New small organic molecules based on thieno[2,3-b]indole for efficient bulk heterojunction organic solar cells: a computational study

ABSTRACT

This study aims to evaluate the characteristics of novel organic D-π-A-π-D class small-molecules by using carefully the density functional theory, and time-dependent density functional theory calculations. Thedesigned sequence of (D-A) BHJ-1a to BHJ-4a in organic Bulk Heterojunction (BHJ) solar cells has been comprehensively analysed. Thiéno[2,3-b]indole (TI) has been used as donor, and Diketopyrrolopyrrole (DPP) as acceptor for all compounds. In order to improve the electronic, photovoltaic, and opticalproperties, we have substituted thiophene unit with furan, thieno[2,3-b]thiophene, thiazole and thiazolothiazole as π-bridge moieties. Thus, the result shows that the wise choice of the π-bridge units plays a significant role in improving E_gap, producing a high bathochromic shift, and increasing V_OC as well as a theoretical power conversion efficiency (PCE) over 7%. Interestingly, BHJ-4a with suitable π-bridge presents the optimal electronic properties with low band gap (1.870?eV) and high V_OC (1.534?eV). Furthermore, we have modelled a Bulk heterojunction organic photovoltaic cells based on donor-PCBM complex in order to achieve the optimum E_gap and V_OC. Consequently, the obtained results provide a new way to design BHJ small molecule donors with higher power conversion efficiency.     

Distributed feedback grating fabricated from hybrid polymer precursor gel by employing short‐pulse laser interference for photopumped polymer laser applications

The application of hybrid polymer precursor gel for distributed feedback (DFB) grating laser fabricated by short‐pulse laser interference has been investigated. The precursor gel was prepared by sol–gel process from siloxane‐modified methacrylate monomer. The molecular structure characterization results show the formation of inorganic networks within the precursor gel, which further undergoes the formation of organic–inorganic polymer network by photopolymerization. The laser interference was performed by using the frequency‐tripled output of nanosecond Nd–YAG laser. The fabricated DFB gratings exhibit photopumped lasing actions with high consistency between the grating periodicity (between 380 and 1030 nm) and the lasing wavelength, which appears at the wavelength of the second‐order Bragg reflection. The atomic force microcopy measurements clearly show the formation of surface relief (corrugated) structure in those gratings. The mechanism of surface relief formation is attributed to a fast photo‐induced swelling process, which is unique property belonging to this kind of hybrid polymer precursor gel. Copyright © 2011 John Wiley & Sons, Ltd.