Perovskite solar cells (PSCs) hold significant promise as the next-generation materials in photovoltaic markets, owing to their ability to achieve impressive power conversion efficiencies, streamlined fabrication processes, cost-effective manufacturing, and numerous other advantages. The utilization of self-assembled monolayer (SAM) molecules has proven to be a significant success in enhancing device efficiency and extending device stability. This review highlights the dual use of SAM molecules in the realm of PSCs, which can not only serve as charge transport materials but also act as interfacial modulators. These research endeavors encompass a wide range of applications for various SAM molecules in both n-i-p and p-i-n structured PSCs, providing a deep insight into the underlying mechanisms. Furthermore, this review proposes current research challenges for future investigations into SAM materials. This timely and thorough review seeks to provide direction and inspiration for current research efforts dedicated to the ongoing incorporation of SAMs in the field of perovskite photovoltaics. Self-assembled monolayer (SAM) molecules are extensively employed in perovskite solar cells, serving both as charge transport materials and interfacial modulators. These molecules play a crucial role in adjusting surface energy levels, reducing interfacial trap defects, and enhancing perovskite crystallization quality, thereby leading to improved performance and stability of perovskite solar cells. image

The stabilization of grain boundaries and surfaces of the perovskite layer is critical to extend the durability of perovskite solar cells. Here we introduced a sulfonium-based molecule, dimethylphenethylsulfonium iodide (DMPESI), for the post-deposition treatment of formamidinium lead iodide perovskite films. The treated films show improved stability upon light soaking and remains in the black α phase after two years ageing under ambient condition without encapsulation. The DMPESI-treated perovskite solar cells show less than 1% performance loss after more than 4,500 h at maximum power point tracking, yielding a theoretical T 80 of over nine years under continuous 1-sun illumination. The solar cells also display less than 5% power conversion efficiency drops under various ageing conditions, including 100 thermal cycles between 25 °C and 85 °C and an 1,050-h damp heat test.

While perovskite photovoltaic (PV) devices are on the verge of commercialization, promising methods to recycle or remanufacture fully encapsulated perovskite solar cells (PSCs) and modules are still missing. Through a detailed life-cycle assessment shown in this work, we identify that the majority of the greenhouse gas emissions can be reduced by re-using the glass substrate and parts of the PV cells. Based on these analytical findings, we develop a novel thermally assisted mechanochemical approach to remove the encapsulants, the electrode, and the perovskite absorber, allowing reuse of most of the device constituents for remanufacturing PSCs, which recovered nearly 90% of their initial performance. Notably, this is the first experimental demonstration of remanufacturing PSCs with an encapsulant and an edge-seal, which are necessary for commercial perovskite solar modules. This approach distinguishes itself from the "traditional" recycling methods previously demonstrated in perovskite literature by allowing direct reuse of bulk materials with high environmental impact. Thus, such a remanufacturing strategy becomes even more favorable than recycling, and it allows us to save up to 33% of the module's global warming potential. Remarkably, this process most likely can be universally applied to other PSC architectures, particularly n-i-p-based architectures that rely on inorganic metal oxide layers deposited on glass substrates. Finally, we demonstrate that the CO2-footprint of these remanufactured devices can become less than 30 g/kWh, which is the value for state-of-the-art c-Si PV modules, and can even reach 15 g/kWh assuming a similar lifetime.

A thin layer of sputtered or wet‐processed nickel oxide (NiO x ) is often used to fabricate perovskite solar cells (PSCs). Remarkably, NiO x can also be deposited by a recently developed electrochemical method, which is considered promising due to its short processing time, absence of high‐vacuum conditions, and ease of manufacturing. Such electrochemically deposited NiO x (eleNiO x ) is obtained by applying an electric bias to the front electrode of a PSC or perovskite solar module (PSM). Therefore, the electrode sheet resistance affects the current distribution through it, creating a gradient in the amount of charge provided for the electrochemical reaction. Consequently, this leads to the inhomogeneity in the formed eleNiO x , which has numerous implications on the final photovoltaic performance of PSMs. In this work, the interdependencies between the electrode sheet resistance, current distribution, eleNiO x thickness gradient, and the caused power losses of large area PSMs are discussed. By coupling the experimental findings with our numerical simulations, it is found that heterogeneity in surface potential of even small‐sized modules can lead to severe differences in local eleNiO x thickness and photovoltaic performance. Therefore the potential drop across the front electrode is an inherent problem of this deposition method and potential approaches are proposed to minimize it.

