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Solution-processed ZnO is commonly used as a charge-selective interlayer between an absorber and electrode in organic solar cells. In this work, the impact of the resistance of the sol–gel grown ZnO interlayer on solar cell performance is investigated. We find that the UV-induced doping effect leads to a significantly reduced ZnO resistance, which gives rise to an underestimated photoactive area and thus overestimated short-circuit current density (Jsc) for the solar cell measured without an aperture. Moreover, we show that this so far mostly overlooked issue can be unintentionally triggered during common fabrication and characterization processes, because the UV photons flux from a solar simulator, or from a light source for encapsulating the solar cell, are already sufficient in leading to the too much increased lateral conductivity of the ZnO. Finally, we demonstrate that interlayers with rather high sheet resistance can lead to an overestimation of Jsc (e.g. by 10% for a 10 MΩ per square interlayer in a 2 mm2 device). Therefore, the validity of the argument that high-resistance interlayers do not lead to overestimated Jsc should always be carefully evaluated.

Despite the outstanding role of mesoscopic structures on the efficiency and stability of perovskite solar cells (PSCs) in the regular (n–i–p) architecture, mesoscopic PSCs in inverted (p–i–n) architecture have rarely been reported. Herein, an efficient and stable mesoscopic NiOx (mp-NiOx) scaffold formed via a simple and low-cost triblock copolymer template-assisted strategy is employed, and this mp-NiOx film is utilized as a hole transport layer (HTL) in PSCs, for the first time. Promisingly, this approach allows the fabrication of homogenous, crack-free, and robust 150 nm thick mp-NiOx HTLs through a facile chemical approach. Such a high-quality templated mp-NiOx structure promotes the growth of the perovskite film yielding better surface coverage and enlarged grains. These desired structural and morphological features effectively translate into improved charge extraction, accelerated charge transportation, and suppressed trap-assisted recombination. Ultimately, a considerable efficiency of 20.2% is achieved with negligible hysteresis which is among the highest efficiencies for mp-NiOx based inverted PSCs so far. Moreover, mesoscopic devices indicate higher long-term stability under ambient conditions compared to planar devices. Overall, these results may set new benchmarks in terms of performance for mesoscopic inverted PSCs employing templated mp-NiOx films as highly efficient, stable, and easy fabricated HTLs.

In the present explorative data analysis, for the first time possible, coherences were identified for interpersonal input and self-disclosure, - two factors which are highly important in the context of psychodynamic group research. 51 videotapes, each documenting 90 minutes of a total of three outpatient psychodynamic group therapy sessions, were analyzed with the help of SYMLOG. Results may show the tendency of the importance of receiving statements that promote mentalization as well as directly received speeches as predictors for both factors.

Invited Talk

In this chapter, we aimed to give an illustrative introduction into the physics of solar cells without going into too much detail as those are discussed in solar cell textbooks. Instead, this chapter accounts for applied aspects of perovskite solar cells (PSCs) and addresses students and researchers of various backgrounds. The focus is on how to characterize and interpret efficiency-limiting processes correctly. It advocates for a careful deployment of established characterization methods whose common interpretations might not be readily applicable to PSCs, probable reasons being the thin-film solar cell architecture with a highly emissive absorber or peculiar properties of the perovskite as a mixed ionic–electronic conductor. Therefore, Section 6 is the core of this chapter, where a variety of characterization techniques are reviewed and analyzed using data from PSCs. Prior to this section, the fundamentals of solar cells are briefly introduced in Section 1. Finally, Section 16 deals with what is known about major loss mechanisms in PSCs and their origin in the device architecture, material composition, and microstructure without going into the atomistic levels of their details.

Scan-rate-dependent hysteresis in the current–voltage ( JV ) curve of perovskite solar cells is an important phenomenon that triggered a still ongoing discussion on how to standardize efficiency measurements in perovskites solar cells. From the theoretical point of view, it is interesting and challenging because it is a result of the complex interplay between ionic and electronic conductivity in a photovoltaic device. It is much more than just about the ionic displacement currents themselves, but their effect on charge carrier collection efficiencies and recombination rates at interfaces to adjacent layers. This chapter does not provide a comprehensive summary of the literature on experimental studies on how to alleviate the hysteresis. Instead, it approaches the problem in a systematic way combining theoretical aspects with experimental evidence on the macro- and nanoscale. Therefore, this chapter is at the first place a guide on how to read JV curves of solar cells in general. Additionally, it presents systematic approaches on the characterization of the phenomenon hysteresis including the parameters that govern it. Microscopic origins and remaining open questions are addressed as well. After having read this chapter, the reader should have obtained deep knowledge about the most important and most common solar-cell characterization technique.

