Electrical, photodiode, and DFT studies of newly synthesized π-conjugated BODIPY dye-based Au/BOD-Dim/n-Si device

Abstract

A π-conjugated 4,4-difluoro-4- bora-3a,4a-diaza-s-indacene (BODIPY) dimer (BOD-Dim) compound has been synthesized and characterized. The optimized molecular structure, the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) simulations, and static isotropic polarizability of the isolated compound were computed via the Gaussian program. The simulated static dielectric constant value was calculated. The effect of the BOD-Dim interlayer on the diode characteristics of the Au/n-Si diode was investigated. The electrical and photovoltaic parameters of the Au/BOD-Dim/n-Si/In diode such as ideality factor (n), barrier height (Φ_B), open-circuit voltage (V_oc), short-circuit current (J_sc), photosensitivity (S), and photoresponsivity (R) have been investigated by current-voltage measurements at dark and under various illumination intensities. The possible current conduction mechanism has been examined through the forward bias ln(I_F)-ln(V_F) and ln(I_R)-V_R^1/2 characteristics. All obtained results confirmed that Au/BOD-Dim/n-Si/In diode exhibits a photovoltaic behavior and presents great potential as a photosensor for optoelectronic device applications.

Introduction

The interest on studies related to the development of solution processable small π-conjugated semiconducting organic molecules has been increased recently in view of their technological applications [[1], [2], [3]]. Due to their π-conjugated molecular structure which allows charge carriers to be transmitted via a hopping process, organic semiconductor have exciting electrical and optoelectronic properties. Also, in their low cost and easy preparation techniques and their chemical stability and tunable optical properties, organic semiconductors have been employed in electronic, optoelectronic, and photonic devices [2,[4], [5], [6], [7], [8], [9], [10], [11], [12], [13]]. Organic semiconductors are thought to be alternatives to inorganic semiconductors, as they offer various properties such as mechanical flexibility, solubility in various organic solvents, easy processing for device manufacturing, chemical and thermal stability, and relatively low cost. Considering the abovementioned properties, it is not unexpected that the usage areas of organic semiconductors will expand further in the near future.

The interest on studies related to Schottky contacts obtained by contacting metals with semiconductors has been arisen in last decades due to their possible usage in several applications. It is known that the interface state densities at the metal semiconductor (MS) interface have a significant influence on the electrical parameters of a Schottky contact. Besides, the performance and stability of devices are sensitive to interfacial properties of metal-semiconductor contacts. There are many studies in the literature that reveal the advantages of using hybrid organic-inorganic heterojunction in a single structure for diode parameters. For instance, in the past few decades, metal-organic interlayer-semiconductor type Schottky barrier diodes which obtained by forming an organic semiconductor layer on an inorganic semiconductor have been made to improve the electrical characteristics of the device [10,11,[14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24]].

Organic semiconductors can be found either as small molecules, oligomers, or polymers. Organic dyes, in particular, are of widespread interest in the use of organic semiconductors due to their good solubility in different solvents which make them suitable for easy device fabrication via spin coating [14,16,[18], [19], [20],22,[25], [26], [27]]. Among many semiconducting organic dyes in the last decades, derivatives of BODIPY, one of the most popular fluorescent dye, have emerged as an important class of materials that have high hole mobility due to their large π-conjugated structure [[28], [29], [30]]. Yet other advantages of BODIPY dyes are their high extinction coefficients, easy functionalization technique as well as good chemical and photochemical stabilities. In this respect, BODIPY dyes seem to be good candidates for organic semiconductors which can be useful for optoelectronic and photovoltaic devices. For these reasons, the BODIPY core which is a remarkable semiconducting structure has often been used for various applications such as dye-sensitized solar cells, photovoltaics, and organic electronics [[29], [30], [31], [32]]. Among these studies, few studies on the effect of using π-conjugated BODIPY compounds as an interlayer on the structural and optical properties of Au/n-Si thin film were found in the literature [29,[33], [34], [35]]. In this context, the synthesis of π-extended BODIPY derivatives with high semiconductivity level is still desired to show their potential in Schottky barrier diodes (SBDs).

The main aim of this study is to investigate the effect of π-extended BODIPY interlayer on the diode characteristics of the Au/n-Si diode. For this purpose, a π-extended BODIPY derivative (BOD-Dim) was designed and synthesized. Its chemical structure was confirmed by ¹H and ¹³C spectroscopy. Then, Au/n-Si/BOD-Dim/In diode was fabricated by spin-coating technique, and its illumination dependence of electrical and photoelectrical properties were determined by using I–V measurements.