Variations of cell performance in ITO-free organic solar cells with increasing cell areas

Abstract

This study examined the effects of a cell area on the cell performances in ITO-free organic solar cells (OSCs) based on poly(3-hexylthiophene) (P3HT) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 (PCBM). Highly conductive poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films with two different sheet resistances (Rsh) were used as polymeric transparent anodes for cost-effective ITO-free OSCs. Changes in the power conversion efficiency (PCE), the fill factor (FF), the short-circuit current (Jsc), and the open-circuit voltage (Voc) that resulted from changing the cell area or sheet resistance of transparent electrodes were systematically investigated. With increasing cell area from 4.5 to 49.5 mm2, the device performance of ITO-free OSCs was continuously decreased mainly due to the decrease in the FF and the series resistance (Rs). In addition, the performance of OSCs was critically dependent on Rsh of the PEDOT:PSS electrode. Upon reducing Rsh of the polymer anode from ∼200 to ∼90 Ω/□, the FF and PCE showed better values at an identical large cell area and exhibited a relieved cell performance degradation with increasing cell area, suggesting that the sheet resistance of transparent electrodes is a dominant factor to limit cell efficiencies in practical large-area solar cells.