Tin-Lead Perovskite Solar Cells with Preferred Crystal Orientation by Buried Interface Approach.

Mixed tin-lead perovskite solar cells (PSCs) have garnered much attention for their ideal bandgap and high environmental research value. However, poly (3,4-ethylenedioxythiophene): poly (styrene sulfonate) (PEDOT: PSS), widely used as a hole transport layer (HTL) for Sn-Pb PSCs, results in unsatisfactory power conversion efficiency (PCE) and long-term stability of PSCs due to its acidity and moisture absorption. A synergistic strategy by incorporating histidine (HIS) into the PEDOT: PSS HTL is applied to simultaneously regulate the nucleation and crystallization of perovskite (PVK). HIS neutralizes the acidity of PEDOT: PSS and enhances conductivity. Especially, the coordination of the C═N and -COO- functional groups in the HIS molecule with Sn2+ and Pb2+ induces vertical growth of PVK film, resulting in the release of residual surface stress. Additionally, this strategy also optimizes the energy level alignment between the perovskite layer and the HTL, which improves charge extraction and transport. With these cooperative effects, the PCE of Sn-Pb PSCs reaches 21.46% (1 sun, AM1.5), maintaining excellent stability under a nitrogen atmosphere. Hence, the buried interface approach exhibits the potential for achieving high-performance and stable Sn-Pb PSCs.

Urea additive improves the performance of low bandgap tin-lead perovskite solar cells.

Recently, narrow bandgap tin-lead mixed perovskite solar cells (PSCs) have become a research hotspot because they can be applied in tandem cells to break the Shockley-Queisser radiative limit of the single junction PSCs. However, the introduction of tin, on the one hand, makes the crystal quality of perovskite thin film worse, leading to the increase of film defects; on the other hand, the easy oxidation of divalent tin also leads to the increase of defect states, which seriously affects the photoelectric conversion efficiency of tin-lead cell devices. Good crystallization and low defect density of perovskite layer are very important to ensure good light absorption and photogenerated carrier generation and transport. Here, we adjust the crystallization of tin-lead perovskite films by a Lewis base-urea (CO(NH2)2), which significantly increases the grain size and improves the film morphology. At the same time, because of the Lewis base property of urea, the uncoordinated Pb2+and Sn2+defects of Lewis acids in the tin-lead films are effectively passivated, and the occurrence of non-radiative recombination in the films is reduced. Under the dual effects of improving crystallization and passivating defects, the photoelectric performance of tin-lead perovskite solar cell devices is significantly improved to 18.1% compared with the original device of 15.4%.

Reductive Sn2+ Compensator for Efficient and Stable Sn-Pb Mixed Perovskite Solar Cells.

Tin-lead (Sn-Pb) mixed perovskite with a narrow bandgap is an ideal candidate for single-junction solar cells approaching the Shockley-Queisser limit. However, due to the easy oxidation of Sn2+, the efficiency and stability of Sn-Pb mixed perovskite solar cells (PSCs) still lag far behind that of Pb-based solar cells. Herein, highly efficient and stable FA0.5MA0.5Pb0.5Sn0.5I0.47Br0.03 compositional PSCs are achieved by introducing an appropriate amount of multifunctional Tin (II) oxalate (SnC2O4). SnC2O4 with compensative Sn2+ and reductive oxalate group C2O4 2- effectively passivates the cation and anion defects simultaneously, thereby leading to more n-type perovskite films. Benefitting from the energy level alignment and the suppression of bulk nonradiative recombination, the Sn-Pb mixed perovskite solar cell treated with SnC2O4 achieves a power conversion efficiency of 21.43%. More importantly, chemically reductive C2O4 2- effectively suppresses the notorious oxidation of Sn2+, leading to significant enhancement in stability. Particularly, it dramatically improves light stability.

Efficient Air-Processed MA-Free Perovskite Solar Cells by SH-Based Silane Interface Modification.

Air-processed perovskite solar cells (PSCs) with high photoelectric conversion efficiency (PCE) can not only further reduce the production cost but also promote its industrialization. During the preparation of the PSCs in ambient air, the contact of the buried interface not only affects the crystallization of the perovskite film but also affects the interface carrier transport, which is directly related to the performance of the device. Here, we optimize the buried interface by introducing 3-mercaptopropyltrimethoxysilane (MPTMS, (CH3O)3Si(CH2)3SH) on the nickel oxide (NiOx) surface. The crystallization of the perovskite film is improved by enhancing surface hydrophobicity; besides, the SH-based functional group of MPTMS passivates the uncoordinated lead at the interface, which effectively reduces the defects at the bottom interface of perovskite and inhibits the nonradiative recombination at the interface. Moreover, the energy level between the NiOx layer and the perovskite layer is better matched. Based on multiple functions of MPTMS modification, the open circuit voltage of the device is obviously improved, and efficient air-processed methylamine-free (MA-free) PSCs are realized with PCE reaching 21.0%. The device still maintains the initial PCE of 85% after 1000 h aging in the glovebox. This work highlights interface modification in air-processed MA-free PSCs to promote the industrialization of PSCs.

Pb and Li co-doped NiOx for efficient inverted planar perovskite solar cells.

Organic-inorganic halide perovskites solar cells have garnered increasing attention in recent years due to the dramatic rise in power conversion efficiencies (PCEs). In perovskite solar cells (PSCs), selecting appropriate hole transport materials to insert between perovskite layer and electrodes can improve Schottky contact, facilitate the hole transport, therefore reduce charge recombination, and therefore improve cell performance. Doping of metal cation is an effective means to regulate energy level structure and change its conductivity. In this study, we novelly introduce the Pb2+ doped NiOx as the hole transport materials to decrease the energy loss between NiOx and the perovskite layer, which improves open-circuit voltage (Voc) of the PSCs. In order to improve the conductivity of the NiOx film, the Li+ co-doping is introduced. We introduce Pb and Li co-doping strategy to match the work function of doped NiOx with perovskite valence band energy level, and increase the conductivity of NiOx for high-efficiency inverted planar PSCs. The Pb and Li co-doped NiOx devices exhibit efficient hole extraction and enhanced conductivity, which improve the performance of inverted planar PSCs to 17.02% compared with 15.40% of the undoped device.

Graphite-N Doped Graphene Quantum Dots as Semiconductor Additive in Perovskite Solar Cells.

Efficient charge transport is especially important for achieving high performance of perovskite solar cells (PSCs). Here, molecularly designed graphite-nitrogen doped graphene quantum dots (GN-GQDs) act as a functional semiconductor additive in perovskite film. GN-GQDs with abundant N active sites participate in the crystallization of perovskite film and effectively passivate the grain boundary (GB) trap states by Lewis base/acid interaction. Moreover, the semiconductive GN-GQDs at GBs exhibit matched energy structure with the perovskite, which facilitate the charge transport at GBs. GN-GQDs also show n-type dopant property to upshift the Fermi energy level of perovskite films. It largely improves the charge transport in PSCs and reduces the interface recombination at the same time. Profiting from these advantages, inverted planar PSCs with NiO/perovskite/PCBM/BCP structure achieves high efficiency of 19.8% with no hysteresis phenomenon. GN-GQDs modified PSCs also show high stability even without encapsulation, benefiting from the protected GBs and more hydrophobic surface of the modified film. This work highlights a judicious design method of GQDs additive to satisfy efficient and stable PSCs.