Avoiding Photoinduced Shunts in Organic Solar Cells by the Use of Tin Oxide (SnO_x) as Electron Extraction Material Instead of ZnO

Abstract

low fi ll-factors (FFs) and overall low power conversion efficiency are found. This phenomenon is frequently referred to as "light-soaking" issue. [ 31,32 ] Development of charge extraction materials that do not rely on UV activation has been identifi ed to be of paramount importance to achieve highly effi cient and long-term stable devices. [ 33,34 ] In this sense, doped metaloxide EELs, e.g., Al:ZnO, [ 31,35,36 ] have been shown to mitigate the need for UV activation. While there are several reports of OSCs incorporating ZnO-based EELs in organic solar cells, which show a promising "shelf-life," [ 37 ] photoinduced shunts have been found to occur in the devices upon illumination "in actual operation." [38][39][40] Analogous to the case of the light activation discussed above, these photoinduced shunts are associated with the illumination by UV light (i.e., hν > E g ). As a result, a signifi cantly lowered shunt resistance along with a substantial decay of the FF and V oc is typically found to occur within minutes of illumination. The origin of this photoinduced shunt has been related to the UV-induced desorption of chemisorbed oxygen at the ZnO surface. [ 38 ] Approaches to modify and thereby to stabilize the ZnO surface range from the use of passivating mole cules [ 41 ] to the evaporation of thin aluminum layers onto the ZnO EEL. [ 39 ] Here, we will show that the photoinduced shunting behavior is a general phenomenon in OSCs comprising "neat or electrically doped" ZnO-based electron extraction layers, i.e., Al:ZnO (AZO) or Ga:ZnO (GZO), and it is found regardless if the EEL is prepared from nanoparticle dispersions or by vacuumbased techniques ( Figure 1 ). The photoinduced shunting of ZnO-based OSCs occurs for devices operated in air or under inert atmosphere, and it can therefore not be avoided by using a proper encapsulation. Moreover, we will show that while the photoinduced shunting is reversible in air, it is irreversible under the exclusion of oxygen. Opposed to ZnO-based EELs, we will demonstrate that the photoinduced shunting and the con-

UV-Induced Oxygen Removal for Photostable, High-Efficiency PTB7-Th:PC71BM Photovoltaic Cells

“…Such features indicate that the chemisorbed O 2 -defects on ZnO surface were significantly reduced by UVN treatment which led to the enhancement in electron concentration on the ZnO conduction band. However, one should note that UV exposures larger than 20 min increased the carrier concentration in the ZnO ETL to a level where carrier selectivity was lost and the cell electrical properties degraded 35 . This led to the reduction in FF and V oc seen in Figure 2E and to an increase in the series resistance seen in Table S1.…”

Solution‐Processed Tin Oxide‐PEDOT:PSS Interconnecting Layers for Efficient Inverted and Conventional Tandem Polymer Solar Cells

“…Solution‐processed tin oxide nanoparticles have emerged as an ETL in the field of perovskite solar cells . Also sol–gel tin oxide has been used for organic photovoltaic devices . Recently, Becker et al presented a tandem polymer solar cell with a molybdenum oxide/tin oxide ICL, where these layers were deposited by thermal evaporation and atomic layer deposition, respectively.…”

Probing electronic structure of stoichiometric and defective SnO2

“…Tin dioxide (SnO 2 ) is a prominent n-type semiconductor with widespread technological applications, such as gas sensing [1][2][3][4][5], catalysis [6,7], field effect transistors [8,9], organic solar cells [10,11], lithium ion batteries [12][13][14] and supercapacitors [15,16]. Knowledge of its electronic properties is key to understanding and predicting the efficacy of the materials used in these applications.…”