Ethylamine Iodide Additive Enables Solid-to-Solid Transformed Highly Oriented Perovskite for Excellent Photodetectors

Self-Powered MAPbI3 Heterojunction Photodetector with Gradient-Level Electron Transport Layers and Dual Pyro-Phototronic Effects

An electron transport layer (ETL) with a suitable gradient energy level can enhance electron transfer, suppress carrier recombination, and effectively improve the photoresponse of photodetectors (PDs). In this letter, a series of ITO/ZnO/CdS/MAPbI3/Spiro-OMeTAD heterojunction PDs were prepared by incorporating a ZnO layer at the CdS/ITO interface upon varying the thickness from 0 to 95 nm. The optimized band arrangement in the PD results in an excellent self-powering ability and improved photoresponse. Moreover, both the photovoltaic and pyroelectric responses strongly correlate with the thickness of the ZnO layer. The PD with an optimal ZnO thin film thickness of 50 nm achieves a huge responsivity (R) of 1.19 × 104 V/W and detectivity (D) of 2.22 × 109 Jones, primarily due to the strengthened pyro-phototronic effects enabled by the dual ETL layers. In addition, the enhanced pyroelectric effect broadens the spectral range of the PD to 360-1550 nm, largely surpassing the band gap of the heterojunction.

Synergistic nucleation regulation using 4,4',4''-tris(carbazol-9-yl)-triphenylamine and moisture for stably air-processed high-performance perovskite photodetectors

Perovskite photodetectors (PPDs) offer a promising solution with low cost and high responsivity, addressing the limitations of traditional inorganic photodetectors. However, there is still room for improvement in terms of the dark current and stability of air-processed PPDs. In this study, 4,4',4''-tris(carbazol-9-yl)-triphenylamine (TCTA) was utilized as a nucleation agent to enhance the quality of perovskite films. The synergistic effect of TCTA and moisture promotes rapid nucleation of PbI2-PbCl2, resulting in an increased nucleation rate and the elimination of pinholes in the film. By employing additive engineering, we obtained a PbI2-PbCl2 layer with high coverage, leading to a low density of traps in the corresponding perovskite film. Consequently, the modified PPD exhibits a remarkable reduction in dark current density by over one order of magnitude, reaching 2.4 × 10-10 A cm-2 at -10 mV, along with a large linear dynamic range (LDR) of 183 dB. Furthermore, the resulting PPD demonstrates remarkable stability, retaining 90% of the initial external quantum efficiency (EQE) value even after continuous operation for over 3200 hours. Owing to a fast response time in the nanosecond range, the PPD could convert modulated light signals into electrical signals at a speed of 588 Kbit s-1, highlighting the great potential in the field of optical communication.

Uracil Induced Simultaneously Strengthening Grain Boundaries and Interfaces Enables High-Performance Perovskite Solar Cells with Superior Operational Stability

The operational stability is a huge obstacle to further commercialization of perovskite solar cells. To address this critical issue, in this work, uracil is introduced as a "binder" into the perovskite film to simultaneously improve the power conversion efficiency (PCE) and operational stability. Uracil can efficiently passivate defects and strengthen grain boundaries to enhance the stability of perovskite films. Moreover, the uracil also strengthens the interface between the perovskite and the Tin oxide (SnO2 ) electron transport layer to increase the binding force. The uracil-modified devices deliver a champion PCE of 24.23% (certificated 23.19%) with negligible hysteresis at active area of 0.0625 cm2 . In particular, the optimal device exhibits over 90% of its initial PCE after tracking for ≈6000 h at its maximum power point under continuous light, indicating its superior operational stability. Moreover, the devices also show great reproducibility in both PCE and operational stability.

Recent progress of crystal orientation engineering in halide perovskite photovoltaics

Manipulating the crystallographic orientation of semiconductor crystals plays a vital role in fine-tuning their facet-dependent properties, such as surface properties, charge transfer properties, trap state density, and lattice strain. The success in crystal orientation engineering enables the preferential growth orientation of perovskite thin films with favorable crystal planes by precise nucleation manipulation and growth condition optimization, rendering the films with the unique optoelectronic properties to further improve the efficiency of perovskite solar cells (PSCs). However, the origin and impact of preferential crystallographic orientation of perovskite thin films on the corresponding photovoltaic performance of PSCs are still far from being well understood. Herein, we explore the crystal orientation-dependent optoelectronic properties of halide perovskites and their influence on the photovoltaic performance of PSCs. We summarize the basic strategies for crystal facet engineering in the fabrication of preferentially oriented perovskite thin films, with a focus on the oriented growth mechanism during thin film formation. Based on the above knowledge and the recent research progress in terms of crystal orientation engineering in PSCs, a brief outlook on the remaining challenges and perspectives are provided.

