Anchorable Polymers Enabling Ultra-Thin and Robust Hole-Transporting Layers for High-Efficiency Inverted Perovskite Solar Cells.

Currently, the development of polymeric hole-transporting materials (HTMs) lags behind that of small-molecule HTMs in inverted perovskite solar cells (PSCs). A critical challenge is that conventional polymeric HTMs are incapable of forming ultra-thin and conformal coatings like self-assembly monolayers (SAMs), especially for substrates with rough surface morphology. Herein, we address this challenge by designing anchorable polymeric HTMs (CP1 to CP5).

Highly Efficient Monolithic Perovskite/TOPCon Silicon Tandem Solar Cells Enabled by "Halide Locking".

Perovskite/silicon tandem solar cells (TSCs) are promising candidates for commercialization due to their outstanding power conversion efficiencies (PCEs). However, controlling the crystallization process and alleviating the phases/composition inhomogeneity represent a considerable challenge for perovskite layers grown on rough silicon substrates, ultimately limiting the efficiency and stability of TSC. Here, this study reports a "halide locking" strategy that simultaneously modulates the nucleation and crystal growth process of wide bandgap perovskites by introducing a multifunctional ammonium salt, thioacetylacetamide hydrochloride (TAACl), to bind with all types of cations and anions in the mixed halide perovskite precursor.

Optimization of Charge Extraction and Interconnecting Layers for Highly Efficient Perovskite/Organic Tandem Solar Cells with High Fill Factor.

Perovskite/organic tandem solar cells (POTSCs) have garnered significant attention due to their potential for achieving high photovoltaic (PV) performance. However, the reported power conversion efficiencies (PCEs) and fill factors (FFs) are still subpar due to the challenges associated with charge extraction in the organic bulk-heterojunction (BHJ) and significant energy losses in the interconnecting layers (ICLs). Here, a quaternary organic BHJ blend is developed to enhance the charge extraction in the organic subcell, contributing to an increased FF of ≥78% under 1 sun illumination and even more under lower illumination intensities.

Narrow Bandgap Metal Halide Perovskites for All-Perovskite Tandem Photovoltaics.

All-perovskite tandem solar cells are attracting considerable interest in photovoltaics research, owing to their potential to surpass the theoretical efficiency limit of single-junction cells, in a cost-effective sustainable manner. Thanks to the bandgap-bowing effect, mixed tin-lead (Sn-Pb) perovskites possess a close to ideal narrow bandgap for constructing tandem cells, matched with wide-bandgap neat lead-based counterparts. The performance of all-perovskite tandems, however, has yet to reach its efficiency potential.

Unveiling the Potential of Ambient Air Annealing for Highly Efficient Inorganic CsPbI Perovskite Solar Cells.

Here, we report a detailed surface analysis of dry- and ambient air-annealed CsPbI films and their subsequent modified interfaces in perovskite solar cells. We revealed that annealing in ambient air does not adversely affect the optoelectronic properties of the semiconducting film; instead, ambient air-annealed samples undergo a surface modification, causing an enhancement of band bending, as determined by hard X-ray photoelectron spectroscopy measurements. We observe interface charge carrier dynamics changes, improving the charge carrier extraction in CsPbI perovskite solar cells.

Interface Modification for Energy Level Alignment and Charge Extraction in CsPbI Perovskite Solar Cells.

In perovskite solar cells (PSCs) energy level alignment and charge extraction at the interfaces are the essential factors directly affecting the device performance. In this work, we present a modified interface between all-inorganic CsPbI perovskite and its hole-selective contact (spiro-OMeTAD), realized by the dipole molecule trioctylphosphine oxide (TOPO), to align the energy levels. On a passivated perovskite film, with -octylammonium iodide (OAI), we created an upward surface band-bending at the interface by TOPO treatment.

Interface engineering for high-performance, triple-halide perovskite-silicon tandem solar cells.

Improved stability and efficiency of two-terminal monolithic perovskite-silicon tandem solar cells will require reductions in recombination losses. By combining a triple-halide perovskite (1.68 electron volt bandgap) with a piperazinium iodide interfacial modification, we improved the band alignment, reduced nonradiative recombination losses, and enhanced charge extraction at the electron-selective contact.

Determination of Mobile Ion Densities in Halide Perovskites via Low-Frequency Capacitance and Charge Extraction Techniques.

Mobile ions in perovskite photovoltaic devices can hinder performance and cause degradation by impeding charge extraction and screening the internal field. Accurately quantifying mobile ion densities remains a challenge and is a highly debated topic. We assess the suitability of several experimental methodologies for determining mobile ion densities by using drift-diffusion simulations.

Minimizing buried interfacial defects for efficient inverted perovskite solar cells.

Controlling the perovskite morphology and defects at the buried perovskite-substrate interface is challenging for inverted perovskite solar cells. In this work, we report an amphiphilic molecular hole transporter, (2-(4-(bis(4-methoxyphenyl)amino)phenyl)-1-cyanovinyl)phosphonic acid, that features a multifunctional cyanovinyl phosphonic acid group and forms a superwetting underlayer for perovskite deposition, which enables high-quality perovskite films with minimized defects at the buried interface. The resulting perovskite film has a photoluminescence quantum yield of 17% and a Shockley-Read-Hall lifetime of nearly 7 microseconds and achieved a certified power conversion efficiency (PCE) of 25.

Internal electric fields control triplet formation in halide perovskite-sensitized photon upconverters.

