Chen Weijie

The long‐term photostability under AM1.5G simulated 1 sun illumination including UV is demonstrated with the perovskite solar cell exceeding power conversion efficiency of 20%. This achievement stems from understanding the role of oxygen on the degradation under illumination. Oxygen induces iodine migration from the perovskite to a hole transport layer, which interrupts the charge transport through the interface.

Abstract

Perovskite solar cells (PSCs) with mesoporous TiO₂ (mp‐TiO₂) as the electron transport material attain power conversion efficiencies (PCEs) above 22%; however, their poor long‐term stability is a critical issue that must be resolved for commercialization. Herein, it is demonstrated that the long‐term operational stability of mp‐TiO₂ based PSCs with PCE over 20% is achieved by isolating devices from oxygen and humidity. This achievement attributes to systematic understanding of the critical role of oxygen in the degradation of PSCs. PSCs exhibit fast degradation under controlled oxygen atmosphere and illumination, which is accompanied by iodine migration into the hole transport material (HTM). A diffusion barrier at the HTM/perovskite interface or encapsulation on top of the devices improves the stability against oxygen under light soaking. Notably, a mp‐TiO₂ based PSC with a solid encapsulation retains 20% efficiency after 1000 h of 1 sun (AM1.5G including UV) illumination in ambient air.

Surface‐clean and highly crystalline SnO₂ ETL is fabricated by a simple hydrothermal treatment at temperatures as low as 100 °C. The perovskite solar cells based on this hydrothermally treated SnO₂ ETL exhibit a champion PCE of 20.3% on a rigid ITO/Glass substrate, and a champion PCE of 18.1% and certified PCE of 17.3% on a flexible ITO/PEN substrate.

Abstract

Perovskite solar cells (PSCs) are one of the most promising solar energy conversion technologies owing to their rapidly developing power conversion efficiency (PCE). Low‐temperature solution processing of the perovskite layer enables the fabrication of flexible devices. However, their application has been greatly hindered due to the lack of strategies to fabricate high‐quality electron transport layers (ETLs) at the low temperatures (≈100 °C) that most flexible plastic substrates can withstand, leading to poor performances for flexible PSCs. In this work, through combining the spin‐coating process with a hydrothermal treatment method, ligand‐free and highly crystalline SnO₂ ETLs are successfully fabricated at low temperature. The flexible PSCs based on this SnO₂ ETL exhibit an excellent PCE of 18.1% (certified 17.3%). The flexible PSCs maintained 85% of the initial PCE after 1000 bending cycles and over 90% of the initial PCE after being stored in ambient air for 30 days without encapsulation. The investigation reveals that hydrothermal treatment not only promotes the complete removal of organic surfactants coated onto the surface of the SnO₂ nanoparticles by hot water vapor but also enhances crystallization through the high vapor pressure of water, leading to the formation of high‐quality SnO₂ ETLs.

A thicker bulk heterojunction film is successfully fabricated leading to generation of more carriers, extendsion of depleted region width, prolonged carrier lifetime, and improved carrier extraction efficiency. The highest short current density of 19.5 mA cm⁻², power conversion efficiency of 6.51% and the widest depletion region (177 nm) are obtained based on aqueous‐processed hybrid solar cells.

Abstract

Environmental friendly aqueous‐processed solar cells have become one of the most promising candidates for the next‐generation photovoltaic devices. Researchers have made lots of progress in designing active materials with novel structures, manipulating the defects in active materials, optimizing device architecture, etc. However, it has long been a challenge to control the width of the depletion region and enhance carrier extraction ability. Fabrication of a thick bulk heterojunction (BHJ) film is an effective strategy to address these issues but difficult to realize. Herein, the thicker BHJ film of ZnO:CdTe is successfully fabricated and incorporated into CdTe‐poly(p‐phenylenevinylene) hybrid solar cells. As expected, this BHJ film enhances light absorption, extends the width of the depletion region, prolongs carrier lifetime, and promotes carrier extraction ability. Moreover, the electron transport layer of sol–gel ZnO with excellent transmittance and electrical conductivity boosts electron generation, transport, and injection, which further improves the device performance. As a result, the highest short current density (J _sc) of 19.5 mA cm⁻², power conversion efficiency of 6.51%, and the widest depletion region (177 nm) are obtained in aqueous‐processed hybrid solar cells.

