Overcoming the “Light‐Soaking” Issue in Inverted Organic Solar Cells by the Use of Al:ZnO Electron Extraction Layers

Abstract

A common phenomenon of organic solar cells (OSCs) incorporating metal‐oxide electron extraction layers is the requirement to expose the devices to UV light in order to improve device characteristics – known as the so‐called “light‐soaking” issue. This behaviour appears to be of general validity for various metal‐oxide layers, various organic donor/acceptor systems, and regardless if single junction devices or multi stacked cells are considered. The requirement of UV exposure of OSCs may impose severe problems if substrates with limited UV transmission, UV blocking filters or UV to VIS down‐conversion concepts are applied. In this paper, we will demonstrate that this issue can be overcome by the use of Al doped ZnO (AZO) as electron extraction interlayer. In contrast to devices based on TiOx and ZnO, the AZO devices show well‐behaved solar cell characteristics with a high fill factor (FF) and power conversion efficiency (PCE) even without the UV spectral components of the AM1.5 solar spectrum. As opposed to previous claims, our results indicate that the origin of s‐shaped characteristics of the OSCs is the metal‐oxide/organic interface. The electronic structures of the TiOx/fullerene and AZO/fullerene interfaces are studied by photoelectron spectroscopy, revealing an electron extraction barrier for the TiOx/fullerene case and facilitated electron extraction for AZO/fullerene. These results are of general relevance for organic solar cells based on various donor acceptor active systems.

Improved Performance and Reliability of p‐i‐n Perovskite Solar Cells via Doped Metal Oxides

“…It was also observed that UV light does not have any infl uence on PCBM/AZO/Al-based devices, an effect which is usually related to n-type metal oxide electron transporting layers in both organic and perovskite-based solar cells. [ 40 ] All the average and champion photovoltaic parameters of the two p-i-n solar cells under comparison are summarized in Table S1 (Supporting Information). The EQE shape is different in the region of 550-760 nm in the case of PCBM/AZO/Al cells.…”

Surface passivation effect by fluorine plasma treatment on ZnO for efficiency and lifetime improvement of inverted polymer solar cells

“…Through doping with group-II or group-III elements, an increase in the electrical conductivity of ZnO and, consequently, in the photovoltaic performance of PSCs with an inverted structure has been observed. [48][49][50][51][52] Besides the metal and also nitrogen doping which has also been reported to tune the properties of the zinc oxide surface, 53 our group and others recently introduced the beneficial surface modification of ZnO by using a hydrogen (H) plasma treatment for efficient inverted PSCs. 54,55 Plasma surface treatment is a process that alters the surface energy of many materials so as to improve the bonding characteristics.…”

Air-processed organic tandem solar cells on glass: toward competitive operating lifetimes

“…As such, future studies should primarily foster materials development of new absorbers with enhanced photo and structural stability as well as alternative electron transport layers that are not subject to the requirement of photodoping. [51][52][53][54] Moreover, fully solution processed tandem OPVs on exible plastics with state-of-the-art encapsulation need to be demonstrated for certifying market readiness.…”