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

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) C-61 (PCBM). Highly conductive poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT:PSS) films with two different sheet resistances (R-sh) 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 (J(sc)), and the open-circuit voltage (V-oc) 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 mm(2), the device performance of ITO-free OSCs was continuously decreased mainly due to the decrease in the FF and the series resistance (R-s). In addition, the performance of OSCs was critically dependent on Rsh of the PEDOT: PSS electrode. Upon reducing Rsh of the polymer anode from similar to 200 to similar to 90 Omega/square, 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.