Dynamic Characterization of Hybrid Solar Cells Based on Polymer and Aligned ZnO Nanorods by Intensity Modulated Photocurrent Spectroscopy

Abstract

For characterization of polymer-based solar cells with vertically aligned ZnO nanorod arrays (ZnO-NAs) by intensity modulated photocurrent spectroscopy (IMPS), a dynamic IMPS model is developed, where the structure-related charge generation and transport dynamics are considered. The model describes the IMPS responses affected by the phase shift φ n (ω) due to the exciton diffusion property (ω 0 ) and the structurerelated device ideality factor N, the electron diffusion coefficient D e , the exciton dissociation rate S, and the device structure (e.g., nanorod length d and interspacing l). The main expectations of the model are confirmed by the experimental data of the polymer/ZnO-NA cells with d ) 180-650 nm, offering mechanistic information on the structure-related charge generation, charge transport, and device performance. The presence of the φ n (ω) makes IMPS response not spiral into the origin and the phase angle in its Bode plot not tend to 90°; the d-dependent direct diffusion (DD) and diffusion-reflection (DF) transport processes are normally involved in the travel of injected electrons to the collection electrode; the incident photon-to-current conversion efficiency (IPCE) and the transit time (τ D ) for DD transport under the influence of DF process reach their peak values at d ≈ 500 nm, and the φ n (ω) effect on electron transport is affected by ω 0 , D e , and S. Satisfactory fittings of measured IMPS responses to the model further reveal that the d dependence of the IPCE or the photocurrent actually originates from the S value governed by d-dependent exciton generation and dissociation; when changing d, a larger number of electrons for DD transport causes a smaller N or a more remarkable φ n (ω) effect; a longer τ D is accompanied by a larger RC effect of the ZnO electrode. Those results clearly suggest that a highly efficient polymer/ZnO-NA device requires d ≈ 500 nm and l ) 5-10 nm, along with a high interfacial exciton dissociation efficiency.

Preferentially oriented large antimony trisulfide single-crystalline cuboids grown on polycrystalline titania film for solar cells

“…It should be noted that the efficiency of the present solar cell is not high enough yet. We envision that, for a better device performance, it is necessary to reduce the surface roughness of the Sb 2 S 3 layer, which may cause serious shorting risk 44 and charge recombination 11,45 to reduce V oc and FF values, to improve the charge collection efficiency in the device.…”

“…IMPS spectra were measured on a controlled intensity modulated photo spectroscopy (CIMPS, Zahner Co., Germany; Thales 4.15 Software) in ambient conditions. During IMPS measurements 45 , the solar cells was illuminated with a modulated illumination (I) formed by a dc component of a steady-state background light I 0 and an ac component of a small sinusoidal perturbation I ac = I 0 δe iωt , that is, I = I 0 (1 + δe iωt ), where the background light intensity I 0 of 10 mW/cm 2 was provided by a blue light-emitting diode (BLL01, λ max = 470 nm, spectral half-width = 25 nm, Zahner Co.) driven by a frequency response analyzer and the perturbation was applied in the frequency range from 1 Hz to 100 kHz with a modulation depth of δ = 0.10. During the J-V and IMPS measurements, the illumination area of each device was limited by a mask with an aperture (2 × 2 mm 2 ), which actually defined the effective area for getting photovoltaic parameters of the device.…”

Solution-processed solar cells based on inorganic bulk heterojunctions with evident hole contribution to photocurrent generation

“…28 During the J-V and dynamic measurements, the illumination was limited to the overlapped area (1 Â 4 mm 2 ) between FTO and Au by a photomask attached to each device. Steady-state J-V characteristics were measured under AM 1.5 illumination with an intensity of 100 mW cm À2 from a 94023A Oriel Sol3A solar simulator (Newport Stratford, Inc.), and the light intensity from a 450 W xenon lamp was calibrated with a standard crystalline silicon solar cell; the J-V curves were collected with an Oriel s I-V test station (PVIV-1A, Keithley 2400 Source Meter, Labview 2009 SP1 GUI Software, Newport).…”

“…This derivation should correlate with the simplification that our model (eqn (3)) does not consider the influence of charge carrier concentration on electron transport and the detailed kinetics of the transport process; hence, our model should only tentatively describe the IMPS shape and does not provide real dynamic characteristics in practical devices. 28 3.2.3. 7b), which is not related to the turning point for the process change from electron transport to hole relaxation ( Fig.…”

“…S9, ESI †) is located only in the IV quadrant, indicating no photogenerated hole contribution to the photocurrent according to our theoretical model. S9, ESI †) indicated that the Sb 2 S 3 /TiO 2 -BHJ solar cell with T c = 300 1C predominantly involves the excitonic mechanism, 28,47 with exciton diffusion in the Sb 2 S 3 layer toward the Sb 2 S 3 /TiO 2 interface for dissociation and no evident hole contribution to photocurrent generation due to the very serious hole trapping by the defect states in the nanostructured Sb 2 S 3 layer, which is different from the nonexcitonic mechanism 76 in the Sb 2 S 3 /TiO 2 -BHJ solar cells with T c = 350 and 400 1C (Fig. 7b), suggesting that the photovoltaic mechanism in the solar cell with T c = 300 1C is different from those with T c = 350 and 400 1C.…”