Addition of a small fraction of high boiling point solvent into the host of donor/acceptor blend is one the best approach to control the morphology in order to enhance the power conversion efficiency of organic bulk heterojunction (BHJ) solar cell devices. Herein, we focus on the effect of two thiol-based additives (1,6-hexanedithiol (HDT) and 1,5-pentanedithiol (PDT)) on the charge dynamics of P3HT:PCBM blend system, studied by transient absorption spectroscopy (TAS) and correlated with the solar cell device performance. TAS reveals a more efficient charge generation and polaron formation in the systems with additives as compared to those without (NA systems), at the onset which persists up to few microseconds. The recombination dynamics also exhibits the reduced recombination losses on adding these additives in this system; however, there is marginal change of recombination dynamics in PDT added system with the control. These charge dynamics were validated using the analytical model proposed in our previous work and also correlated with improved device performance (ηNA = 0.9%, ηHDT = 2.7%, ηPDT = 1.6%).
Solution-processed hybrid organic-inorganic perovskite solar cells, a newcomer to the photovoltaic arena, have taken the field by
storm with their extraordinary power conversion efficiencies exceeding 17%. In this paper, the photophysics and the latest findings on the carrier dynamics and charge transfer mechanisms in this new class of photovoltaic material will be examined and distilled. Some open photophysics questions will also be discussed.
The blending of metallic nanoparticles into the active layer of organic solar cells in a bid to enhance their light
absorption and device performance has led to controversial reports of both efficiency enhancement and degradation.
Herein, through comprehensive transient absorption spectroscopy, we present clear evidence of traps being responsible
for performance degradation of poly (3-hexylthiophene): [6,6]-phenyl-C 61-butyric acid methyl ester organic
photovoltaic devices incorporated with oleylamine-capped silver nanoparticles. Although the presence of the metallic
nanoparticles leads to more excitons being generated in the active layer, higher losses suffered by the polaron population
through trap-assisted recombination strongly limits the device performance. Device modeling based on a single mid-gap
trap state introduced by the AgNPs can well reproduce the current-voltage curves of the plasmonic organic solar cells –
in agreement with the transient absorption findings. These new insights into the photophysics and charge dynamics of
plasmonic organic solar cells would help resolve the existing controversy and provide clear guidelines for device design
Proton beam writing is a new direct write lithographic technique that utilizes a high energy (MeV) submicron focused proton beam to machine or modify a material, usually a polymer. Structures made using p-beam writing have very smooth side walls, high aspect ratio, and a scale that can be easily matched to existing optical fiber
technology (0.1 to 1000 μm). In this paper we demonstrate the use of proton beam writing for prototyping micro-optical components such as microlens arrays and gratings in positive and negative resist. The structures that are fabricated can be used for both rapid prototyping and for large scale replication with nanoimprint
Proton beam writing is a new direct-write micromachining technique capable of producing 3-dimensional (3-D), high aspect ratio micro-structures with straight and smooth sidewalls. It uses a focused sub-micron beam of 2.0 MeV protons to direct-write on a suitable polymer, such as the photoresists: poly-methylmethacrylate (PMMA) and SU-8, a negative tone photoresist from MicroChem. In this paper, we report on the application of proton beam writing to fabricate low-loss passive polymer waveguide structures such as symmetric y-branching waveguides in SU-8. SU-8 channel waveguides are fabricated by first direct-writing the pattern using a proton beam and subsequently chemically developing the latent image formed. A UV-cured resin, Norland Optical Adhesive 88 (NOA-88) is used as the cladding layer. Being a direct-write technique, proton beam writing offers us great flexibility to fabricate waveguides of arbitrary patterns and this is an asset that can be applied to the rapid prototyping of optical circuits. With all its unique characteristics, proton beam writing is an excellent technique for waveguide fabrication.