Po-Wei Liang

Additive Enhanced Crystallization of Solution‐Processed Perovskite for Highly Efficient Planar‐Heterojunction Solar Cells

P.-W. Liang, C.-Y. Liao, Dr. C.-C. Chueh, Dr. F. Zuo, S. T. Williams, Dr. X.-K. Xin, Prof. A. K.-Y. Jen Department of Materials Science and Engineering University of Washington Seattle , WA 98195 , USA E-mail: ajen@u.washington.edu Prof. A. K.-Y. Jen Department of Chemistry University of Washington Seattle , WA 98195 , USA C.-Y. Liao, Prof. J. J. Lin Institute of Polymer Science and Engineering National Taiwan University Taipei 106 , Taiwan

High-Performance and Environmentally Stable Planar Heterojunction Perovskite Solar Cells Based on a Solution-Processed Copper-Doped Nickel Oxide Hole-Transporting Layer

An effective approach to significantly increase the electrical conductivity of a NiOx hole-transporting layer (HTL) to achieve high-efficiency planar heterojunction perovskite solar cells is demonstrated. Perovskite solar cells based on using Cu-doped NiOx HTL show a remarkably improved power conversion efficiency up to 15.40% due to the improved electrical conductivity and enhanced perovskite film quality. General applicability of Cu-doped NiOx to larger bandgap perovskites is also demonstrated in this study.

Role of Chloride in the Morphological Evolution of Organo-Lead Halide Perovskite Thin Films

A comprehensive morphological study was used to elucidate chlorides role in CH(3)NH(3)PbI(3-x)Cl(x) film evolution on a conducting polymer, PEDOT:PSS. Complex ion equilibria and aggregation in solution, as well as the role they play in nucleation, are found to ultimately be responsible for the unique morphological diversity observed in perovskite films grown in the presence of the chloride ion. An intermediate phase that is generated upon deposition and initial annealing templates continued self-assembly in the case of CH(3)NH(3)PbI(3-x)Cl(x). In the absence of chloride, the film growth of CH(3)NH(3)PbI(3) is directed by substrate interfacial energy. By employing the through-plane TEM analysis, we gain detailed insight into the unique crystallographic textures, grain structures, and elemental distributions across the breadth of films grown from precursor solutions with different chemistries. The lattice coherence seen in morphologies generated under the influence of chloride provides a physical rational for the enhancement in carrier diffusion length and lifetime.

Suppressed Charge Recombination in Inverted Organic Photovoltaics via Enhanced Charge Extraction by Using a Conductive Fullerene Electron Transport Layer

Conductive fullerene electron-transporting layers (ETLs) are developed to facilitate the solution processing of highly efficient inverted OSCs with power conversion efficiency (PCE) reaching 9.6%. Its high conductivity also allows devices to be fabricated independently of the ETL thickness (up to ca. 50 nm). Transient photovoltage (TPV) measurements are used to shed light on how these conductive ETLs help suppress charge recombination in solar cells.

Binary‐Metal Perovskites Toward High‐Performance Planar‐Heterojunction Hybrid Solar Cells

A simple, low temperature solution process for Pb/Sn binary-metal perovskite planar-heterojunction solar cells is demonstrated. Sn inclusion substantially influences the band-gap, crystallization kinetics, and thin-film formation leading to a broadened light absorption and enhanced film coverage on ITO/PEDOT:PSS. As a result, the optimized device shows a PCE exceeding 10%, which is the best result for binary-metal perovskite solar cells so far.

Doping of Fullerenes via Anion‐Induced Electron Transfer and Its Implication for Surfactant Facilitated High Performance Polymer Solar Cells

Simple and solution-processible tetrabutyl-ammonium salts (TBAX) can dope fullerene and its derivatives to achieve conductive thin films (σ as high as 0.56 S/m). The electron transfer between the anions of TBAXs and n-type semiconductors induces doping without encountering any harsh activation. These provide valid support for the surfactant interfacial doping of fullerene in polymer solar cells for enhanced device performance.

The roles of alkyl halide additives in enhancing perovskite solar cell performance

Alkyl halide additives have been investigated to elucidate their effects in enhancing perovskite solar cell performance. We found that the additives can participate in the perovskite formation via dissociated halides, suggesting that molecular structure of alkyl halide additives plays multiple roles in modulating the dynamics of perovskite crystal growth.

Highly Efficient Perovskite–Perovskite Tandem Solar Cells Reaching 80% of the Theoretical Limit in Photovoltage

Organic-inorganic hybrid perovskite multijunction solar cells have immense potential to realize power conversion efficiencies (PCEs) beyond the Shockley-Queisser limit of single-junction solar cells; however, they are limited by large nonideal photovoltage loss (V oc,loss ) in small- and large-bandgap subcells. Here, an integrated approach is utilized to improve the V oc of subcells with optimized bandgaps and fabricate perovskite-perovskite tandem solar cells with small V oc,loss . A fullerene variant, Indene-C60 bis-adduct, is used to achieve optimized interfacial contact in a small-bandgap (≈1.2 eV) subcell, which facilitates higher quasi-Fermi level splitting, reduces nonradiative recombination, alleviates hysteresis instabilities, and improves V oc to 0.84 V. Compositional engineering of large-bandgap (≈1.8 eV) perovskite is employed to realize a subcell with a transparent top electrode and photostabilized V oc of 1.22 V. The resultant monolithic perovskite-perovskite tandem solar cell shows a high V oc of 1.98 V (approaching 80% of the theoretical limit) and a stabilized PCE of 18.5%. The significantly minimized nonideal V oc,loss is better than state-of-the-art silicon-perovskite tandem solar cells, which highlights the prospects of using perovskite-perovskite tandems for solar-energy generation. It also unlocks opportunities for solar water splitting using hybrid perovskites with solar-to-hydrogen efficiencies beyond 15%.

Modulation of hybrid organic–perovskite photovoltaic performance by controlling the excited dynamics of fullerenes

We present a synergistic approach to modulate organic–perovskite interfaces and their photovoltaic behaviors by tuning the properties of n-contact fullerenes layered atop of perovskite. Fullerenes with excited charge transfer are found to not only suppress fullerene photoluminescence, but also enhance molecular polarization and transport capabilities. This results in optimized perovskite–fullerene contact.

Design rules for the broad application of fast (<1 s) methylamine vapor based, hybrid perovskite post deposition treatments

While organo-metal halide perovskite photovoltaics have seen rapid development, growth of high quality material remains a challenge. Herein, we report a facile post deposition treatment utilizing coordination between methylamine (CH3NH2) vapor and CH3NH3PbI3 perovskite that rapidly improves film quality, enhancing power conversion efficiency (PCE) by ∼9%. We further comprehensively analyze the physical impact of this process with regard to the materials optoelectronic properties and its detailed microstructural changes. Connecting this with an analysis of the source of organo-metal halide perovskite reactivity toward the vapor as well as phase behavior as a function of CH3NH2 vapor pressure and time, we provide design rules for the broad, rational extension of this process to new systems and scales.