Lingbo Xu

Enhanced performance and light soaking stability of planar perovskite solar cells using an amine-based fullerene interfacial modifier

Organic–inorganic lead halide perovskite solar cells (PSCs) with TiO2-based architectures have emerged for highly efficient photovoltaic conversion in recent years, while their serious light soaking instability limits their practical applications. Here, we have successfully introduced fullerene [6,6]-phenyl-C61-butyric acid 2-((2-(dimethylamino)ethyl)(methyl)-amino)-ethyl ester (PCBDAN) as an interfacial modifier for the TiO2 electron transport layer (ETL) in planar PSCs, which can significantly improve the photovoltaic conversion efficiency and light soaking stability of the devices. The quality of the perovskite film and electron extraction efficiency between the perovskite and ETL are both improved by introducing the PCBDAN interfacial layer. An improved power conversion efficiency (PCE) of 16.78% can be obtained for the device with PCBDAN under AM 1.5G illumination (100 mW cm−2). And the light soaking stability of the planar device is greatly improved after modification. This work provides a feasible way by interfacial modification for the realization of highly efficient devices without light-soaking degradation.

Enhanced Electronic Properties of SnO2 via Electron Transfer from Graphene Quantum Dots for Efficient Perovskite Solar Cells

Tin dioxide (SnO2) has been demonstrated as an effective electron-transporting layer (ETL) for attaining high-performance perovskite solar cells (PSCs). However, the numerous trap states in low-temperature solution processed SnO2 will reduce the PSCs performance and result in serious hysteresis. Here, we report a strategy to improve the electronic properties in SnO2 through a facile treatment of the films with adding a small amount of graphene quantum dots (GQDs). We demonstrate that the photogenerated electrons in GQDs can transfer to the conduction band of SnO2. The transferred electrons from the GQDs will effectively fill the electron traps as well as improve the conductivity of SnO2, which is beneficial for improving the electron extraction efficiency and reducing the recombination at the ETLs/perovskite interface. The device fabricated with SnO2:GQDs could reach an average power conversion efficiency (PCE) of 19.2 ± 1.0% and a highest steady-state PCE of 20.23% with very little hysteresis. Our study provides an effective way to enhance the performance of perovskite solar cells through improving the electronic properties of SnO2.

Self-Organized Fullerene Interfacial Layer for Efficient and Low-Temperature Processed Planar Perovskite Solar Cells with High UV-Light Stability

In this Communication, a self‐organization method of [6,6]‐phenyl‐C61‐butyric acid 2‐((2‐(dimethylamino)‐ethyl) (methyl)amino)ethyl ester (PCBDAN) interlayer in between 6,6‐phenyl C61‐butyric acid methyl ester (PCBM) and indium tin oxide (ITO) has been proposed to improve the performance of N–I–P perovskite solar cells (PSCs). The introduction of self‐organized PCBDAN interlayer can effectively reduce the work function of ITO and therefore eliminate the interface barrier between electron transport layer and electrode. It is beneficial for enhancing the charge extraction and decreasing the recombination loss at the interface. By employing this strategy, a highest power conversion efficiency of 18.1% has been obtained with almost free hysteresis. Furthermore, the N–I–P PSCs have excellent stability under UV‐light soaking, which can maintain 85% of its original highest value after 240 h accelerated UV aging. This self‐organization method for the formation of interlayer can not only simplify the fabrication process of low‐cost PSCs, but also be compatible with the roll‐to‐roll device processing on flexible substrates.

Silver nanoparticles modified reduced graphene oxide wrapped Ag3PO4/TiO2 visible-light-active photocatalysts with superior performance

Silver nanoparticles (Ag NPs) modified reduced graphene oxide wrapped Ag3PO4/TiO2 (Ag3PO4/TiO2/Ag-rGO, Ag-ATG) photocatalysts have been developed through a rational design that combines the optimization of charge generation, separation and transfer in the composites, which helps to increase the photocatalytic performance. The Ag-ATG composites possess novel microstructure, in which TiO2 mesoporous spheres of hundreds of nanometers in size are decorated with dense nano-sized Ag3PO4 to form pinecone-liked Ag3PO4/TiO2 particles, which were further wrapped by rGO sheets that are selectively decorated with Ag NPs. The Ag-ATG composites exhibit improved photocatalytic performance toward degradation of methylene blue (MB) and methyl orange (MO) under visible light compared to bare Ag3PO4 and Ag3PO4/TiO2/rGO (ATG). The underlying mechanism has been studied based on the results of reactive oxygen species capture experiment, photoluminescence (PL) spectra, and photocurrent measurements under visible light and monochromatic lights. The improved photocatalytic performance is mainly ascribed to the efficient spatial separation of photo-induced electrons and holes in Ag-ATG, i.e., the electrons in Ag3PO4 transfer to Ag-rGO, meanwhile the holes in Ag3PO4 transfer to TiO2. Ag NPs play an important role in the hybrid structure owing to the synergistic effect of Ag NPs and rGO, which not only enhance the light harvest but also increase the capacity of electron accepting from Ag3PO4. Meanwhile, active photo-induced electrons at the plasmonic Ag NPs can facilitate the formation of O2˙− radicals for photocatalysis. As a result, both the stability and photocatalytic active of Ag-ATG are significantly improved.