Phase-Transition-Cycle-Induced Recrystallization of FAPbI3 Film in An Open Environment Toward Excellent Photodetectors with High Reproducibility

Perovskite is an attractive building block for future optoelectronic applications. However, the strict fabrication conditions of perovskite devices impede the transformation of lab techniques into commercial applications. Here, a facile annealing-free posttreatment is proposed to reconstruct the perovskite film to obtain high-performance photodetectors with an optimized production rate. With posttreatment by methylamine thiocyanate, the prefabricated formamidinium-lead triiodide (FAPbI₃ ) film will undergo a recrystallization process consisting of a repeating phase-transition-cycle (PTC) between the black and yellow phases of FAPbI₃ , which improves the crystal quality and eliminates defects. As a result, some casually prepared or even decomposed perovskite films can be reconstructed, and the dispersion degree of the device performance based on the posttreatment method decreases by ≈21% compared to the traditional antisolvent method. This facile and annealing-free posttreatment will be an attractive method for the future industrial production of perovskite devices.

N -(2-aminoethyl) Acetamide Additive Enables Phase-Pure and Stable α-FAPbI3 for Efficient Self-Powered Photodetectors

Formamidinium-lead triiodide (FAPbI₃ ) perovskite is considered as one of the most promising perovskite materials for high-performance photodetectors because of its narrow bandgap and superior thermal stability. Nevertheless, to realize efficient carrier transport and highly performing photodetectors, it imposes the requirement of fabricating α-FAPbI₃ with pure phase, preferred crystal orientation, large grain size, and passivated interface, which still remains challenging. Here, a facile strategy based on additive engineering to obtain pure-phase FAPbI₃ perovskite films by introducing N-(2-aminoethyl) acetamide into perovskite precursors is reported. The formation of chemical bond and hydrogen bond between N-(2-aminoethyl) acetamide and perovskite reduces the potential barrier in the phase-transition process from an intermediate yellow phase to a final black phase, passivates the defects of the film, and leads to a high-quality and phase-pure α-FAPbI₃ perovskite. A self-powered photodetector based on the as-fabricated FAPbI₃ film exhibits a maximum responsivity of 0.48 A W^-1 at 700 nm with a peak external quantum efficiency of 95% at 440 nm. Moreover, the optimized device remains 83% of the initial performance after 576 h storage at ambient condition. This work provides a simple and feasible scheme for the preparation of high-quality phase-pure α-FAPbI₃ perovskite and associated devices.

Low-Temperature Phase-Transition for Compositional-Pure α-FAPbI3 Solar Cells with Low Residual-Stress and High Crystal-Orientation

Transition of δ-phase formamidinium lead triiodide (δ-FAPbI₃ ) to pure α-phase FAPbI₃ (α-FAPbI₃ ) typically requires high processing temperature (150 °C), which often results in unavoidable residual stress. Besides, using methylammonium chloride (MACl) as additive in fabrication will cause MA residue in the film, compromising the compositional purity. Here, a stress-released and compositional-pure α-FAPbI₃ thin-film is fabricated using 3-chloropropylammonium chloride (Cl-PACl) by two-step annealing. The 2D template of n = 2 can preferentially form in perovskite with the introduction of Cl-PACl at a temperature as low as 80 °C. Such a 2D template can guide the free components to form ordered α-FAPbI₃ and promote the transition of the formed δ-FAPbI₃ to α-FAPbI₃ by reducing the phase transition energy. As a result, the obtained perovskite films via low-temperature phase-transition have a high degree of crystal orientation and reduced residual stress. More importantly, most of the Cl-PACl is volatilized during the subsequent high-temperature annealing process accompanied by the disintegration of the 2D templates. The residual trace of Cl-PA⁺ is mainly concentrated at the grain boundary near the perovskite surface layer, stabilizing α-FAPbI₃ and passivating defects. Perovskite solar cell based on pure α-FAPbI₃ achieves a power conversion efficiency of 23.03% with excellent phase stability and photo-stability.