The energy costs associated with separating tightly bound excitons (photoinduced electron-hole pairs) and extracting free charges from highly disordered low-mobility networks represent fundamental losses for many low-cost photovoltaic technologies. We report a low-cost, solution-processable solar cell, based on a highly crystalline perovskite absorber with intense visible to near-infrared absorptivity, that has a power conversion efficiency of 10.9% in a single-junction device under simulated full sunlight. This "meso-superstructured solar cell" exhibits exceptionally few fundamental energy losses; it can generate open-circuit photovoltages of more than 1.1 volts, despite the relatively narrow absorber band gap of 1.55 electron volts. The functionality arises from the use of mesoporous alumina as an inert scaffold that structures the absorber and forces electrons to reside in and be transported through the perovskite.

https://science.sciencemag.org/content/sci/early/2012/10/03/science.1228604.full.pdf

Efficient Hybrid Solar Cells Based on Meso-Superstructured Organometal Halide Perovskites

Graphene’s success has shown that it is possible to create stable, single and few-atom-thick layers of van der Waals materials, and also that these materials can exhibit fascinating and technologically useful properties. Here we review the state-of-the-art of 2D materials beyond graphene. Initially, we will outline the different chemical classes of 2D materials and discuss the various strategies to prepare single-layer, few-layer, and multilayer assembly materials in solution, on substrates, and on the wafer scale. Additionally, we present an experimental guide for identifying and characterizing single-layer-thick materials, as well as outlining emerging techniques that yield both local and global information. We describe the differences that occur in the electronic structure between the bulk and the single layer and discuss various methods of tuning their electronic properties by manipulating the surface. Finally, we highlight the properties and advantages of single-, few-, and many-layer 2D materials in...

/pdf/progress-challenges-and-opportunities-in-two-dimensional-1sweg4hljr.pdf

Progress, Challenges, and Opportunities in Two-Dimensional Materials Beyond Graphene

Graphene-Like Two-Dimensional Materials

Circularly polarized light has been used to confine charge carriers in single-layer molybdenum disulphide entirely to a single energy-band valley, representing full valley polarization.

Control of valley polarization in monolayer MoS2 by optical helicity

Ever since its discovery, the Berry phase has permeated through all branches of physics. Over the last three decades, it was gradually realized that the Berry phase of the electronic wave function can have a profound effect on material properties and is responsible for a spectrum of phenomena, such as ferroelectricity, orbital magnetism, various (quantum/anomalous/spin) Hall effects, and quantum charge pumping. This progress is summarized in a pedagogical manner in this review. We start with a brief summary of necessary background, followed by a detailed discussion of the Berry phase effect in a variety of solid state applications. A common thread of the review is the semiclassical formulation of electron dynamics, which is a versatile tool in the study of electron dynamics in the presence of electromagnetic fields and more general perturbations. Finally, we demonstrate a re-quantization method that converts a semiclassical theory to an effective quantum theory. It is clear that the Berry phase should be added as a basic ingredient to our understanding of basic material properties.

/pdf/berry-phase-effects-on-electronic-properties-53dkbbi2er.pdf

Berry phase effects on electronic properties

Device Characteristics of CZTSSe Thin‐Film Solar Cells with 12.6% Efficiency

The path towards a high-performance solution-processed kesterite solar cell ☆

Using vacuum process, we fabricated Cu2ZnSnS4 solar cells with 8.4% efficiency, a number independently certified by an external, accredited laboratory. This is the highest efficiency reported for pure sulfide Cu2ZnSnS4 prepared by any method. Consistent with literature, the optimal composition is Cu-poor and Zn-rich despite the precipitation of secondary phases (e.g., ZnS). Despite a very thin absorber thickness (~600 nm), a reasonably good short-circuit current was obtained. Time-resolved photoluminescence measurements suggest a minority carrier-diffusion length on the order of several hundreds of nanometers and relatively good collection of photo-carriers across the entire absorber thickness. Copyright © 2011 John Wiley & Sons, Ltd.

Thin film solar cell with 8.4% power conversion efficiency using an earth‐abundant Cu2ZnSnS4 absorber

Beyond 11% Efficiency: Characteristics of State‐of‐the‐Art Cu2ZnSn(S,Se)4 Solar Cells

A power conversion efficiency record of 10.1% was achieved for kesterite absorbers, using a Cu2ZnSn(Se,S)4 thin-film solar cell made by hydrazine-based solution processing. Key device characteristics were compiled, including light/dark J–V, quantum efficiency, temperature dependence of Voc and series resistance, photoluminescence, and capacitance spectroscopy, providing important insight into how the devices compare with high-performance Cu(In,Ga)Se2. The record kesterite device was shown to be primarily limited by interface recombination, minority carrier lifetime, and series resistance. The new level of device performance points to the significant promise of the kesterites as an emerging and commercially interesting thin-film technology. Copyright © 2011 John Wiley & Sons, Ltd.

Oki Gunawan

Papers

Device Characteristics of CZTSSe Thin‐Film Solar Cells with 12.6% Efficiency

The path towards a high-performance solution-processed kesterite solar cell ☆

Thin film solar cell with 8.4% power conversion efficiency using an earth‐abundant Cu2ZnSnS4 absorber

Beyond 11% Efficiency: Characteristics of State‐of‐the‐Art Cu2ZnSn(S,Se)4 Solar Cells

Device characteristics of a 10.1% hydrazine-processed Cu2ZnSn(Se,S)4 solar cell