Comparative Investigation of Fullerene PC71BM and Non-fullerene ITIC-Th Acceptors Blended With P3HT or PBDB-T Donor Polymers for PV Applications

Abstract

Fundamentally, organic solar cells (OSCs) with a bulk-heterojunction active layer are made of at least two electronically dissimilar molecules, in which photoabsorption in one (donor) generates Frenkel excitons. The formation of free charge carriers emerge after exciton dissociation at the donor:acceptor interface. In the past decade, most of the progress in enhanced device performance has been steered by the rapid development of novel donor and acceptor materials and on device engineering. Among these donor materials, regioregular poly(3-hexylthiophene) (P3HT) produced better performance despite the mismatch of its absorption coefficient with the solar emission spectrum. Comparatively the donor PBDB-T exhibits an outstanding absorption coefficient with a deeper-lying highest occupied molecular orbital (HOMO) level. Previously most of the efficient acceptors were based on fullerene molecules characterized by limited photoabsorption and stability. In contrast, the recently developed non-fullerene OSCs have a tunable absorption spectrum and exhibit improved stability. In this work, we explore the fundamental sources of the differences in the device performance for different blend compositions made of fullerene derivative (PC71BM) and non-fullerene (ITIC-Th) when paired with the polymer donors P3HT and PBDB-T. The characteristic changes of the optical properties of these blends and their roles in device performance are also investigated. We also studied charge generation where PBDB-T:PC71BM showed the highest maximum exciton generation rate (Gmax) of 3.22 × 1028 s–1 while P3HT: ITIC-Th gave the lowest (0.96 × 1028 s–1). Also noted, PC71BM based counterparts gave better charge transfer capabilities as seen from the lower PL quenching and higher charge carrier dissociation plus collection probability P(E,T) derived from a plot of Jph/Jsat ratio under short-circuit conditions against the effective voltages.

Scaling-Up of Solution-Processable Tungsten Trioxide (WO3) Nanoparticles as a Hole Transport Layer in Inverted Organic Photovoltaics

“…The absorption spectra in each case are consistent with the device performance in terms of JV curves and IPCE measurements, which are higher in the WO 3 -slot-die and spray-coated samples compared to the WO 3 -spin-coated samples. Furthermore, each device has a strong absorption in the range of 500-700 nm, which is consistent with the complementary absorbance spectra between PBDB-T:ITIC [60,61], indicating that ITIC molecules exhibit strong and wide-ranging absorption properties, spanning from the visible spectrum to the near infrared, with their peak absorption occurring at 700 nm.…”

Doping with Niobium Nanoparticles as an Approach to Increase the Power Conversion Efficiency of P3HT:PCBM Polymer Solar Cells

“…The band found at 821 cm −1 corroborates the existence of aromatic C-H outside of simple vibrations and suggests that the structure of P3HT is composed of P3HTchains [ 36 ]. The peak at 1107 cm −1 is ascribed to the asymmetries of the C-O stretching bands [ 37 ]. The carbon-to-carbon single bond (C-C) is represented by the band at 1270 cm −1 [ 38 ].…”

Charge carrier dynamics and photovoltaic properties of near-infrared absorbing squaraine incorporated solution-processed additive-free PTB7:PCBM based ternary solar cells

“…The saturation photocurrent, J sat is determined from figure 4(a) and the maximum generation rate, G max is calculated from J sat = qG max L, where, q is the elementary charge and L is the thickness of the active layer [23]. G max is a measure of the maximum number of photons that can be absorbed by the active layer [24]. It can be observed that there is an enhancement in the J sat and G max values with increase of SQ content in the OSCs, suggesting an enhancement in light absorption.…”

“…The excitons generated by the absorption of the photons may not be fully dissociated into free carriers in the active layer. The exciton dissociation probability, P(E, T), provides a measure of how many photogenerated excitons would be dissociated into free charge carriers [24]. The exciton dissociation probability rate is determined to be only 81.5% for the binary device under short-circuit conditions, while it improves to about 94.9% when 25 wt.% SQ is introduced into the ternary OSCs, indicative of effective dissociation of excitons at the donor/acceptor interface and accounting for the improved J SC .…”