Enhancing Stability and Efficiency of Inverted Inorganic Perovskite Solar Cells with In-Situ Interfacial Cross-Linked Modifier.

Inverted inorganic perovskite solar cells (PSCs) is potential as the top cells in tandem configurations, owing to the ideal bandgap, good thermal and light stability of inorganic perovskites. However, challenges such as mismatch of energy levels between charge transport layer and perovskite, significant non-radiative recombination caused by surface defects, and poor water stability have led to the urgent need for further improvement in the performance of inverted inorganic PSCs. Herein, the fabrication of efficient and stable CsPbI3-xBrx PSCs through surface treatment of (3-mercaptopropyl) trimethoxysilane (MPTS), is reported. The silane groups in MPTS can in situ crosslink in the presence of moisture to build a 3-dimensional (3D) network by Si-O-Si bonds, which forms a hydrophobic layer on perovskite surface to inhibit water invasion. Additionally, -SH can strongly interact with the undercoordinated Pb2+ at the perovskite surface, effectively minimizing interfacial charge recombination. Consequently, the efficiency of the inverted inorganic PSCs improves dramatically from 19.0% to 21.0% under 100 mW cm-2 illumination with MPTS treatment. Remarkably, perovskite films with crosslinked MPTS exhibit superior stability when soaking in water. The optimized PSC maintains 91% of its initial efficiency after aging 1000 h in ambient atmosphere, and 86% in 800 h of operational stability testing.

Defect Passivation and Lithium Ion Coordination Via Hole Transporting Layer Modification for High Performance Inorganic Perovskite Solar Cells.

Metal halide inorganic perovskite solar cells (PSCs) have great potential to achieve high efficiency with excellent thermal stability. However, the surface defect traps restrain the achievement of high open circuit voltage (VOC ) and power conversion efficiency (PCE) of the devices due to the severe nonradiative charge recombination. Moreover, the state-of-the-art hole transporting layer (HTL) significantly hampers device moisture stability, even though it renders the highest solar cell efficiency. Herein, a one-stone-two-birds strategy is proposed using a biocompatible material tryptamine (TA) as an additive in HTL. First, TA bearing electron rich moieties can favorably passivate the surface defects of inorganic perovskite films, significantly reducing trap density and prolonging charge lifetime. It results in a drastic improvement of VOC from 1.192 to 1.251 V, with a VOC loss of 0.48 V. The corresponding PSCs achieve a 21.8% PCE under 100 mW cm-2 illumination. Second, TA in HTL can coordinate with lithium cations, retarding their reaction with moisture and increasing the moisture stability of HTL. Consequently, the black phase of inorganic perovskite films is well preserved, and the corresponding PSCs maintain 90% of the initial PCE after 800 h storage at relative humidity of 25-35%, much higher than the control devices.

Strengthened Surface Modification for High-Performance Inorganic Perovskite Solar Cells with 21.3% Efficiency.

Metal halide inorganic perovskites show excellent thermal stability compared to organic-inorganic perovskites. However, the performance of inorganic perovskite solar cells (PSCs) is far from theoretical values, together with unsatisfactory stability, mainly due to the poor interfacial properties. In this work, a facial but effective method is reported to realize high-performance inorganic PSCs by post-modifying the perovskite surface with 2-thiophene ethylamine (TEA). It is found that amine group from TEA can favorably interact with the undercoordinated Pb2+ via Lewis acid-based coordination, while thiophene ring with electron-rich sulfur assists such interaction by functioning as an electron donor. The synergetic interaction allows TEA to passivate perovskite film defects more efficiently, as compared to phenethylamine (PEA) with less electron-donating ability. Moreover, perovskite valence band is slightly upward shift to match with hole transport material and facilitate hole transfer. These combinations result in a reduced non-radiative charge recombination and improved charge carrier lifetime. Consequently, PSCs with TEA modification shows a drastic improvement of VOC by 54 mV, yielding a champion PCE of 21.3%, much higher than the control PSCs (19.3%), along with improved ambient stability. This work demonstrates that surface modifier with an electron-rich moiety is critical for achieving efficient and stable inorganic PSCs.

Interface Modification for Efficient and Stable Inverted Inorganic Perovskite Solar Cells.

Due to their excellent thermal stability and ideal bandgap, metal halide inorganic perovskite based solar cells (PSCs) with inverted structure are considered as an excellent choice for perovskite/silicon tandem solar cells. However, the power conversion efficiency (PCE) of inverted inorganic perovskite solar cells (PSCs) still lags far behind that of conventional n-i-p PSCs due to interfacial energy level mismatch and high nonradiative charge recombination. Herein, the performance of inverted PSCs is significantly improved by interfacial engineering of CsPbI3- x Brx films with 2-mercapto-1-methylimidazole (MMI). It is found that the mercapto group can preferably react with the undercoordinated Pb2+ from perovskite by forming Pb-S bonds, which appreciably reduces the surface trap density. Moreover, MMI modification results in a better energy level alignment with the electron-transporting material, promoting carrier transfer and reducing voltage deficit. The above combination results in an open-circuit voltage enhancement by 120 mV, yielding a champion PCE of 20.6% for 0.09 cm2 area and 17.3% for 1 cm2 area. Furthermore, the ambient, operational and heat stabilities of inorganic PSCs with MMI modification are also greatly improved. The work demonstrates a simple but effective approach for fabricating highly efficient and stable inverted inorganic PSCs.

Simultaneous Lattice Engineering and Defect Control via Cadmium Incorporation for High-Performance Inorganic Perovskite Solar Cells.

Doping of all-inorganic lead halide perovskites to enhance their photovoltaic performance and stability has been reported to be effective. Up to now most studies have focused on the doping of elements in to the perovskite lattice. However, most of them cannot be doped into the perovskite lattice and the roles of these dopants are still controversial. Herein,the authors introduce CdI2 as an additive into CsPbI3-x Brx and use it as active layer to fabricate high-performance inorganic perovskite solar cells (PSCs). Cd with a smaller radius than Pb can partially substitute Pb in the perovskite lattice by up to 2 mol%. Meanwhile, the remaining Cd stays on the surface and grain boundaries (GB) of the perovskite film in the form of Cs2 CdI4-x Br-x , which is found to reduce non-radiative recombination. These effects result in prolonged charge carrier lifetime, suppressed defect formation, decreased GBs, and an upward shift of energybands in the Cd-containing film. A champion efficiency of 20.8% is achieved for Cd-incorporated PSCs, together with improved device ambient stability. This work highlights the importance of simultaneous lattice engineering, defectcontrol and atomic-level characterization in achieving high-performance inorganic PSCs with well-defined structure-property relationships.