Deep-Level Transient Spectroscopy for Effective Passivator Selection in Perovskite Solar Cells to Attain High Efficiency over 23

Reduction of Nonradiative Recombination at Perovskite/C60 Interface in Inverted Perovskite Solar Cells

Although p-i-n type inverted perovskite solar cells (PSCs) achieve excellent photoelectric efficiencies, the nonradiative recombination at the perovskite/C60 interface is still the key factor affecting the overall efficiency of p-i-n PSCs. Herein, a synergistic passivation strategy (meta-fluoro-phenylethylammonium iodide and piperazine iodide) is developed to modify the perovskite/C60 interface in p-i-n PSCs. This strategy facilitates in situ reconstruction of the perovskite film to obtain a smooth and flat perovskite surface. Furthermore, the two molecules work synergistically to passivate surface defects, adjust the interface energy levels, and bolster the interface electric field, all of which reduce the nonradiative recombination losses at the perovskite/C60 interface. The optimal PSCs adopting this strategy achieve a power conversion efficiency of 25.85%. (certified value of 25.22%). After operating at the maximum power point for 1000 h, the 95% initial efficiency can be maintained. Furthermore, this process is universally applicable and scalable.

An Intermediate-Aided Perovskite Phase Purification for High-Performance Solar Cells

In recent years, perovskite solar cells (PSCs) have garnered considerable attention as a prime candidate for next-generation photovoltaic technology. Ensuring the structural stability of perovskites is crucial to the operational reliability of these devices. However, the nonphotoactive yellow phase (δ-FAPbI3) of formamidine (FA)-based perovskites is more favorable in thermodynamics, making it challenging to achieve pure α phase in crystallization. Herein, we introduce a language machine learning approach to analyze suitable additives to achieve the desired phase purification. By fast analyzing ∼106 abstracts in chemistry and materials science, our approach identifies aminoguanidine (AG) hydrochloride as a promising candidate for intermediate phase formation during nucleation. The experiments confirm that AG forms a novel one-dimensional intermediate phase (AGPbI3), which suppresses the solvent intermediate phase and δ-phase formation and promotes development of the α-phase. Consequently, the efficiency of the solar cells increased from 23.99 to 25.46%. The long-term thermal stability and photostability were significantly enhanced owing to the purified α-phase, maintaining 82% of the initial efficiency after 1056 h aging at 85 °C and 94.6% of the initial efficiency after 835 h of illumination in an N2 atmosphere, respectively. This strategy also enhanced the performance of flexible solar cells, increasing their efficiency from 21.24 to 22.86%. This work is designed to fast explore new intermediate phases in improving the efficiency and operation stability of thin-film solar cells.

Charge Transfer and Retention in 2D Passivated Perovskite-C60 Systems

2D perovskites and organic ligands are often implemented as passivating interlayers in perovskite solar cells. Herein, five such passivates are evaluated by using time-resolved spectroscopy to study the carrier dynamics at the perovskite-C60 interface. The impact of passivation on factors such as charge transfer rate, charge retention in the acceptor layers, surface recombination, and uniformity are mapped onto the solar cell performance. The charge transfer was found to take place in tens of nanoseconds, and the charge retention without any passivate lasted a few hundred nanoseconds. The passivate that produced the best solar cells, ethylenediammonium iodide, extended the charge retention time up to one microsecond, which significantly increased the open-circuit voltage. It also had the best uniformity and hence least variance in power conversion efficiency. Curiously, it did not merely adjust surface energy states to enhance charge transfer but also extracted charges by itself without the C60, resulting in higher short-circuit current.

