Probing the Low Fill Factor of NiO p-Type Dye-Sensitized Solar Cells

Abstract

p-Type dye-sensitized solar cells (p-DSCs) have attracted increasing attention recently, but they suffer from low fill factors (FFs) and unsatisfactory efficiencies. A full comprehension of the hole transport and recombination processes in the NiO p-DSC is of paramount importance for both the fundamental study and the practical device optimization. In this article, NiO p-DSCs were systematically probed under various bias and illumination conditions using electrochemical impedance spectroscopy (EIS), intensity modulated photocurrent spectroscopy (IMPS), and intensity modulated photovoltage spectroscopy (IMVS). Under the constant 1 sun illumination, the recombination resistance (R rec ) of the cell deviates from an exponential relationship with the potential and saturates at ∼130 Ω cm 2 under the short circuit condition, which is ascribed to the overwhelming recombination with the reduced dye anions. Such a small R rec results in the small dc resistance, which decreases the "flatness" of the J−V curve. The quantitative analysis demonstrates that the FF value is largely attenuated by the recombination of holes in NiO with the reduced dyes. Our analysis also shows that if this recombination can be eliminated, then an FF value of 0.6 can be reached, which agrees with the theoretical calculation with a V oc of 160 mV.

Optimizing CuO p-type dye-sensitized solar cells by using a comprehensive electrochemical impedance spectroscopic study

“…Finally, the effective diffusion lengths L eff -eqn (5) -the effective diffusion coefficients of the charge carriers D effeqn (6) -and the charge collection efficiencies η cc can be calculated -eqn (7): 16,26,27 …”

Combining Electron‐Accepting Phthalocyanines and Nanorod‐like CuO Electrodes for p‐Type Dye‐Sensitized Solar Cells

“…A similar trend has recently been reported for NiO-based DSSCs. [28] Overall, ZnPc2 devices give rise to lower RCTs throughout the entire voltage range relative to ZnPc1 devices, indicating better charge injection and charge transport in the former. At Voc conditions, the recombination across the electrode/electrolyte interface dominates due to the lack of external currents.…”

“…Applying different voltages to change between short-circuit current density and open-circuit voltage conditions assists in probing the aforementioned processes in p-type DSSCs. [27,28] As an illustration, the Nyquist plots under Voc and Jsc conditions are shown in Figure S6. Here, two semicircles, which relate to the resistance across the platinum/electrolyte interface in the high frequency region and the dye/electrode/electrolyte interface in the low frequency region are discernable.…”

“…Additional device properties, namely the chemical capacitance (Cµ), the charge collection efficiency (ηcc), the effective diffusion length (Leff), and the effective diffusion coefficient (Deff) have been determined for all devices and are summarized in Figure S8. [28,30] Briefly, Cµ directly correlates with the density of injected holes at the electrode. A higher rate of charge injection increases the hole density, affording higher Voc and Cµ.…”

Antiferromagnetic structures and electronic energy levels at reconstructed NiO(111) surfaces: ADFT+Ustudy

“…Mesoporous NiO interfaced with an organic dye has been studied [28,29] and shown to achieve the photoconversion efficiency of 1.3% in context of p-type DSSC in recent years [28]. However, this device exhibits low powerconversion efficiencies in p-DSSCs devices, which has been interpreted as a consequence of several reasons, including small open circuit voltage (V OC ), low hole mobility, poor chromophore surface loading, and high charge carrier recombination rates [30,31]. By synthesizing the nanoplatelets with the (111) surface exposed, Flynn and co-workers have recently investigated the p-DSSC performance and its dependence on various annealing conditions for the synthesis [32].…”