Leyu Bi

Self-assembled monolayers (SAMs) are widely employed as effective hole-selective layers (HSLs) in inverted perovskite solar cells (PSCs). However, most SAM molecules are amphiphilic in nature and tend to form micelles in the commonly used alcoholic processing solvents. This introduces an extra energetic barrier to disassemble the micelles during the binding of SAM molecules on the substrate surface, limiting the formation of a compact SAM. To alleviate this problem for achieving optimal SAM growth, a co-solvent strategy to disassemble the micelles of carbazole-based SAM molecules in the processing solution is developed. This effectively increases the critical micelle concentration to be above the processing concentration and enhances the reactivity of the phosphonic acid anchoring group to allow densely packed SAMs to be formed on indium tin oxide. Consequently, the PSCs derived from using MeO-2PACz, 2PACz, and CbzNaph SAM HSLs show universally improved performance, with the CbzNaph SAM-derived device achieving a champion efficiency of 24.98% and improved stability.

Abstract The buried interface in perovskite solar cells (PSCs) is pivotal for achieving high efficiency and stability. However, it is challenging to study and optimize the buried interface due to its non‐exposed feature. Here, a facile and effective strategy is developed to modify the SnO 2 /perovskite buried interface by passivating the buried defects in perovskite and modulating carrier dynamics via incorporating formamidine oxalate (FOA) in SnO 2 nanoparticles. Both formamidinium and oxalate ions show a longitudinal gradient distribution in the SnO 2 layer, mainly accumulating at the SnO 2 /perovskite buried interface, which enables high‐quality upper perovskite films, minimized defects, superior interface contacts, and matched energy levels between perovskite and SnO 2 . Significantly, FOA can simultaneously reduce the oxygen vacancies and tin interstitial defects on the SnO 2 surface and the FA + /Pb 2+ associated defects at the perovskite buried interface. Consequently, the FOA treatment significantly improves the efficiency of the PSCs from 22.40% to 25.05% and their storage‐ and photo‐stability. This method provides an effective target therapy of buried interface in PSCs to achieve very high efficiency and stability.

Functional additives that can interact with the perovskite precursors to form the intermediate phase have been proven essential in obtaining uniform and stable α-FAPbI3 films. Among them, Cl-based volatile additives are the most prevalent in the literature. However, their exact role is still unclear, especially in inverted perovskite solar cells (PSCs). In this work, we have systematically studied the functions of Cl-based volatile additives and MA-based additives in formamidinium lead iodide (FAPbI3)-based inverted PSCs. Using in situ photoluminescence, we provide clear evidence to unravel the different roles of volatile additives (NH4Cl, FACl, and MACl) and MA-based additives (MACl, MABr, and MAI) in the nucleation, crystallization, and phase transition of FAPbI3. Three different kinds of crystallization routes are proposed based on the above additives. The non-MA volatile additives (NH4Cl and FACl) were found to promote crystallization and lower the phase-transition temperatures. The MA-based additives could quickly induce MA-rich nuclei to form pure α-phase FAPbI3 and dramatically reduce phase-transition temperatures. Furthermore, volatile MACl provides a unique effect on promoting the growth of secondary crystallization during annealing. The optimized solar cells with MACl can achieve an efficiency of 23.1%, which is the highest in inverted FAPbI3-based PSCs.

Abstract Inverted perovskite solar cells (PSCs) have attracted considerable attention due to their distinct advantages, including minimal hysteresis, cost‐effectiveness, and suitability for tandem applications. Nevertheless, the solution processing and the low formation energy of perovskites inevitably lead to numerous defects formed at both the bulk and interfaces of the perovskite layer. These defects can act as non‐radiative recombination centers, significantly impeding carrier transport and posing a substantial obstacle to stability and further enhancing power conversion efficiency (PCE). This review delves into a detailed discussion of the nature and origin of defects and the characterization techniques employed for defect identification. Furthermore, it systematically summarizes methods for defect detection and approaches for passivating interface and bulk defects within the perovskite film in inverted PSCs. Finally, this review offers a perspective on employing upscaling defect passivation engineering for perovskite modules. It is hoped this review provides insights into defect passivation in inverted PSCs and solar modules.

Despite the rapidly increased power conversion efficiency (PCE) of perovskite solar cells (PVSCs), it is still quite challenging to bring such promising photovoltaic technology to commercialization. One of the challenges is the upscaling from small-sized lab devices to large-scale modules or panels for production. Currently, most of the efficient inverted PVSCs are fabricated on top of poly[bis(4-phenyl)(2, 4, 6-trimethylphenyl)amine] (PTAA), which is a commonly used hole-transporting material, using spin-coating method to be incompatible with large-scale film deposition. Therefore, it is important to develop proper coating methods such as blade-coating or slot-die coating that can be compatible for producing large-area, high-quality perovskite thin films. It is found that due to the poor wettability of PTAA, the blade-coated perovskite films on PTAA surface are often inhomogeneous with large number of voids at the buried interface of the perovskite layer. To solve this problem, self-assembled monolayer (SAM)-based hole-extraction layer (HEL) with tunable headgroups on top of the SAM can be modified to provide better wettability and facilitate better interactions with the perovskite coated on top to passivate the interfacial defects. The more hydrophilic SAM surface can also facilitate the nucleation and growth of perovskite films fabricated by blade-coating methods, forming a compact and uniform buried interface. In addition, the SAM molecules can also be modified so their highest occupied molecular orbital (HOMO) levels can have a better energy alignment with the valence band maxima (VBM) of perovskite. Benefitted by the high-quality buried interface of perovskite on SAM-based substrate, the champion device shows a PCE of 18.47% and 14.64% for the devices with active areas of 0.105 cm² and 1.008 cm², respectively. In addition, the SAM-based device exhibits decent stability, which can maintain 90% of its initial efficiency after continuous operation for over 500 h at 40 ℃ in inert atmosphere. Moreover, the SAM-based perovskite mini-module exhibits a PCE of 14.13% with an aperture area of 18.0 cm². This work demonstrates the great potential of using SAMs as efficient HELs for upscaling PVSCs and producing high-quality buried interface for large-area perovskite films.