Chirality-Induced Crystallization and Defect Passivation of Perovskites: Toward High-Performance Solar Cells

As an additive for perovskites, in addition to functional groups, the steric configuration of molecules is worthy of consideration because it influences perovskite crystallization, thus determining whether defect passivation is effective without any side effects. In this work, the chiral molecules l- and d-pyroglutamic acid (l-PA and d-PA) were chosen as additives for perovskite passivators to reveal the reasons for the differences in passivation between amino acids with different steric configurations. Functional groups, such as the C═O groups and N-H groups of l-PA and d-PA, can passivate the perovskite defects. However, l-PA exhibited a more distorted steric configuration, while d-PA was more planar, leading to differences in the distances between the two C═O groups. Taking the Pb-Pb bond length as a reference, the shorter distance between the two C═O groups of l-PA distorts the perovskite lattice structure, which results in poor device stability. Conversely, the similar distance between the two C═O groups of d-PA promoted the preferred orientational growth of the perovskite. Finally, the d-PA-doped device accomplished an excellent efficiency of 24.11% with an improved open-circuit voltage of 1.17 V. Furthermore, the efficiency of the unencapsulated d-PA-doped device was maintained at 93% in N2 for more than 3000 h and 74% after 500 h of operation at maximum power point tracking under continuous illumination.

Bifunctional Interface Passivation via Copper Acetylacetonate for Efficient and Stable Perovskite Solar Cells

Manipulating interface defects can minimize interfacial nonradiative recombination, thus increasing the stability and performance of perovskite solar cells (PSCs). Here, copper acetylacetonate [Cu(acac)2] as a passivator is used to treat the interface between Spiro-OMeTAD and perovskite. Owing to the strong chelation, the uncoordinated Pb2+ could react with -C═O/-COH functional groups, firmly anchoring acetylacetonate at this interface or the grain boundaries (GBs) of perovskite films to construct multiple ligand bridges, accompanied by the p-type copper iodide formation with copper substituting lead. Simultaneously, Cu+-Cu2+ pairs transfer electrons from Pb0 to I0, suppressing deep level defects of Pb0 and I0 near the perovskite interface. These can be beneficial to hole-transferring. Moreover, the Schiff base complexes with hydrophobicity, from the reaction of acetylacetonate with perovskite, can lead to tightly packed adjacent perovskite surfaces and self-seal the GBs of the perovskite, inhibiting moisture diffusion for long-term stability. Consequently, the Cu(acac)2-based PSC has achieved more than 24% champion efficiency while retaining ca. 92% of the initial power conversion efficiency after 1680 h of storage.

Rational Design of Ferroelectric 2D Perovskite for Improving the Efficiency of Flexible Perovskite Solar Cells Over 23

Despite the great progress of flexible perovskite solar cells (f-PSCs), it still faces several challenges during the homogeneous fabrication of high-quality perovskite thin films, and overcoming the insufficient exciton dissociation. To the ends, we rationally design the ferroelectric two-dimensional (2D) perovskite based on pyridine heterocyclic ring as the organic interlayer. We uncover that incorporation of the ferroelectric 2D material into 3D perovskite induces an increased built-in electric field (BEF), which enhances the exciton dissociation efficiency in the device. Moreover, the 2D seeds could assist the 3D crystallization by forming more homogeneous and highly-oriented perovskite crystals. As a result, an impressive power conversion efficiency (PCE) over 23 % has been achieved by the f-PSCs with outstanding ambient stability. Moreover, the piezo/ferroelectric 2D perovskite intrigues a decreased hole transport barriers at the ITO/perovskite interface under tensile stress, which opens new possibilities for developing highly-efficient f-PSCs.

Physics of defects in metal halide perovskites

Metal halide perovskites are widely used in optoelectronic devices, including solar cells, photodetectors, and light-emitting diodes. Defects in this class of low-temperature solution-processed semiconductors play significant roles in the optoelectronic properties and performance of devices based on these semiconductors. Investigating the defect properties provides not only insight into the origin of the outstanding performance of perovskite optoelectronic devices but also guidance for further improvement of performance. Defects in perovskites have been intensely studied. Here, we review the progress in defect-related physics and techniques for perovskites. We survey the theoretical and computational results of the origin and properties of defects in perovskites. The underlying mechanisms, functions, advantages, and limitations of trap state characterization techniques are discussed. We introduce the effect of defects on the performance of perovskite optoelectronic devices, followed by a discussion of the mechanism of defect treatment. Finally, we summarize and present key challenges and opportunities of defects and their role in the further development of perovskite optoelectronic devices.