Photovoltaics (PV) is the most important energy conversion technology for cost-efficient climate change mitigation. To reach the international climate goals, the annual PV module production capacity must be expanded to multi-terawatt scale. Economic and resource constraints demand the implementation cost-efficient multi-junction technologies, for which perovskite-based tandem technologies are highly promising. In this work, the resource demand of the emerging perovskite PV technology is investigated, considering two factors of supply criticality, namely mining capacity for minerals, as well as production capacity for synthetic materials. Overall, the expansion of perovskite PV to a multi-terawatt scale may not be limited by material supply if certain materials, especially cesium and indium, can be replaced. Moreover, organic charge transport materials face unresolved scalability challenges. This study demonstrates that, besides the improvement of efficiency and stability, perovskite PV research needs also to be guided by sustainable materials choices and design-for-recycling considerations.

Fully textured perovskite silicon tandem solar cells are promising for future low-cost photovoltaic deployment. However, the fill factor and open-circuit voltage of these devices are currently limited by the high density of defects at grain boundaries and at interfaces with charge transport layers. To address this, we devise a strategy to simultaneously enhance perovskite crystallization and passivate the perovskite/C-60 interface. By incorporating urea (CO(NH2)(2)) as an additive in the solution step of the hybrid evaporation/spincoating perovskite deposition method, the crystallization kinetics are accelerated, leading to the formation of the desired photoactive phase at room temperature. With that, perovskite films with large grain sizes (>1 mu m) and improved optoelectronic quality are formed at low annealing temperatures (100 degrees C). Concurrently, remnant urea molecules are expelled at the perovskite surface, which locally displaces the C-60 layer, thus reducing interfacial non-radiative recombination losses. With this strategy, the resulting tandem solar cells achieve 30.0% power conversion efficiency.

Phenylguanidine, a strong ligand in the precursor solution, retards crystallization to enlarge grain sizes and reduce defect density of a perovskite film, demonstrating excellent universality across various compositions.

In a recent issue of Joule, Xu andco-workers 1 demonstrated that the 2-terminal perovskite/silicon tandem solar cells are phenomenally resilient to reverse bias because most of the negative voltage in these cells is dropped across the silicon sub-cell, which thereby effectively protects the perovskite one.

This chapter discusses a range of characterization methods that facilitate a deeper understanding of mesoscopic perovskite solar cells (PSCs). It begins with methods to study the layer quality of the mesoscopic contact cell before perovskite filling. The chapter introduces the necessary methods to study chemical–physical material and crystal properties and presents their applicability to mesoscopic PSC. This is followed by discussion of spatially-resolved photophysical methods such as photoluminescence imaging, which are typically carried out when the system is in steady-state. In PSCs, the opportunity to examine the layered form helps in the detailed investigation of the perovskite layer after its fabrication. Microscopically resolved optoelectronic methods provide spatial information on the fundamental physical properties of the solar cell. The I–V characteristic represents the most important measured property of a solar cell from the application point of view.

A sacrificial film of polystyrene nanoparticles was utilized to introduce nano-cavities into mesoporous metal oxide layers. This enabled the growth of larger perovskite crystals inside the oxide scaffold with significantly suppressed non-radiative recombination and improved device performance. This work exemplifies potential applications of such nanoarchitectonic approaches in perovskite opto-electronic devices.

