In this contribution we are analyzing and comparing the impact of two different alkali-fluorine post deposition treatments (KF and RbF) on the growth of chemical-bath-deposited CdS buffer layers on ...Cu(In,Ga)Se2 absorber layers for thin film solar cells. By combining Raman scattering, scanning electron microscopy, current-voltage analysis and measurements of the internal quantum efficiency we provide a comprehensive picture of this issue on the material and device level. We find that both PDTs lead to a better CdS-coverage of the surface of the CIGS, which leads to an improved junction quality at early growth stages compared to untreated devices. Furthermore the growth rate of the CdS is enhanced on KF-treated absorber layers while it is decreased on those treated with RbF (compared to the reference). This leads to a more stable behavior of RbF-treated devices after longer duration of the CdS deposition, while the KF-treated devices suffer from reduced fill factor and open circuit voltage. Furthermore we show that not only both PDTs but also the growth of the CdS lead to a reduction of the amount of the so called ordered defect compound, which is initially present at the surface of our absorber layers. This behavior indicates either the formation of CdCu -anti-sites or of a secondary phase at the interface.
•The effects of KF- and RbF-PDTs on the CIGS′ surface morphology are compared.•Both PDTs lead to a reduction of the Cu-poor phase at the surface of the CIGS.•An additional consumption of this phase is detected.•Both PDTs show an improved coverage of the surface of the CIGS by CdS.•The optimal CdS growth duration is found to be dependent on the PDT utilized.
The rapid rise of perovskite solar cells (PSCs) is increasingly limited by the available charge-selective contacts. This work introduces two new hole-selective contacts for p-i-n PSCs that outperform ...all typical p-contacts in versatility, scalability and PSC power-conversion efficiency (PCE). The molecules are based on carbazole bodies with phosphonic acid anchoring groups and can form self-assembled monolayers (SAMs) on various oxides. Besides minimal material consumption and parasitic absorption, the self-assembly process enables conformal coverage of arbitrarily formed oxide surfaces with simple process control. The SAMs are designed to create an energetically aligned interface to the perovskite absorber without non-radiative losses. For three different perovskite compositions, one of which is prepared by co-evaporation, we show dopant-, additive- and interlayer-free PSCs with stabilized PCEs of up to 21.1%. Further, the conformal coverage allows to realize a monolithic CIGSe/perovskite tandem solar cell with as-deposited, rough CIGSe surface and certified efficiency of 23.26% on an active area of 1 cm
2
. The simplicity and diverse substrate compatibility of the SAMs might help to further progress perovskite photovoltaics towards a low-cost, widely adopted solar technology.
We introduce new hole-selective contacts for next-generation perovskite photovoltaics and point to design paths for molecular engineering of perfect interfaces.
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.
Objective:Hyperactivity in frontal-striatal circuits is assumed to be involved in the pathophysiology of obsessive-compulsive disorder (OCD). In line with that, electrocortical correlates of ...overactive performance monitoring have been found to be associated with OCD independent from symptom state. The purpose of the present study was to elucidate whether overactive performance monitoring may represent a candidate endophenotype for OCD. In this case, unaffected first-degree relatives of OCD patients should also show this trait.
Method:Amplitudes of the error-related negativity and the correct-related negativity in the event-related brain potential during a flanker task were used to assess performance monitoring in three carefully matched groups: 30 patients with OCD, 30 unaffected first-degree relatives of OCD patients, and 30 healthy comparison subjects.
Results:Relative to the healthy comparison subjects, both unaffected first-degree relatives and OCD patients showed increased error-related brain potentials. No significant correlation was obtained between amplitudes and symptom severity measures, neither in patients nor in first-degree relatives.
Conclusions:Increased error-related brain potentials were observed not only in OCD patients but also in unaffected first-degree relatives. Overactive error monitoring may reflect a trait marker for OCD that is independent of the presence of clinical symptoms. Thus, enhanced error-related brain activity represents a candidate neurocognitive endophenotype for OCD.