Publication date: 18 September 2019

Source: Joule, Volume 3, Issue 9

Author(s): Axel F. Palmstrom, Giles E. Eperon, Tomas Leijtens, Rohit Prasanna, Severin N. Habisreutinger, William Nemeth, E. Ashley Gaulding, Sean P. Dunfield, Matthew Reese, Sanjini Nanayakkara, Taylor Moot, Jérémie Werner, Jun Liu, Bobby To, Steven T. Christensen, Michael D. McGehee, Maikel F.A.M. van Hest, Joseph M. Luther, Joseph J. Berry, David T. Moore

Context & Scale

Summary

Graphical Abstract

Propane‐1,3‐diammonium cations are first adopted to construct cesium–formamidinium (Cs–FA) perovskite solar cells (PSCs) with an efficiency of 18.1% and much enhanced device stability, and the opposing effects induced by the diammonium cation are resolved.

Incorporating diammonium cations, which electrostatically connect the adjacent inorganic slabs ([PbI₆]⁴⁻), into 3D perovskite is recently proposed to develop high‐performance perovskite solar cells (PSCs). However, due to limited studies, the effects of these organic cations on the perovskite structural and optoelectronic properties are yet to be understood. Herein, a diammonium cation, propane‐1,3‐diammonium (PDA), is first proposed to modulate the cesium–formamidinium (Cs–FA)‐mixed cation perovskite. By increasing the PDA content, the efficiency of the Cs_0.15FA_{0.85 − x} PDA _x PbI₃ PSC first increases and then drastically decreases. The highest power conversion efficiency (PCE) of 18.10% obtained by Cs_0.15FA_0.83PDA_0.02PbI₃ is superior to that of the Cs_0.15FA_0.85PbI₃ (16.82%). Through systematic investigations, it is revealed that the PDA content–dependent efficiency is attributed to a competition between the enhanced defect passivation and emerged excitonic effect with an increased PDA content. Moreover, the encapsulated Cs_0.15FA_0.83PDA_0.02PbI₃ device exhibits almost 1.5 times increased stability than the Cs_0.15FA_0.85PbI₃ counterpart, with 83% of its initial efficiency retained after 500 h exposure, under continuous light soaking at 60 °C in ambient air. This study provides a practical strategy to enhance the device stability without sacrificing the efficiency and deepens our understanding on effects of diammonium cation incorporated in 3D perovskite.

10% Pb reduction in CsPb_0.9Zn_0.1I₂Br boosts the efficiency of the solar cell device. Zn²⁺ results in high quality crystalline and energy state modulation, greatly reducing the trap states and promoting the charge transport in the device. This work highlights that Zn is an effective and stable Pb reducer that compares well to the chemical unstable Sn, in efficient CsPbX₃ based PSCs.

Abstract

Fabrication of efficient Pb reduced inorganic CsPbI₂Br perovskite solar cells (PSC) are an important part of environment‐friendly perovskite technology. In this work, 10% Pb reduction in CsPb_0.9Zn_0.1I₂Br promotes the efficiency of PSCs to 13.6% (AM1.5, 1sun), much higher than the 11.8% of the pure CsPbI₂Br solar cell. Zn²⁺ has stronger interaction with the anions to manipulate crystal growth, resulting in size‐enlarged crystallite with enhanced growth orientation. Moreover, the grain boundaries (GBs) are passivated by the Cs‐Zn‐I/Br compound. The high quality CsPb_0.9Zn_0.1I₂Br greatly diminishes the GB trap states and facilitates the charge transport. Furthermore, the Zn4s‐I5p states slightly reduce the energy bandgap, accounting for the wider solar spectrum absorption. Both the crystalline morphology and energy state change benefit the device performance. This work highlights a nontoxic and stable Pb reduction method to achieve efficient inorganic PSCs.

