Jiangsheng Xie

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.

Ambient Engineering for High-Performance Organic–Inorganic Perovskite Hybrid Solar Cells

Considering the evaporation of solvents during fabrication of perovskite films, the organic ambience will present a significant influence on the morphologies and properties of perovskite films. To clarify this issue, various ambiences of N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and chlorobenzene (CBZ) are introduced during fabrication of perovskite films by two-step sequential deposition method. The results reveal that an ambient CBZ atmosphere is favorable to control the nucleation and growth of CH3NH3PbI3 grains while the others present a negative effect. The statistical results show that the average efficiencies of perovskite solar cells processed in an ambient CBZ atmosphere can be significantly improved by a relatively average value of 35%, compared with those processed under air. The efficiency of the best perovskite solar cells can be improved from 10.65% to 14.55% by introducing this ambience engineering technology. The CH3NH3PbI3 film with large-size grains produced in an ambient CBZ atmosphere can effectively reduce the density of grain boundaries, and then the recombination centers for photoinduced carriers. Therefore, a higher short-circuit current density is achieved, which makes main contribution to the improvement in efficiency. These results provide vital progress toward understanding the role of ambience in the realization of highly efficient perovskite solar cells.

Fulleropyrrolidinium Iodide As an Efficient Electron Transport Layer for Air-Stable Planar Perovskite Solar Cells

Organic-inorganic halide perovskite solar cells have attracted great attention in recent years. But there are still a lot of unresolved issues related to the perovskite solar cells such as the phenomenon of anomalous hysteresis characteristics and long-term stability of the devices. Here, we developed a simple three-layered efficient perovskite device by replacing the commonly employed PCBM electrical transport layer with an ultrathin fulleropyrrolidinium iodide (C60-bis) in an inverted p-i-n architecture. The devices with an ultrathin C60-bis electronic transport layer yield an average power conversion efficiency of 13.5% and a maximum efficiency of 15.15%. Steady-state photoluminescence (PL) and time-resolved photoluminescence (TRPL) measurements show that the high performance is attributed to the efficient blocking of holes and high extraction efficiency of electrons by C60-bis, due to a favorable energy level alignment between the CH3NH3PbI3 and the Ag electrodes. The hysteresis effect and stability of our perovskite solar cells with C60-bis become better under indoor humidity conditions.

Room-temperature processed, air-stable and highly efficient graphene/silicon solar cells with an organic interlayer

Graphene/silicon (Gr/Si) solar cells have attracted interest for their potential in low-cost photovoltaic applications. Inserting a p-type organic hole transporting layer (HTL) in-between the Gr and Si would suppress carrier recombination and improve the performance of the solar cells. Here, we report highly stable and high-performance Gr/Si solar cells fabricated by using a room-temperature process. Spiro-OMeTAD was selected as the HTL for its novel electrical and optical properties. The employment of spiro-OMeTAD led to an impressive power conversion efficiency (PCE) of 13.02%. Moreover, our solar cells exhibit excellent stability with a PCE of ∼11% for over four months. These results could be encouraging for the development of Gr/Si solar cells toward practical applications. Meanwhile, this work offers a universal solution for the application of organics in Gr-based optoelectronics and photovoltaics from the viewpoint of device robustness.

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.

A ternary organic electron transport layer for efficient and photostable perovskite solar cells under full spectrum illumination

Perovskite solar cells using titanium dioxide (TiO2) for electron extraction have achieved high efficiency, but tend to degrade under full spectral illumination due to ultraviolet (UV) photocatalysis. PCBM might be an alternative candidate to overcome this instability issue, however, its PSC efficiency is still low due to relatively poor electrical conductivity and contact interface barriers with the electrode. Here, we demonstrate that the addition of C60 and self-organized PFN to PCBM as a ternary electron transport layer (ETL) can effectively improve the device performance by enhancing the conductivity and buffering the interfacial contact simultaneously. As a result, the highest hysteresis-free power conversion efficiency (PCE) of 19.31% has been achieved. Furthermore, the device based on ternary PCBM:C60:PFN can retain 91.3% of its initial PCE over 1056 hours of continuous full spectral illumination after a “burn in” period and thus shows a more stable performance than TiO2 based PSCs. This low-temperature (≤100 °C) prepared ternary material may offer the possibility of roll-to-roll mass production on flexible substrates and achieve highly photo-stable PSCs under full spectral illumination without the requirement of an additional UV filter.

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.