IMPORTANCE Neurobiological models of obsessive-compulsive disorder (OCD) predict hyperactivity in brain circuits involving the orbitofrontal cortex and the basal ganglia, but it is unclear whether ...these areas are also characterized by altered brain network properties. OBJECTIVES To determine regions of abnormal degree connectivity in patients with OCD and to investigate whether connectivity measures are affected by antidepressant medication in OCD. DESIGN Case-control cross-sectional study using resting-state functional magnetic resonance imaging and a data-driven, model-free method to test for alterations in the degree of whole-brain, distant, and local connectivity in unmedicated patients with OCD compared with healthy controls. SETTING Outpatient clinic for OCD. PARTICIPANTS Twenty-three patients with OCD (12 women, 11 men) receiving no medication, 23 patients with OCD (14 women, 9 men) treated with antidepressant medication, and 2 equally sized control samples matched for age, sex, handedness, educational level, and IQ. MAIN OUTCOME MEASURES Statistical parametric maps testing the degree of distant and local functional connectivity of each voxel (hub analysis at voxel level) and OCD symptom severity. RESULTS Unmedicated patients with OCD showed greater distant connectivity in the orbitofrontal cortex and subthalamic nucleus and greater local connectivity in the orbitofrontal cortex and the putamen. Furthermore, distant connectivity of the orbitofrontal cortex and the putamen positively correlated with global OCD symptom severity. Medicated patients with OCD showed reduced local connectivity of the ventral striatum compared with the unmedicated patients. CONCLUSIONS AND RELEVANCE Consistent with neurobiological models of OCD, the orbitofrontal cortex and the basal ganglia are hyperconnected in unmedicated patients. The finding of distant connectivity alterations of the orbitofrontal cortex and the basal ganglia represents initial evidence of greater connections with distant cortical areas outside of corticostriatal circuitry. Furthermore, these data suggest that antidepressant medication may reduce connectivity within corticobasal ganglia-thalamo-cortical circuits in OCD.
In this contribution, the effectiveness of an RbF post deposition treatment (PDT) is evaluated in dependence on the Cu content of the absorber layer of Cu(In,Ga)Se 2 solar cells. It is shown that the ...PDT only acts beneficially on the open-circuit voltage and fill factor (FF) on samples with rather high Cu content, while it deteriorates all parameters of the solar cells in samples with low Cu content. In order to clarify the behavior of the open-circuit voltage, the well-known exchange mechanism of Rb and Na during the PDT is analyzed as a function of the Cu content of the absorber layers and discussed in regard to theoretical publications. Furthermore, a model explaining the observed effect on the FF based on the formation of an RbInSe 2 (RIS) layer during the RbF-PDT is proposed. The model supposes that the RIS layer acts as a barrier for the photocurrent and therefore lowers the FF. It is evaluated theoretically in dependence of the properties of the RIS layer using one-dimensional solar cell capacitance simulator (SCAPS) simulations. Finally, the proposed model is also tested and confirmed experimentally by directly depositing RIS onto untreated Cu(In,Ga)Se 2 layers.
We demonstrate a monolithic perovskite/CIGS tandem solar cell with a certified power conversion efficiency (PCE) of 24.2%. The tandem solar cell still exhibits photocurrent mismatch between the ...subcells; thus optical simulations are used to determine the optimal device stack. Results reveal a high optical potential with the optimized device reaching a short-circuit current density of 19.9 mA cm–2 and 32% PCE based on semiempirical material properties. To evaluate its energy yield, we first determine the CIGS temperature coefficient, which is at −0.38% K–1 notably higher than the one from the perovskite subcell (−0.22% K–1), favoring perovskite in the field operation at elevated cell temperatures. Both single-junction cells, however, are significantly outperformed by the combined tandem device. The enhancement in energy output is more than 50% in the case of CIGS single-junction device. The results demonstrate the high potential of perovskite/CIGS tandem solar cells, for which we describe optical guidelines toward 30% PCE.
Ambient-pressure Kelvin probe and photoelectron yield spectroscopy methods were employed to investigate the impact of the KF and RbF postdeposition treatments (KF-PDT, RbF-PDT) on the electronic ...features of Cu(In,Ga)Se
(CIGSe) thin films and the CdS/CIGSe interface in a CdS thickness series that has been sequentially prepared during the chemical bath deposition (CBD) process depending on the deposition time. We observe distinct features correlated to the CBD-CdS growth stages. In particular, we find that after an initial CBD etching stage, the valence band maximum (VBM) of the CIGSe surface is significantly shifted (by 180-620 mV) toward the Fermi level. However, VBM positions at the surface of the CIGSe are still much below the VBM of the CIGSe bulk. The CIGSe surface band gap is found to depend on the type of postdeposition treatment, showing values between 1.46 and 1.58 eV, characteristic for a copper-poor CIGSe surface composition. At the CdS/CIGSe interface, the lowest VBM discontinuity is observed for the RbF-PDT sample. At this interface, a thin layer with a graded band gap is found. We also find that K and Rb act as compensating acceptors in the CdS layer. Detailed energy band diagrams of the CdS/CIGSe heterostructures are proposed.
