Built-in potential shift and Schottky-barrier narrowing in organic solar cells with UV-sensitive electron transport layers

Abstract

The performance of organic solar cells incorporating solution-processed titanium suboxide (TiOx) as electron-collecting layers can be improved by UV illumination. We study the mechanism of this improvement using electrical measurements and electroabsorption spectroscopy. We propose a model in which UV illumination modifies the effective work function of the oxide layer through a significant increase in its free electron density. This leads to a dramatic improvement in device power conversion efficiency through several mechanisms - increasing the built-in potential by 0.3 V, increasing the conductivity of the TiOx layer and narrowing the interfacial Schottky barrier between the suboxide and the underlying transparent electrode. This work highlights the importance of considering Fermi-level equilibration when designing multi-layer transparent electrodes.

Interfacial Control Toward Efficient and Low‐Voltage Perovskite Light‐Emitting Diodes

“…The device shows characteristics similar to those of the NIR-emitting devices, such as subbandgap turn-on at 2.2 V (Figure 4 b) and bias-independent emission spectral shape ( Figure S9, Supporting Information). We note that for green LEDs, there are no previous results [ 23,24,39,40 ] COMMUNICATION showing a brightness of >10 000 cd m −2 at an operational voltage of below 3 V achieved by solution-processed polymer or quantum dot LEDs and even vacuum-deposited small-molecule LEDs. A maximum luminance of 20 000 cd m −2 was attained under a driving voltage of as low as 2.8 V. The high brightness achieved at the low voltage can be attributed to small energy losses from carrier injection and high mobility ambipolar carrier transport.…”

“…All layers, with the exception of the MoO x /Au electrode, were deposited from solutions. MoO x /Au bilayers [ 24 ] and ITO with PEImodifi ed ZnO [ 25 ] were selected as the top and bottom electrodes, respectively because of their ohmic carrier injection properties.Figure 2 a shows the EL spectra of the NIR device at various bias voltages. The wide bandgap ZnO nanocrystals were employed as electron-transporting and hole-blocking layers because of the combination of high electron mobility, excellent optical transparency, and a deep valence-band energy level.…”

“…A schematic of the fl at-band energy-level diagram is shown in Figure 1 b. MoO x /Au bilayers [ 24 ] and ITO with PEImodifi ed ZnO [ 25 ] were selected as the top and bottom electrodes, respectively because of their ohmic carrier injection properties. The TFB was used as a hole-transporting and electron-blocking interlayer due to its high hole mobility, low electron affi nity (≈2.1 eV), and high ionization potential (≈5.4 eV).…”

Origins and mechanisms of hysteresis in organometal halide perovskites

“…Several groups have made efforts on the construction of a band diagram, based on indirect evidences, such as transient photocurrent [80] and surface potential characterization [85]. Furthermore electroabsorption spectroscopy [97][98][99] has proven as a powerful approach to study the internal electrical field, enabling to directly characterize the field of device in working condition and observe any occurring interfacial barrier modulations [100]. Li et al [10]found that there is a shift of the built-in potential during the device scanning, as shown in Figure 15.…”

Influence of Electron Extracting Interface Layers in Organic Bulk‐Heterojunction Solar Cells

“…EA measurements have been also carried out on organic solar cells to estimate the internal field . The detailed EA experiment has been described elsewhere in literature . In short, an electric‐field modulation, i.e., a superposition of DC and AC voltages, is applied to the device and the relative change in intensity of the reflective probe light, Δ R , is monitored using a silicon detector connected with a lock‐in amplifier.…”