WSe₂ Photovoltaic Device Based on Intramolecular p–n Junction

Abstract

High quality p–n junctions based on 2D layered materials (2DLMs) are urgent to exploit, because of their unique properties such as flexibility, high absorption, and high tunability which may be utilized in next‐generation photovoltaic devices. Based on transfer technology, large amounts of vertical heterojunctions based on 2DLMs are investigated. However, the complicated fabrication process and the inevitable defects at the interfaces greatly limit their application prospects. Here, an in‐plane intramolecular WSe2 p–n junction is realized, in which the n‐type region and p‐type region are chemically doped by polyethyleneimine and electrically doped by the back‐gate, respectively. An ideal factor of 1.66 is achieved, proving the high quality of the p–n junction realized by this method. As a photovoltaic detector, the device possesses a responsivity of 80 mA W−1 (≈20% external quantum efficiency), a specific detectivity of over 1011 Jones and fast response features (200 µs rising time and 16 µs falling time) at zero bias, simultaneously. Moreover, a large open‐circuit voltage of 0.38 V and an external power conversion efficiency of ≈1.4% realized by the device also promises its potential in microcell applications.

Lateral 2D WSe2 p–n Homojunction Formed by Efficient Charge‐Carrier‐Type Modulation for High‐Performance Optoelectronics

“…According to the power law I ph = c × P κ (c is a proportionality constant and κ is an empirical value), [24] the experimental results are linearly fitted with the value κ = 0.966, which exhibits a better linear fitting than previous reports. [18,25] This linear relationship between the photocurrent and the photoflux clarifies the fact that the measured electrical signals are dominated by the photogenerated charge carriers of the WSe 2 channel rather than the thermionic or tunneling current. The photoresponsivity of the device upon illumination is defined as R = ph I PS in units of A W −1 , where I ph is the photocurrent, P the incident light power density, and S the active area.…”

“…Figure b plots the photocurrent ( I ph = I illumination − I dark ) of the photodetectors ( V ds = 0.5 V) at various laser power densities ( P ). According to the power law I ph = c × P κ ( c is a proportionality constant and κ is an empirical value), the experimental results are linearly fitted with the value κ = 0.966, which exhibits a better linear fitting than previous reports . This linear relationship between the photocurrent and the photoflux clarifies the fact that the measured electrical signals are dominated by the photogenerated charge carriers of the WSe 2 channel rather than the thermionic or tunneling current.…”

“…Note that although the bias voltage increases, the calculated value of detectivity stays at a high value about 10 11 Jones, which represents the excellent performance of the device to detect weak signals with low noise. The summarized photonic parameters (R, EQE, D*, and I light /I dark ) are much higher than the reported 2D lateral and vertical TMDs p-n junction-based photodetectors, [18,19,27,[30][31][32][33][34] as shown in Table S1 (Supporting Information).…”

“…Due to the merits of high light absorption and unique band structure which enables facile bipolar manipulation of carrier type, 2D WSe 2 has great potential in realizing p–n junctions for next‐generation photovoltaic devices . To achieve the transformation from p‐type to n‐type carrier in low‐dimensional TMDs, surface charge transfer is an efficient route to modulate the electrical properties of TMDs by inducing a shift of Fermi level effectively.…”

Multifunctional black phosphorus/MoS2 van der Waals heterojunction

“…The current-rectifying characteristic can be modulated by V g , as shown in Figure S3. When V g = 10 V, a rectification ratio of 182 is obtained at V d = −1/+1 V. To specify the ideal factor (n) of the p-n diode, we fitted the experimental output results at different V g in the volt-ampere characteristic function [Equation (S1)] [29]. It is found that the experimental data fit well with the function, and a minimum value of 1.59 is achieved when V g = −30 V, as shown in Figure 2F and Figure S4.…”