The performance of five hole‐transporting layers (HTLs) is investigated in both single‐junction perovskite and Cu(In, Ga)Se2 (CIGSe)‐perovskite tandem solar cells: nickel oxide (NiOx,), copper‐doped ...nickel oxide (NiOx:Cu), NiOx+SAM, NiOx:Cu+SAM, and SAM, where SAM is the 2‐(3,‐6Dimethoxy‐9H‐carbazol‐9yl)ethylphosphonic acid (MeO‐2PACz) self‐assembled monolayer. The performance of the devices is correlated to the charge‐carrier dynamics at the HTL/perovskite interface and the limiting factors of these HTLs are analyzed by performing time‐resolved and absolute photoluminescence ((Tr)PL), transient surface photovoltage (tr‐SPV), and X‐ray/UV photoemission spectroscopy (XPS/UPS) measurements on indium tin oxide (ITO)/HTL/perovskite and CIGSe/HTL/perovskite stacks. A high quasi‐Fermi level splitting to open‐circuit (QFLS‐Voc) deficit is detected for the NiOx‐based devices, attributed to electron trapping and poor hole extraction at the NiOx‐perovskite interface and a low carrier effective lifetime in the bulk of the perovskite. Simultaneously, doping the NiOx with 2% Cu and passivating its surface with MeO‐2PACz suppresses the electron trapping, enhances the holes extraction, reduces the non‐radiative interfacial recombination, and improves the band alignment. Due to this superior interfacial charge‐carrier dynamics, NiOx:Cu+SAM is found to be the most suitable HTL for the monolithic CIGSe‐perovskite tandem devices, enabling a power‐conversion efficiency (PCE) of 23.4%, Voc of 1.72V, and a fill factor (FF) of 71%, while the remaining four HTLs suffer from prominent Voc and FF losses.
Monolithic Cu(In,Ga)Se2 (CIGSe)‐perovskite tandem solar cells (23.4%‐efficient) manufactured on CIGSe absorbers with a non‐negligible surface roughness is demonstrated. Conformal coverage of the bottom sub‐cell, shunt prevention and high effective lifetime in the top cell, and fast hole extraction, favorable band alignment, and suppressed electron trapping at the HTL‐perovskite interface are achieved by using copper‐doped nickel oxide NiOx:Cu + 2‐(3,‐6Dimethoxy‐9H‐carbazol‐9yl)ethylphosphonic acid (MeO‐2PACz) as a hole‐transporting bi‐layer.
Monolithic Cs0.05(MA0.17FA0.83)0.95Pb(I0.83Br0.17)3/Cu(In,Ga)Se2 (perovskite/CIGS) tandem solar cells promise high performance and can be processed on flexible substrates, enabling cost-efficient and ...ultra-lightweight space photovoltaics with power-to-weight and power-to-cost ratios surpassing those of state-of-the-art III-V semiconductor-based multijunctions. However, to become a viable space technology, the full tandem stack must withstand the harsh radiation environments in space. Here, we design tailored operando and ex situ measurements to show that perovskite/CIGS cells retain over 85% of their initial efficiency even after 68 MeV proton irradiation at a dose of 2 × 1012 p+/cm2. We use photoluminescence microscopy to show that the local quasi-Fermi-level splitting of the perovskite top cell is unaffected. We identify that the efficiency losses arise primarily from increased recombination in the CIGS bottom cell and the nickel-oxide-based recombination contact. These results are corroborated by measurements of monolithic perovskite/silicon-heterojunction cells, which severely degrade to 1% of their initial efficiency due to radiation-induced recombination centers in silicon.
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•Halide perovskite sub-cells exhibit strong proton irradiation resiliency•Novel operando characterization distinguishes degradation of individual sub-cells•Perovskite/CIGS tandem solar cells retain 85% of their initial efficiency after irradiation•Perovskite/SHJ tandem solar cells degrade to 1% of their initial efficiency after irradiation
Monolithic perovskite/silicon and perovskite/CIGS tandem solar cells could facilitate large-scale decarbonization of the power sector, provided their long-term stability is proven. In this work, we test the stability of both technologies under high-energy proton irradiation. While this mimics the radiation environment in space, our versatile operando and ex situ methodology is also suitable for studying the long-term stability of multijunction solar cells for terrestrial applications. We find that perovskite/silicon tandem solar cells are unsuitable for space, whereas perovskite/CIGS tandems are radiation-hard, promising cheap, flexible, and ultra-lightweight space photovoltaics. Both the growing demand for smaller, cheaper satellites and the privatization of space exploration are revolutionizing space economics, providing an ideal niche for the commercialization of this new technology until the levelized cost-of-electricity can compete with current terrestrial photovoltaics.
We propose and test monolithic perovskite/CIGS tandem solar cells for readily stowable, ultra-lightweight space photovoltaics. We design operando and ex situ measurements to show that perovskite/CIGS tandem solar cells retain over 85% of their initial power-conversion efficiency after high-energy proton irradiation. While the perovskite sub-cell is unaffected after this bombardment, we identify increased non-radiative recombination in the CIGS bottom cell and nickel-oxide-based recombination layer. By contrast, monolithic perovskite/silicon-heterojunction cells degrade to 1% of their initial efficiency due to radiation-induced defects in silicon.
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