Elongated Lifetime and Enhanced Flux of Hot Electrons on a Perovskite Plasmonic Nanodiode.

A fundamental understanding of hot electron transport is critical for developing efficient hot-carrier-based solar cells. There have been significant efforts to enhance hot electron flux, and it has been found that a key factor affecting the hot electron flux is the lifetime of the hot electrons. Here, we report a combined study of hot electron flux and the lifetime of hot carriers using a perovskite-modified plasmonic nanodiode. We found that perovskite deposition on a plasmonic nanodiode can considerably improve hot electron generation induced by photon absorption. The perovskite plasmonic nanodiode consists of MAPbI3 layers covering a plasmonic-Au/TiO2 Schottky junction that is composed of randomly connected Au nanoislands deposited on a TiO2 layer. The measured incident photon-to-electron conversion efficiency and the short-circuit photocurrent show a significantly improved solar-to-electrical conversion performance of this nanodiode. Such an improvement is ascribed to the improved hot electron flux in MAPbI3 caused by effective light absorption from near-field enhancement of plasmonic Au and the efficient capture of hot electrons from Au nanoislands via the formation of a three-dimensional Schottky interface. The relation between the lifetime and flux of hot electrons was confirmed by femtosecond transient absorption spectroscopy that showed considerably longer hot electron lifetimes in MAPbI3 combined with the plasmonic Au structure. These findings can provide a fundamental understanding of hot electron generation and transport in perovskite, which can provide helpful guidance to designing efficient hot carrier photovoltaics.

Efficient and Reproducible CH3NH3PbI3 Perovskite Layer Prepared Using a Binary Solvent Containing a Cyclic Urea Additive.

An efficient CH3NH3PbI3 perovskite solar cell whose performance is reproducible and shows reduced dependence on the processing conditions is fabricated using the cyclic urea compound 1,3-dimethyl-2-imidazolidinone (DMI) as an additive to the precursor solution of CH3NH3PbI3. X-ray diffraction analysis reveals that DMI weakly coordinates with PbI2 and forms a CH3NH3PbI3 film (film-DMI) with no intermediate phase. The surface of annealed film-DMI (film-DMI-A) was smooth, with an average crystal size of 1 µm. Photoluminescence and transient photovoltage measurements show that film-DMI-A exhibits a longer carrier lifetime than a CH3NH3PbI3 film prepared using the strongly coordinating additive dimethyl sulfoxide (DMSO) (film-DMSO-A) because of the reduced number of defect sites in film-DMI-A. A solar cell based on film-DMI-A exhibits a higher power conversion efficiency (17.6%) than that of a cell based on film-DMSO-A (15.8%). Furthermore, the performance of the film-DMI-A solar cell is less sensitive to the ratio between PbI2 and DMI, and film-DMI can be fabricated under a high relative humidity of 55%.

Impact of Interfacial Layers in Perovskite Solar Cells.

Perovskite solar cells (PCSs) are composed of organic-inorganic lead halide perovskite as the light harvester. Since the first report on a long-term-durable, 9.7 % efficient, solid-state perovskite solar cell, organic-inorganic halide perovskites have received considerable attention because of their excellent optoelectronic properties. As a result, a power conversion efficiency (PCE) exceeding 22 % was certified. Controlling the grain size, grain boundary, morphology, and defects of the perovskite layer is important for achieving high efficiency. In addition, interfacial engineering is equally or more important to further improve the PCE through better charge collection and a reduction in charge recombination. In this Review, the type of interfacial layers and their impact on photovoltaic performance are investigated for both the normal and the inverted cell architectures. Four different interfaces of fluorine-doped tin oxide (FTO)/electron-transport layer (ETL), ETL/perovskite, perovskite/hole-transport layer (HTL), and HTL/metal are classified, and their roles are investigated. The effects of interfacial engineering with organic or inorganic materials on photovoltaic performance are described in detail. Grain-boundary engineering is also included because it is related to interfacial engineering and the grain boundary in the perovskite layer plays an important role in charge conduction, recombination, and chargecarrier life time.

High-Performance Long-Term-Stable Dopant-Free Perovskite Solar Cells and Additive-Free Organic Solar Cells by Employing Newly Designed Multirole π-Conjugated Polymers.

Perovskite solar cells (PSCs) and organic solar cells (OSCs) are promising renewable light-harvesting technologies with high performance, but the utilization of hazardous dopants and high boiling additives is harmful to all forms of life and the environment. Herein, new multirole π-conjugated polymers (P1-P3) are developed via a rational design approach through theoretical hindsight, further successfully subjecting them into dopant-free PSCs as hole-transporting materials and additive-free OSCs as photoactive donors, respectively. Especially, P3-based PSCs and OSCs not only show high power conversion efficiencies of 17.28% and 8.26%, but also display an excellent ambient stability up to 30 d (for PSCs only), owing to their inherent superior optoelectronic properties in their pristine form. Overall, the rational approach promises to support the development of environmentally and economically sustainable PSCs and OSCs.

Visible light absorption and photoelectrochemical activity of colorless molecular 1,3-bis(dicyanomethylidene)indane (BDMI) by surface complexation on TiO2.

Adsorption of the colorless 1,3-bis(dicyanomethylidene)indane (BDMI) onto a nanocrystalline TiO2 surface unusually turned the BDMI a deep blue color. Upon contact of the BDMI-adsorbed TiO2 (BDMI-TiO2) with an iodide-based redox electrolyte, a photocurrent density as high as 14.9 mA cm(-2) was generated with a photovoltage of 0.42 V, leading to a power conversion efficiency of 3.63%. This unprecedented photovoltaic performance was simultaneously investigated by spectroscopic studies of BDMI-TiO2 films and density functional theory (DFT)/time-dependent DFT (TD-DFT) computational approaches for [BDMI](-)[Ti(OH)3·H2O](+) (1) as a simple model compound to inspect the light to current conversion abilities. All these results established that the color change from colorless to deep blue and the highly efficient photocurrent generation through binding on the TiO2 surface originates from interfacial charge transfer transitions from anionic BDMI to TiO2.

High-efficiency perovskite solar cells based on the black polymorph of HC(NH2)2 PbI3.

Perovskite solar cells with power conversion efficiencies exceeding 16% at AM 1.5 G one sun illumination are developed using the black polymorph of formamidnium lead iodide, HC(NH2)2 PbI3 . Compared with CH3 NH3 PbI3 , HC(NH2 )2 PbI3 extends its absoprtion to 840 nm and shows no phase transition between 296 and 423 K. Moreover, a solar cell based on HC(NH2 )2 PbI3 exhibits photostability and little I-V hysteresis.