Electrical and Optical Properties of ZnO Processed by Atomic Layer Deposition in Inverted Polymer Solar Cells

Abstract

We report on the photovoltaic properties of inverted polymer solar cells where the transparent electron-collecting electrode is formed by a ZnO-modified indium−tin oxide (ITO) electrode. The ZnO layers were deposited by atomic layer deposition (ALD) with varying thicknesses from 0.1 to 100 nm. The work function, surface roughness, and morphology of ITO/ZnO were found to be independent of the ZnO thickness. However, the device performance was found to be strongly dependent on a critical ZnO thickness, around 10 nm. Below the critical thickness the device performance was degraded because of the appearance of a “kink” in the current−voltage characteristics. The kink features became less pronounced after ultraviolet (UV) exposure. This was attributed to oxygen desorption, leading to an increased conductivity of the ZnO layer. At and above this critical thickness, the device performance significantly improved and no longer depended strongly on the thickness of the ZnO layer, in agreement with optical simulations. Instead, these optical simulations showed that the thickness of the active layer plays a more important role than the thickness of the ZnO layer in optimizing the photovoltaic properties of inverted solar cells. Inverted polymer solar cells with an increased thickness of the active layer showed a power conversion efficiency (PCE) of 3.06% estimated for AM1.5G, a 100 mW cm−2 illumination.

Ambient Layer‐by‐Layer ZnO Assembly for Highly Efficient Polymer Bulk Heterojunction Solar Cells

“…Though ZnO ETL for solar cells generally can be prepared by various methods, such as atomic layer deposition, [ 29 ] electro deposition, [ 25 ] spin-coating, [ 30 ] spray-coating, [ 31 ] and the sol-gel technique, [ 26,32 ] it is well known that low-temperature solutionprocessed amorphous ZnO layers usually yield poor device performance with a reported maximum PCE of ≈3.2%. [ 31 ] This indicates that low-temperature processing of ZnO may introduce substantial microstructural and/or morphological imperfections into the donor-acceptor network, which could be detrimental to many applications.…”

Effects of ultraviolet soaking on surface electronic structures of solution processed ZnO nanoparticle films in polymer solar cells

“…The conductivity of ZnO films is thought to be negatively affected by chemisorbed oxygen and this can in turn negatively impact the efficiency of the PCS. 23 The surface conductivity of ZnO films is decreased as chemisorbed oxygen molecules capture electrons from the ZnO conduction band creating a near-surface depletion region with a then comparatively high resistivity. [24][25][26] Oxygen molecules can also diffuse into the ZnO film where they chemisorb and create a potential barrier between and a depletion region along either side of the grain boundary, thus reducing the bulk conductivity of the film.…”

Design and synthesis of indole-substituted fullerene derivatives with different side groups for organic photovoltaic devices

“…As we all know, the size of the crystal domains could be calculated according to the Scherrer equation [42]:…”

“…Inverted photovoltaic devices, which have the advantage of stability in air, have recently attracted high interest [42]. To investigate the relationship between the chemical structures of the fullerene derivatives and photovoltaic properties, we used OIHC60P, OIMC60P, OIBC60P, OIB2FC60P, and OIB5FC60P as acceptors to fabricate inverted photovoltaic devices (ITO/ZnO/P3HT: fullerene derivatives/MoO 3 /Ag).…”