Unraveling the Role of Perovskite in Buried Interface Passivation

Terthiophene-Based Dopant-Free Hole-Transporting Materials for Inverted Perovskite Solar Cells

The interfaces of perovskite solar cells are essential for high power conversion efficiency and long-term stability. This study showcases two innovative materials, WZ40 and WZ102, triarylamine end-capped functionalized terthiophene derivatives. These materials serve as hole-transporting materials (HTMs), enabling the production of efficient mixed-halide inverted perovskite solar cells. Both HTMs exhibit impressive thermal stability with decomposition temperatures over 415 °C, making them suitable for developing stable perovskite solar cells. Their sulfur-rich terthiophene core enhances perovskite stability through Pb-S interactions, promoting uniform crystal growth. By adjusting the electron density in WZ40 and WZ102 through donor and acceptor group modifications, energy level alignment at the HTM/perovskite interface is optimized, facilitating efficient hole transfer. The donor-rich WZ102-based solar cell achieves an outstanding open-circuit voltage of 1.09 V and a power conversion efficiency of close to 20%, thanks to effective hole transport and low series resistance. This work introduces a promising class of terthiophene-based small molecules as HTMs, paving the way for dopant-free interface materials and advancing the commercialization of perovskite solar cells.

Decoding recombination dynamics in perovskite solar cells: an in-depth critical review

The remarkable optoelectronic properties of metal halide perovskites (MHPs) have established them as highly promising photovoltaic absorber materials, propelling the rapid advancement of perovskite solar cells (PSCs) that outperform many traditional alternatives in terms of power conversion efficiency (PCE). However, despite their advancements, PSC devices encounter significant non-radiative recombination losses, encompassing trap-assisted (Shockley-Read-Hall) recombination in bulk and interfaces of PSCs, which restricts their open-circuit voltage (VOC) and overall PCE, dragging it below the Shockley-Queisser (SQ) limit. The ongoing debate regarding the role of grain boundary (GB) recombination, whether it primarily manifests as bulk or surface recombination, has spurred extensive research aimed at elucidating these mechanisms. This review provides a critical comprehensive analysis of the thermodynamic correlations related to VOC losses, bridging the gap between the theoretical SQ limit and practical device performance. Subsequently, it delves into recent findings that aim to decipher the multifaced nature and origin of radiative and non-radiative recombination-induced losses within the device stack, assessing their impacts on overall performance. Furthermore, this review emphasizes the application of advanced machine learning techniques to discern dominant recombination mechanisms in PSCs. Finally, it summarizes the notable advanced strategies to mitigate undesirable non-radiative recombination losses, which pave the way to the thermodynamic efficiency limit.

Photosensitivity and Carrier Densities of Perovskite Solar Absorbers

Dark and light current-voltage characteristics of perovskite solar absorbers are analyzed in terms of their carrier densities. The analysis reveals p-type large polarons as a dominant carrier type in the investigated perovskite solar cells. The mechanism causing photosensitivity is attributed to the dissociation (and pairing) of bipolarons to large polarons (and vice versa) that are controlled by the internal potential Γ. As an example, the polaron concept is tested for a formamidinium lead triiodide perovskite solar cell. The individual steps of the data analysis are demonstrated and determine the ionicity factor of this perovskite film, quantify the density of the large polarons, and predict the gain and loss of photo-induced carriers. It is deduced that a reversible light-on/off operation can only occur when the bias voltage never exceeds a critical value of the internal potential. The results gained in this study suggest that the novel analysis can be successively applied on different hybrid perovskite materials, too.

Engineering of buried interfaces in perovskites: advancing sustainable photovoltaics

Perovskite solar cells (PSCs) have garnered significant attention for their high power conversion efficiency (PCE) and potential for cost-effective, large-scale manufacturing. This comprehensive review focuses on the role of buried interface engineering in enhancing the performance and stability of PSCs with both n-type electron transport layer/perovskite/p-type hole transport layer (n-i-p) and p-type hole transport layer/perovskite/n-type electron transport layer (p-i-n) structures. This study highlights key challenges associated with interface engineering, such as charge extraction, recombination loss, and energy level alignment. Various interface engineering techniques, such as surface passivation, self-assembled monolayers, and additive engineering, are explored in terms of their effectiveness in mitigating recombination loss and improving long-term device stability. This review also provides an in-depth analysis of material selection for the electron and hole transport layers, defect management techniques, and the influence of these on perovskite film quality and device stability. Advanced characterization methods for buried interfaces are discussed, providing insights into the structural, morphological, and electronic properties that govern device performance. Furthermore, we explore emerging approaches that target homogenous cation distribution and phase stability at buried interfaces, both of which are crucial for improving PCEs beyond current benchmarks. By synthesizing the latest research findings and identifying key challenges, this review aims to guide future directions in interface engineering for PSCs and ensure their successful use in next-generation sustainable energy technologies.

