Second, a lower defect density in the i-ZnO layer as a result of the reduced sputter damage during milder sputter-deposition of IOH can also add to a maximum enhanced VOC of 25 mV. Our results demonstrate that the proper choice of the front TCO contact can reduce the parasitic recombination and boost the efficiency of CIGS cells with improved corrosion stability. [ABSTRACT FROM AUTHOR]

High mobility hydrogenated indium oxide is investigated as a transparent contact for thin film Cu(In,Ga)Se2 (CIGS) solar cells. Hydrogen doping of In2O3 thin films is achieved by injection of H2O water vapor or H2 gas during the sputter process. As-deposited amorphous In2O3:H films exhibit a high electron mobility of ~50 cm²/Vs at room temperature. A bulk hydrogen concentration of ~4 at. % was measured for both optimized H2O and H2-processed films, although the H2O-derived film exhibits a doping gradient as detected by elastic recoil detection analysis. Amorphous IOH films are implemented as front contacts in CIGS based solar cells, and their performance is compared with the reference ZnO:Al electrodes. The most significant feature of IOH containing devices is an enhanced open circuit voltage (VOC) of ~20 mV regardless of the doping approach, whereas the short circuit current and fill factor remain the same for the H2O case or slightly decrease for H2. The overall power conversion efficiency is improved from 15.7% to 16.2% by substituting ZnO:Al with IOH (H2O) as front contacts. Finally, stability tests of non-encapsulated solar cells in dry air at 80 °C and constant illumination for 500 h demonstrate a higher stability for IOH-containing devices. [ABSTRACT FROM AUTHOR]

High efficiency chalcopyrite thin film solar cells generally use chemical bath deposited CdS as buffer layer. The transition to Cd-free buffer layers, ideally by dry deposition methods is required to decrease Cd waste, enable all vacuum processing and circumvent optical parasitic absorption losses. In this study, Zn1−xMgxO thin films were deposited by atomic layer deposition (ALD) as buffer layers on co-evaporated Cu(In,Ga)Se2 (CIGS) absorbers. A specific composition range was identified for a suitable conduction band alignment with the absorber surface. We elucidate the critical role of the CIGS surface preparation prior to the dry ALD process. Wet chemical surface treatments with potassium cyanide, ammonium hydroxide and thiourea prior to buffer layer deposition improved the device performances. Additional in-situ surface reducing treatments conducted immediately prior to Zn1−xMgxO deposition improved device performance and reproducibility. Devices were characterised by (temperature dependant) current-voltage and quantum efficiency measurements with and without light soaking treatment. The highest efficiency was measured to be 18%. [ABSTRACT FROM AUTHOR]

Cu(InGa)(SeS)2 films were deposited by thermal coevaporation of the elements at a substrate temperature of 550 °C with various [S]/[S+Se] and [Cu]/[In+Ga] ratios to investigate the preferred incorporation of S and Se under off-stoichiometric conditions. Deposition with a uniform flux-time profile under Cu-poor conditions, i.e., [Cu]/[In+Ga]<1, leads to preferential incorporation of Se relative to the vapor flux. With [Cu]/[In+Ga]>1, S is preferentially incorporated and, in this case, the resulting [S]/[Se+S] ratio in the film depends on the relative In and Ga concentrations. These results are compared to thermodynamic and kinetic models which both provide a functional form that can be used to predict the film composition from knowledge of the fluxes. Deposition processes, which use sequential layers of Cu-excess and Cu-poor growth, result in nonhomogeneous chalcogen composition. For Cu-poor followed by Cu-excess deposition, preferential incorporation of S occurs when the film reaches Cu-excess composition. For Cu-excess followed by Cu-free deposition, growth of Se-rich material is initiated while the film still contains excess Cu. Finally, a model of the film microstructure based on the incorporation of S and Se is discussed. [ABSTRACT FROM AUTHOR]

Cu(InGa)[(SeS).sub.2] (CIGSS) films are deposited by thermal coevaporation by using different uniform and sequential processes in order to examine the film formation and composition control under off-stoichiometry conditions. The deposition processes using sequential layers of Cu-excess and Cu-poor growth have resulted in nonhomogeneous chalcogen composition.