Carbon‐based electrodes represent a promising approach to improve stability and up‐scalability of perovskite photovoltaics. The temperature at which these contacts are processed defines the absorber grain size of the perovskite solar cell: in cells with low‐temperature carbon‐based electrodes (L‐CPSCs), layer‐by‐layer deposition is possible, allowing perovskite crystals to be large (>100 nm), while in cells with high‐temperature carbon‐based contacts (H‐CPSCs), crystals are constrained to 10–20 nm in size. To enhance the power conversion efficiency of these devices, the main loss mechanisms are identified for both systems. Measurements of charge carrier lifetime, quasi‐Fermi level splitting (QFLS) and light‐intensity‐dependent behavior, supported by numerical simulations, clearly demonstrate that H‐CPSCs strongly suffer from non‐radiative losses in the perovskite absorber, primarily due to numerous grain boundaries. In contrast, large crystals of L‐CPSCs provide a long carrier lifetime (1.8 µs) and exceptionally high QFLS of 1.21 eV for an absorber bandgap of 1.6 eV. These favorable characteristics explain the remarkable open‐circuit voltage of over 1.1 V in hole‐selective layer‐free L‐CPSCs. However, the low photon absorption and poor charge transport in these cells limit their potential. Finally, effective strategies are provided to reduce non‐radiative losses in H‐CPSCs, transport losses in L‐CPSCs, and to improve photon management in both cell types.

Interface engineering and passivating contacts are key enablers to reach the highest efficiencies in photovoltaic devices. While printed carbon–graphite back electrodes for hole‐transporting material (HTM)‐free perovskite solar cells (PSCs) are appealing for fast commercialization of PSCs due to low processing costs and extraordinary stability, this device architecture so far suffers from severe performance losses at the back electrode interface. Herein, a 2D perovskite passivation layer as an electron blocking layer (EBL) at this interface to substantially reduce interfacial recombination losses is introduced. The formation of the 2D perovskite EBL is confirmed through X‐ray diffraction, photoemission spectroscopy, and an advanced spectrally resolved photoluminescence microscopy mapping technique. Reduced losses that lead to an enhanced fill factor and VOC are quantified by electrochemical impedance spectroscopy and JSC–VOC measurements. This enables reaching one of the highest reported efficiencies of 18.5% for HTM‐free PSCs using 2D perovskite as an EBL with a significantly improved device stability.

We propose a novel approach for microscopically resolved photocurrent imaging. The method is based on the notion that electrical bias-dependent photoluminescence images reveal fundamental information on charge extraction of photovoltaic devices. The approach is derived from basic physical principles and verified by means of a near-to-ideal III-V solar cell. It is demonstrated that the approach is of special relevance for liquid-processed perovskite solar cells. We outline the potential to investigate the local charge extraction efficiency, which can be related to fundamental charge extraction properties associated with the quality of interfaces and morphological defects from device processing. The method demonstrates that photoluminescence imaging can be a powerful tool for device optimization as well as fundamental studies when carried out at different bias voltages.

The photocurrent density-voltage ( J ( V )) curve is the fundamental characteristic to assess opto-electronic devices, in particular solar cells. However, it only yields information on the performance integrated over the entire active device area. Here, a method to determine a spatially resolved photocurrent image by voltage-dependent photoluminescence microscopy is derived from basic principles. The opportunities and limitations of the approach are studied by the investigation of III-V and perovskite solar cells. This approach allows the real-time assessment of the microscopically resolved local J ( V ) curve, the steady-state J sc , as well as transient effects. In addition, the measurement contains information on local charge extraction and interfacial recombination. This facilitates the identification of regions of non-ideal charge extraction in the solar cells and enables to link these to the processing conditions. The proposed technique highlights that, combined with potentiostatic measurements, luminescence microscopy turns out to be a powerful tool for the assessment of performance losses and the improvement of solar cells.

Carbon‐electrode‐based perovskite solar cells (C‐PSCs) are promising candidates for commercialization due to their high stability. However, the absence of a hole selective layer (HSL) often limits their performance, yielding low fill factors (FFs). Herein, a certified FF of 78.8% obtained through HSL‐free C‐PSCs is focused. This is found to approach the highest values reported for metal‐electrode‐based PSCs employing highly selective HSLs. The loss mechanisms affecting the FF in fully printed HSL‐free C‐PSCs are thus investigated. Methods commonly used to analyze and quantify the impact of recombination and transport losses on the FF of established photovoltage devices are assessed, and their applicability in C‐PSCs is examined. In the improved devices, non‐radiative recombination contributes to only 3%abs loss with respect to the FF in the radiative limit, which is attributed to an optimal diode ideality factor approaching 1.0. Moreover, contributions of shunt resistive losses are determined to be negligible. Interfacial series resistance losses at the perovskite/carbon interface are identified as the main loss channel, highlighting the importance of the quality of the contact between the perovskite and the back‐contact electrode.