We demonstrate single layer graphene/n-Si Schottky junction solar cells that under AM1.5 illumination exhibit a power conversion efficiency (PCE) of 8.6%. This performance, achieved by doping the graphene with bis(trifluoromethanesulfonyl)amide, exceeds the native (undoped) device performance by a factor of 4.5 and is the highest PCE reported for graphene-based solar cells to date. Current–voltage, capacitance–voltage, and external quantum efficiency measurements show the enhancement to be due to the doping-induced shift in the graphene chemical potential that increases the graphene carrier density (decreasing the cell series resistance) and increases the cell’s built-in potential (increasing the open circuit voltage) both of which improve the solar cell fill factor.

http://absimage.aps.org/image/MAR13/MWS_MAR13-2012-000669.pdf

High Efficiency Graphene Solar Cells by Chemical Doping

Hybrid perovskites are promising semiconductors for optoelectronic applications. However, they suffer from morphological disorder that limits their optoelectronic properties and, ultimately, device performance. Recently, perovskite single crystals have been shown to overcome this problem and exhibit impressive improvements: low trap density, low intrinsic carrier concentration, high mobility, and long diffusion length that outperform perovskite-based thin films. These characteristics make the material ideal for realizing photodetection that is simultaneously fast and sensitive; unfortunately, these macroscopic single crystals cannot be grown on a planar substrate, curtailing their potential for optoelectronic integration. Here we produce large-area planar-integrated films made up of large perovskite single crystals. These crystalline films exhibit mobility and diffusion length comparable with those of single crystals. Using this technique, we produced a high-performance light detector showing high gain (above 10(4) electrons per photon) and high gain-bandwidth product (above 10(8) Hz) relative to other perovskite-based optical sensors.

/pdf/planar-integrated-single-crystalline-perovskite-43a58ibpwg.pdf

Planar-integrated single-crystalline perovskite photodetectors

In the past decade graphene has been one of the most studied material for several unique and excellent properties. Due to its two dimensional nature, physical and chemical properties and ease of manipulation, graphene offers the possibility of integration with the exiting semiconductor technology for next-generation electronic and sensing devices. In this context, the understanding of the graphene/semiconductor interface is of great importance since it can constitute a versatile standalone device as well as the building-block of more advanced electronic systems. Since graphene was brought to the attention of the scientific community in 2004, the device research has been focused on the more complex graphene transistors, while the graphene/semiconductor junction, despite its importance, has started to be the subject of systematic investigation only recently. As a result, a thorough understanding of the physics and the potentialities of this device is still missing. The studies of the past few years have demonstrated that graphene can form junctions with 3D or 2D semiconducting materials which have rectifying characteristics and behave as excellent Schottky diodes. The main novelty of these devices is the tunable Schottky barrier height, a feature which makes the graphene/semiconductor junction a great platform for the study of interface transport mechanisms as well as for applications in photo-detection, high-speed communications, solar cells, chemical and biological sensing, etc. In this paper, we review the state-of-the art of the research on graphene/semiconductor junctions, the attempts towards a modeling and the most promising applications.

Graphene Schottky diodes: an experimental review of the rectifying graphene/semiconductor heterojunction

This paper proposes and examines three different plots for the determination of the saturation current, the ideality factor, and the series resistance of Schottky diodes and solar cells from the measurement of a single current (I)/voltage(V) curve. All three plots utilize the small signal conductance and avoid the traditional Norde plot completely. A test reveals that the series resistance and the barrier height of a test diode can be determined with an accuracy of better than 1%. Finally it is shown that a numerical agreement between measured and fittedI/V curves is generally insufficient to prove the physical validity of current transport models.

Schottky barrier and pn-junction I/V plots — Small signal evaluation

Graphene Schottky diodes: An experimental review of the rectifying graphene/semiconductor heterojunction

It is shown that by using the forward current density‐voltage (J‐V) characteristics of a Schottky diode, a plot of d(V)/d(ln J) vs J and a plot of the function H(J) vs J, where H(J)≡V−n(kT/q)ln(J/A**T2), will each give a straight line. The ideality factor n, the barrier height φB, and the series resistance R of the Schottky diode can be determined with one single I‐V measurement. This procedure has been used successfully to study thermal annealing effects of W/GaAs Schottky contacts.

N. W. Cheung

Papers

Extraction of Schottky diode parameters from forward current-voltage characteristics