Showing papers by "Anyi Mei published in 2017"

Stable Large-Area (10 × 10 cm2) Printable Mesoscopic Perovskite Module Exceeding 10% Efficiency

Abstract: The commercial manufacturing of perovskite solar modules (PSM) suffers from stability concerns and scalability issues. We demonstrate a hole-conductor-free printable solar module embodiment, which employs a triple layer of mesoporous TiO2/ZrO2/carbon as scaffold, and is infiltrated by a mixed cation lead halide perovskite (5-AVA)x(MA)1−xPbI3 as a light harvester. Here, hole conductor or Au reflector are not employed, and instead, the back contact comprises simply a printed carbon layer. Upon optimizing the thickness alignment of the triple mesoscopic layer and the design of the active area, the unit cell shows 14.02% power conversion efficiency (PCE) under 100 mW cm−2 condition, while a larger area of 10 serially connected cells module (10 × 10 cm2), shows a 10.4% PCE on an active area of 49 cm2. Light-soaking stability of 1000 h has been demonstrated, as well as local outdoor stability of 1 month and a shelf-life stability of over 1 year. This paves the way for the realization of efficient and stable large-area PSMs for industrial deployment.

Synergy of ammonium chloride and moisture on perovskite crystallization for efficient printable mesoscopic solar cells.

Abstract: Organometal lead halide perovskites have been widely used as the light harvester for high-performance solar cells. However, typical perovskites of methylammonium lead halides (CH3NH3PbX3, X=Cl, Br, I) are usually sensitive to moisture in ambient air, and thus require an inert atmosphere to process. Here we demonstrate a moisture-induced transformation of perovskite crystals in a triple-layer scaffold of TiO2/ZrO2/Carbon to fabricate printable mesoscopic solar cells. An additive of ammonium chloride (NH4Cl) is employed to assist the crystallization of perovskite, wherein the formation and transition of intermediate CH3NH3X·NH4PbX3(H2O)2 (X=I or Cl) enables high-quality perovskite CH3NH3PbI3 crystals with preferential growth orientation. Correspondingly, the intrinsic perovskite devices based on CH3NH3PbI3 achieve an efficiency of 15.6% and a lifetime of over 130 days in ambient condition with 30% relative humidity. This ambient-processed printable perovskite solar cell provides a promising prospect for mass production, and will promote the development of perovskite-based photovoltaics.

Tunable hysteresis effect for perovskite solar cells

Abstract: Perovskite solar cells (PSCs) usually suffer from a hysteresis effect in current–voltage measurements, which leads to an inaccurate estimation of the device efficiency. Although ion migration, charge trapping/detrapping, and accumulation have been proposed as a basis for the hysteresis, the origin of the hysteresis has not been apparently unraveled. Herein we reported a tunable hysteresis effect based uniquely on open-circuit voltage variations in printable mesoscopic PSCs with a simplified triple-layer TiO2/ZrO2/carbon architecture. The electrons are collected by the compact TiO2/mesoporous TiO2 (c-TiO2/mp-TiO2) bilayer, and the holes are collected by the carbon layer. By adjusting the spray deposition cycles for the c-TiO2 layer and UV-ozone treatment, we achieved hysteresis-normal, hysteresis-free, and hysteresis-inverted PSCs. Such unique trends of tunable hysteresis are analyzed by considering the polarization of the TiO2/perovskite interface, which can accumulate positive charges reversibly. Successfully tuning of the hysteresis effect clarifies the critical importance of the c-TiO2/perovskite interface in controlling the hysteretic trends observed, providing important insights towards the understanding of this rapidly developing photovoltaic technology.

Effect of guanidinium on mesoscopic perovskite solar cells

Abstract: Hole-conductor-free printable mesoscopic perovskite solar cells based on a TiO2/ZrO2/carbon architecture have attracted much attention due to their low material cost and simple fabrication process. However, the micron-thick mesoporous scaffold always challenges the filling of the perovskite absorber and causes significant charge carrier loss. We employ a multifunctional additive of guanidinium chloride (GuCl) to improve the quality of the CH3NH3PbI3 perovskite absorber, and suppress the recombination reaction in the device. It is found that GuCl effectively enhances the charge carrier lifetimes of the perovskite, and suppresses charge carrier loss in the hole-conductor-free devices. Correspondingly, the open-circuit voltage (VOC) of the device is significantly enhanced from 0.88 V to 1.02 V.

Improvement and Regeneration of Perovskite Solar Cells via Methylamine Gas Post-Treatment

Abstract: The control of film morphology is crucial in achieving high-performance perovskite solar cells (PSCs). Herein, the crystals of the perovskite films are reconstructed by post-treating the MAPbI3 devices with methylamine gas, yielding a homogeneous nucleation and crystallization of the perovskite in the triple mesoscopic inorganic layers structured PSCs. As a result, a uniform, compact, and crystalline perovskite layer is obtained after the methylamine gas post-treatment, yielding high power conversion efficiency (PCE) of 15.26%, 128.8% higher than that of the device before processing. More importantly, this post-treatment process allows the regeneration of the photodegraded PSCs via the crystal reconstruction and the PCE can recover to 91% of the initial value after two cycles of the photodegradation-recovery process. This simple method allows for the regeneration of perovskite solar cells on site without reconstruction or replacing any components, thus prolonging the service life of the perovskite solar cells and distinguishing from any other photovoltaic devices in practice.

Boron-Doped Graphite for High Work Function Carbon Electrode in Printable Hole-Conductor-Free Mesoscopic Perovskite Solar Cells.

Abstract: Work function of carbon electrodes is critical in obtaining high open-circuit voltage as well as high device performance for carbon based perovskite solar cells. Herein, we propose a novel strategy to upshift work function of carbon electrode by incorporating boron atom into graphite lattice and em-ploy it in printable hole-conductor-free mesoscopic perovskite solar cells. The high-work-function boron-doped carbon electrode facilitates hole extraction from perovskite as verified by photoluminescence. Meanwhile, the carbon electrode is endowed with an improved conductivity due to a higher graphitization carbon of boron-doped graphite. These advantages of the boron-doped carbon electrode result in a low charge transfer resistance at carbon/perovskite interface and an extended carrier re-combination lifetime. Together with the merit of both high work function and conductivity, the power conversion efficiency of hole-conductor-free mesoscopic perovskite solar cells is increased from 12.4 % for the pristine nee...

Spacer improvement for efficient and fully printable mesoscopic perovskite solar cells

Abstract: Highly dispersible TiO2@ZrO2 nanoparticles are synthesized to prepare an ultra-flat and crack-free spacer film, leading to an enhanced insulating ability compared to a conventional spacer. The average power conversion efficiency of fully printable mesoscopic perovskite solar cells is improved from 10.2% to 12.5%, and the highest steady output power conversion efficiency is 13.8%.