Invited Talk

Perovskite solar cells suffer from various instabilities on all time scales. Some of them are driven by light, in particular when employing compounds with mixed halides. Such light soaking effects have been observed in performance changes of solar-cell devices. They have also been spectroscopically investigated in detail on films, where the formation of a low-gap iodine rich phase, seen in a red shift of the PL has been made responsible for a reduced open-circuit voltage. However, studies synchronously examining device performance and its relation to spectroscopy data, are scarce. Here, we perform an in-operandum study, where we investigate changes of open-circuit voltage (Voc) and photocurrent during light soaking and complement it with photo- (PL) and electroluminescence (EL) data on devices, which allow analysis of the Voc-limiting processes using optical and optoelectronic reciprocity relations. We find that changes in the Voc for stable single halide compositions are quantitatively correlated with changes in the PL intensity, showing that the Voc follows changes in the quasi-Fermi level splitting. In contrast, changes in Voc for the mixed halide composition are not correlated to the emergence of the low-gap phase, confirming that this phase is not the sole culprit for a low and instable Voc. Instead, non-radiative voltage losses influenced by mobile ions are dominant in devices containing compositions with high Br content. Interestingly, the low-gap phase contributes less to photocurrent, as seen by a wavelength-dependent PL quenching at short circuit. This observation might be explained by the formation of emissive but partially insulated iodine-rich regions in the film. Such an effect is also possible for single halide systems, when the perovskite composition is not stable, seen in an increase of PL at short circuit during light soaking. This indicates that ion migration in general causes photovoltaically inactive regions, without enhancing non-radiative reco, Perovskite solar cells suffer from various instabilities on all time scales. Some of them are driven by light, in particular when employing compounds with mixed halides. Such light soaking effects have been observed in performance changes of solar-cell devices. They have also been spectroscopically investigated in detail on films, where the formation of a low-gap iodine rich phase, seen in a red shift of the PL has been made responsible for a reduced open-circuit voltage. However, studies synchronously examining device performance and its relation to spectroscopy data, are scarce. Here, we perform an in-operandum study, where we investigate changes of open-circuit voltage (Voc) and photocurrent during light soaking and complement it with photo- (PL) and electroluminescence (EL) data on devices, which allow analysis of the Voc-limiting processes using optical and optoelectronic reciprocity relations. We find that changes in the Voc for stable single halide compositions are quantitatively correlated with changes in the PL intensity, showing that the Voc follows changes in the quasi-Fermi level splitting. In contrast, changes in Voc for the mixed halide composition are not correlated to the emergence of the low-gap phase, confirming that this phase is not the sole culprit for a low and instable Voc. Instead, non-radiative voltage losses influenced by mobile ions are dominant in devices containing compositions with high Br content. Interestingly, the low-gap phase contributes less to photocurrent, as seen by a wavelength-dependent PL quenching at short circuit. This observation might be explained by the formation of emissive but partially insulated iodine-rich regions in the film. Such an effect is also possible for single halide systems, when the perovskite composition is not stable, seen in an increase of PL at short circuit during light soaking. This indicates that ion migration in general causes photovoltaically inactive regions, without enhancing non-radiative reco

Inorganic perovskite based solar cells (PSCs) have been receiving unprecedented attention worldwide in the past several years due to their higher intrinsic stability towards high temperatures and high theoretical power conversion efficiencies. Since a photovoltaic performance of 20.37% has been achieved for inorganic PSCs recently, the operational stability of these devices has become the major bottleneck which impedes their commercialization. The high thermal stability associated with inorganic perovskites comes along with poorer phase stability compared to their hybrid counterparts and therefore needs thorough understanding. Lattice strain and vacancies within the perovskite crystals are found to be the origin of these phase instability issues. This review summarizes the progress in stability research on inorganic perovskites. Specifically, the degradation mechanisms of inorganic perovskites towards temperature, moisture and oxygen are summarized and discussed. Solutions for tackling these stability issues are reviewed and an outlook on further strategies is provided.

Chapter 4

Cs2AgBiBr6 has attracted much interest as a potential lead-free alternative for perovskite solar cells. Although this material offers encouraging optoelectronic features, severe bottlenecks limit the performance of the resulting solar cells to a power conversion efficiency of below 3%. Here, the performance-limiting factors of this material are investigated in full solar cells featuring various architectures. It is found that the photovoltaic parameters of Cs2AgBiBr6-based solar cells strongly depend on the scan speed of the J/V measurements, suggesting a strong impact of ionic conductivity in the material. Moreover, a sign change of the photocurrent for bias voltages above 0.9 V during the measurement of the external quantum efficiency (EQE) is revealed, which can be explained by non-selective contacts. The radiative loss of the VOC from sensitive subgap-EQE measurements is calculated and it is revealed that the loss is caused by a low external luminescence yield and therefore a high non-radiative recombination, supported by the first report of a strongly red shifted electroluminescence signal between 800 and 1000 nm. Altogether, these results point to a poor selectivity of the contacts and charge transport layers, caused by poor energy level alignment that can be overcome by optimizing the architecture of the solar cell.