The long‐term photostability under AM1.5G simulated 1 sun illumination including UV is demonstrated with the perovskite solar cell exceeding power conversion efficiency of 20%. This achievement stems from understanding the role of oxygen on the degradation under illumination. Oxygen induces iodine migration from the perovskite to a hole transport layer, which interrupts the charge transport through the interface.

Abstract

Perovskite solar cells (PSCs) with mesoporous TiO₂ (mp‐TiO₂) as the electron transport material attain power conversion efficiencies (PCEs) above 22%; however, their poor long‐term stability is a critical issue that must be resolved for commercialization. Herein, it is demonstrated that the long‐term operational stability of mp‐TiO₂ based PSCs with PCE over 20% is achieved by isolating devices from oxygen and humidity. This achievement attributes to systematic understanding of the critical role of oxygen in the degradation of PSCs. PSCs exhibit fast degradation under controlled oxygen atmosphere and illumination, which is accompanied by iodine migration into the hole transport material (HTM). A diffusion barrier at the HTM/perovskite interface or encapsulation on top of the devices improves the stability against oxygen under light soaking. Notably, a mp‐TiO₂ based PSC with a solid encapsulation retains 20% efficiency after 1000 h of 1 sun (AM1.5G including UV) illumination in ambient air.

Publication date: Available online 24 April 2019

Source: Nano Energy

Author(s): Qian Xie, Xunfan Liao, Lie Chen, Ming Zhang, Ke Gao, Bin Huang, Haitao Xu, Feng Liu, Alex K.-Y. Jen, Yiwang Chen

Graphical abstract

In this work, we successfully achieved a record fill factor (FF) of near 80% by using random copolymerization strategy to precisely control the morphology of active layer for polymer solar cells (PSCs).

Publication date: Available online 24 April 2019

Source: Nano Energy

Author(s): Yanliang Liu, Pesi Mwitumwa Hangoma, Vellaiappillai Tamilavan, Insoo Shin, In-Wook Hwang, Yun Kyung Jung, Bo Ram Lee, Jung Hyun Jeong, Sung Heum Park, Kwangho Kim

Graphical abstract

Efficient dual-functional light-emitting perovskite solar cells (LEPeSCs) have been demonstrated by using a new soft-covered annealing method. The LEPeSCs exhibits high performance in both solar cell (SC) and light emitting diode (LED) modes, with power conversion efficiency of 14.02% in SC mode and bright red-light emission of 1710 cd/cm2 at 4 V in LED mode.

Herein, the open‐circuit voltage losses and bias‐dependent photo‐ and electroluminescence of high‐performance 2D/3D perovskite solar cells, which exhibit outstanding optoelectronic properties, are investigated. These are state‐of‐the‐art photovoltaic devices. Results suggest that by reducing nonradiative recombination processes in the absorber, the power conversion efficiency of the studied photovoltaic devices can be improved.

Herein, the optoelectronic properties of interface‐engineered perovskite 2D|3D‐heterojunction structure solar cells are reported. The reciprocity theorem is applied to determine the maximum open‐circuit voltage (V _oc) the device can deliver under solar illumination. A V _oc of 1.295 V is found, analyzing the measured external quantum efficiency and assuming only radiative recombination. For comparison, the experimental open‐circuit voltage found for the studied 2D|3D heterojunctions is 1.15 V. The contribution of nonradiative recombination is explored by measuring the electroluminescence quantum yield. A quantum yield of 0.4% is found at current densities equivalent to 1 sun illumination. This translates into a V _oc loss of ≈140 mV, which is in very good agreement with the experimental findings. In addition, the fundamental correlation between luminescence intensity and the chemical potential predicted by the generalized Planck law is confirmed for the photoluminescence measured at different light intensities when the device is operated under open‐circuit conditions and for the electroluminescence when operated under a forward bias. The investigations in this study suggest that further efficiency improvements can be achieved by reducing the nonradiative recombination in the studied solar cell. At the same time, a high‐performance near IR light emitting diode can be realized.

Nature Communications, Published online: 14 May 2019; doi:10.1038/s41467-019-10098-z

Nature Energy, Published online: 13 May 2019; doi:10.1038/s41560-019-0393-3

Nature Energy, Published online: 13 May 2019; doi:10.1038/s41560-019-0389-z