Halide perovskite-based photon upconverters utilize perovskite thin films to sensitize triplet exciton formation in a small-molecule layer, driving triplet-triplet annihilation upconversion. Despite having excellent carrier mobility, these systems suffer from inefficient triplet formation at the perovskite/annihilator interface. We studied triplet formation in formamidinium-methylammonium lead iodide/rubrene bilayers using photoluminescence and surface photovoltage methods.

Improving interface quality for 1-cm all-perovskite tandem solar cells.

All-perovskite tandem solar cells provide high power conversion efficiency at a low cost. Rapid efficiency improvement in small-area (<0.1 cm) tandem solar cells has been primarily driven by advances in low-bandgap (approximately 1.

Open-circuit and short-circuit loss management in wide-gap perovskite p-i-n solar cells.

In this work, we couple theoretical and experimental approaches to understand and reduce the losses of wide bandgap Br-rich perovskite pin devices at open-circuit voltage (V) and short-circuit current (J) conditions. A mismatch between the internal quasi-Fermi level splitting (QFLS) and the external V is detrimental for these devices. We demonstrate that modifying the perovskite top-surface with guanidinium-Br and imidazolium-Br forms a low-dimensional perovskite phase at the n-interface, suppressing the QFLS-V mismatch, and boosting the V.

Overcoming C-induced interfacial recombination in inverted perovskite solar cells by electron-transporting carborane.

Inverted perovskite solar cells still suffer from significant non-radiative recombination losses at the perovskite surface and across the perovskite/C interface, limiting the future development of perovskite-based single- and multi-junction photovoltaics. Therefore, more effective inter- or transport layers are urgently required. To tackle these recombination losses, we introduce ortho-carborane as an interlayer material that has a spherical molecular structure and a three-dimensional aromaticity.

Nano-optical designs for high-efficiency monolithic perovskite-silicon tandem solar cells.

Perovskite-silicon tandem solar cells offer the possibility of overcoming the power conversion efficiency limit of conventional silicon solar cells. Various textured tandem devices have been presented aiming at improved optical performance, but optimizing film growth on surface-textured wafers remains challenging. Here we present perovskite-silicon tandem solar cells with periodic nanotextures that offer various advantages without compromising the material quality of solution-processed perovskite layers.

Static Disorder in Lead Halide Perovskites.

In crystalline and amorphous semiconductors, the temperature-dependent Urbach energy can be determined from the inverse slope of the logarithm of the absorption spectrum and reflects the static and dynamic energetic disorder. Using recent advances in the sensitivity of photocurrent spectroscopy methods, we elucidate the temperature-dependent Urbach energy in lead halide perovskites containing different numbers of cation components. We find Urbach energies at room temperature to be 13.

Photoinduced Energy-Level Realignment at Interfaces between Organic Semiconductors and Metal-Halide Perovskites.

In contrast to the common conception that the interfacial energy-level alignment is affixed once the interface is formed, we demonstrate that heterojunctions between organic semiconductors and metal-halide perovskites exhibit huge energy-level realignment during photoexcitation. Importantly, the photoinduced level shifts occur in the organic component, including the first molecular layer in direct contact with the perovskite. This is caused by charge-carrier accumulation within the organic semiconductor under illumination and the weak electronic coupling between the junction components.

Monolithic perovskite/silicon tandem solar cell with >29% efficiency by enhanced hole extraction.

Tandem solar cells that pair silicon with a metal halide perovskite are a promising option for surpassing the single-cell efficiency limit. We report a monolithic perovskite/silicon tandem with a certified power conversion efficiency of 29.15%.

Defect/Interface Recombination Limited Quasi-Fermi Level Splitting and Open-Circuit Voltage in Mono- and Triple-Cation Perovskite Solar Cells.

Multication metal-halide perovskites exhibit desirable performance and stability, compared to their monocation counterparts. However, the study of the photophysical properties and the nature of defect states in these materials is still a challenging and ongoing task. Here, we study bulk and interfacial energy loss mechanisms in solution-processed MAPbI (MAPI) and (CsPbI)[(FAPbI)(MAPbBr)] (triple cation) perovskite solar cells using absolute photoluminescence (PL) measurements.

Comparing the excited-state properties of a mixed-cation-mixed-halide perovskite to methylammonium lead iodide.

Organic-inorganic perovskites are one of the most promising photovoltaic materials for the design of next generation solar cells. The lead-based perovskite prepared with methylammonium and iodide was the first in demonstrating high power conversion efficiency, and it remains one of the most used materials today. However, perovskites prepared by mixing several halides and several cations systematically yield higher efficiencies than "pure" methylammonium lead iodide (MAPbI) devices.

How To Quantify the Efficiency Potential of Neat Perovskite Films: Perovskite Semiconductors with an Implied Efficiency Exceeding 28.

Perovskite photovoltaic (PV) cells have demonstrated power conversion efficiencies (PCE) that are close to those of monocrystalline silicon cells; however, in contrast to silicon PV, perovskites are not limited by Auger recombination under 1-sun illumination. Nevertheless, compared to GaAs and monocrystalline silicon PV, perovskite cells have significantly lower fill factors due to a combination of resistive and non-radiative recombination losses. This necessitates a deeper understanding of the underlying loss mechanisms and in particular the ideality factor of the cell.

Barrierless Free Charge Generation in the High-Performance PM6:Y6 Bulk Heterojunction Non-Fullerene Solar Cell.

Organic solar cells are currently experiencing a second golden age thanks to the development of novel non-fullerene acceptors (NFAs). Surprisingly, some of these blends exhibit high efficiencies despite a low energy offset at the heterojunction. Herein, free charge generation in the high-performance blend of the donor polymer PM6 with the NFA Y6 is thoroughly investigated as a function of internal field, temperature and excitation energy.