Amine treatment induced perovskite nanowire network in perovskite solar cells: efficient surface passivation and carrier transport

In the fabrication of high efficiency organic-inorganic metal halide perovskite solar cells (PSCs), an additional interface modifier is usually applied for enhancing the interface passivation and carrier transport. In this paper, we develop an innovative method with in-situ growth of one-dimensional perovskite nanowire (1D PNW) network triggered by Lewis amine over the perovskite films. To our knowledge, this is the first time to fabricate PSCs with shape-controlled perovskite surface morphology, which improved power conversion efficiency (PCE) from 14.32% to 16.66% with negligible hysteresis. The amine molecule can passivate the trap states on the polycrystalline perovskite surface to reduce trap-state density. Meanwhile, as a fast channel, the 1D PNWs would promote carrier transport from the bulk perovskite film to the electron transport layer. The PSCs with 1D PNW modification not only exhibit excellent photovoltaic performances, but also show good stability with only 4% PCE loss within 30 days in the ambient air without encapsulation. Our results strongly suggest that in-situ grown 1D PNW network provides a feasible and effective strategy for nanostructured optoelectronic devices such as PSCs to achieve superior performances.

Surface plasmon enhanced luminescence from organic-inorganic hybrid perovskites

The authors observe more than six-fold enhancement of emission from CH3NH3PbI3 by employing surface plasmon (SP) in Au films. The enhancement mainly results from the increased radiative recombination rate via SP-coupling, with a small contribution from the back-reflection of Au. The SP-coupling technique is found to be more effective for CH3NH3PbI3 with relatively low quantum efficiency. This property leads to the homogeneous luminescence from inhomogeneous CH3NH3PbI3 samples. The SP-coupling technique thus provides a promising solution for super bright, high-speed, and large-area perovskite-based light emitting devices.

Enhanced optoelectronic quality of perovskite films with excess CH3NH3I for high-efficiency solar cells in ambient air

Solution-processed polycrystalline perovskite films contribute critically to the high photovoltaic performance of perovskite-based solar cells (PSCs). The inevitable electronic trap states at grain boundaries and intrinsic defects such as metallic lead (Pb0) and halide vacancies in perovskite films cause serious carrier recombination loss. Furthermore, the film can easily decompose into PbI2 in a moist atmosphere. Here, we introduce a simple strategy, through a small increase in methylammonium iodide (CH3NH3I, MAI), molar proportion (5%), for perovskite fabrication in ambient air with ∼50% relative humidity. Analysis of the morphology and crystallography demonstrates that excess MAI significantly promotes grain growth without decomposition. X-ray photoemission spectroscopy shows that no metallic Pb0 exists in the perovskite film and the I/Pb ratio is improved. A time-resolved photoluminescence measurement indicates efficient suppression of non-radiative recombination in the perovskite layer. As a result, the device yields improved power conversion efficiency from 14.06% to 18.26% with reduced hysteresis and higher stability under AM1.5G illumination (100 mW cm-2). This work strongly provides a feasible and low-cost way to develop highly efficient PSCs in ambient air.

CH3NH3PbBr3 Quantum Dot-Induced Nucleation for High Performance Perovskite Light-Emitting Solar Cells

Solution-processed organometallic halide perovskites have obtained rapid development for light-emitting diodes (LEDs) and solar cells (SCs). These devices are fabricated with similar materials and architectures, leading to the emergence of perovskite-based light-emitting solar cells (LESCs). The high quality perovskite layer with reduced nonradiative recombination is crucial for achieving a high performance device, even though the carrier behaviors are fundamentally different in both functions. Here CH3NH3PbBr3 quantum dots (QDs) are first introduced into the antisolvent in solution phase, serving as nucleation centers and inducing the growth of CH3NH3PbI3 films. The heterogeneous nucleation based on high lattice matching and a low free-energy barrier significantly improves the crystallinity of CH3NH3PbI3 films with decreased grain sizes, resulting in longer carrier lifetime and lower trap-state density in the films. Therefore, the LESCs based on the CH3NH3PbI3 films with reduced recombination exhibit improved electroluminescence and external quantum efficiency. The current efficiency is enhanced by 1 order of magnitude as LEDs, and meanwhile the power conversion efficiency increases from 14.49% to 17.10% as SCs, compared to the reference device without QDs. Our study provides a feasible method to grow high quality perovskite films for high performance optoelectronic devices.