Defect Engineering at Buried Interface of Perovskite Solar Cells

Perovskite solar cells (PSC) have developed rapidly since the past decade with the aim to produce highly efficient photovoltaic technology at a low cost. Recently, physical and chemical defects at the buried interface of PSC including vacancies, impurities, lattice strain, and voids are identified as the next formidable hurdle to the further advancement of the performance of devices. The presence of these defects has unfavorably impacted many optoelectronic properties in the PSC, such as band alignment, charge extraction/recombination dynamics, ion migration behavior, and hydrophobicity. Herein, a broad but critical discussion on various essential aspects related to defects at the buried interface is provided. In particular, the defects existing at the surface of the underlying charge transporting layer (CTL) and the bottom surface of the perovskite film are initially elaborated. In situ and ex situ characterization approaches adopted to unveil hidden defects are elucidated to determine their influence on the efficiency, operational stability, and photocurrent-voltage hysteresis of PSC. A myriad of innovative strategies including defect management in CTL, the introduction of passivation materials, strain engineering, and morphological control used to address defects are also systematically elucidated to catalyze the further development of more efficient, reliable, and commercially viable photovoltaic devices.

Enhancing the Efficiency and Stability of Inverted Formamidinium-Cesium Lead-Triiodide Perovskite Solar Cells through Lewis Base Pretreatment of Buried Interfaces

Mixed components of formamidinium(FA) and cesium (Cs)-based perovskite solar cells are the most hopeful for commercialization owing to their excellent operational and phase stabilities, especially for devices with inverted structure. The nonradiative recombination of carriers can be effectively suppressed through interface optimization, therefore, the performance of devices can be improved. Notably, the buried interface emerges as critical aspects such as charge transport, charge recombination kinetics, and morphology of perovskite films. This study focuses on a straightforward yet effective approach to overcome buried interface challenges between organic polymers (poly(-triarylamine) (PTAA) and FACs-based perovskite films. The PTAA substrate is pretreated with a Lewis base known as 2-butynoic acid (BA) with a C═O functional group. First, it can be an interfacial buffering layer, harmonizing stress mismatch between the perovskite and PTAA layers, consequently optimizing crystallization and improving perovskite film quality. Second, Pb2+ defect can be passivated at the buried interface of the perovskite film through binding with the C═O group of the BA molecule. This dual-function strategy leads to a substantial enhancement in both photoelectric conversion efficiency (PCE) and stability of devices. Finally, the PCE of the device-modified buried interface with BA reaches an impressive 23.33%. Furthermore, unencapsulated devices with BA treatment maintain approximately 94% of their initial efficiency after aging at maximum power point tracking for 1000 h.

SnO2-Perovskite Interface Engineering Based on Bifacial Passivation via Multifunctional N-(2-Acetamido)-2-aminoethanesulfonic Acid toward Efficient and Stable Solar Cells

Bifacial passivation on both electron transport materials and perovskite light-absorbing layers as a straightforward technique is used for gaining efficient and stable perovskite solar cells (PSCs). To develop this strategy, organic molecules containing multiple functional groups can maximize the effect of defect suppression. Based on this, we introduce N-(2-acetamido)-2-aminoethanesulfonic acid (ACES) at the interface between tin oxide (SnO2) and perovskite. The synergistic effect of multiple functional groups in ACES, including amino, carbonyl (C═O), and sulfonic acid (S═O) groups, promotes charge extraction of SnO2 and provides an improved energy level alignment for charge transfer. Furthermore, S═O in ACES effectively passivates the defects of uncoordinated Pb2+ in perovskite films, resulting in enhanced crystallinity and decreased nonradiative recombination at the buried interface. The power conversion efficiency (PCE) of related PSCs increases from 20.21% to 22.65% with reduced J-V hysteresis after interface modification with ACES. Notably, upon being stored at a low relative humidity of 40 ± 5% over 2000 h and high relative humidity of 80 ± 5% over 1000 h, the unencapsulated ACES-modified device retains up to 90% and 80% of their initial PCE, respectively. This study deepens defect passivation engineering on the buried interface of perovskites for realizing efficient and stable solar cells.