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Light‐induced performance degradation in organic solar cells (OSCs) is a major impediment to their commercialization. As the photostability of OSCs strongly depends on the material's properties, the most effective solution for this concern is to develop a photostable material. However, the wide variety of causes of photo‐instability in a standard multilayered OSC structure complicates the evaluation of photostability of newly developed materials. To address this challenge, a top‐gate field‐effect transistor (FET) as a testbed for evaluating the photostability of OSC materials is proposed. This device test platform minimizes the internal and external origins of photo‐instability by employing a fluoropolymer gate dielectric. The photostability of an OSC material incorporated in this FET testbed can be evaluated by monitoring light‐induced mobility degradation. Two types of common donor polymers with similar chemical structures and crystallinity are employed as test materials, and their photostability is evaluated. The test results correspond to the photostability measurements conducted in the standard OSC structure, validating the proposed FET testbed. The proposed FET testbed enables rapid evaluation of the photostability of a newly developed OSC material, thereby providing timely feedback to material scientists. This boosts the development of photostable OSC materials.

Organic polymer semiconductor‐based polymer solar cells (PSCs) are drawing tremendous research interest for their superior electrical, structural, optical, mechanical, and chemical properties. During the last two decades, immense efforts have been made toward the development of PSCs. Generally, poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is used as hole transport layer (HTL) of PSCs to improve hole extraction efficiency, but highly acidic PEDOT:PSS reduces device lifetime by destroying indium tin oxide (ITO) electrodes and active layers. To avoid this, some have attempted to develop inverted structured PSCs with different electron transport layers (ETLs); however, the power conversion efficiency (PCE) of these devices is limited owing to low electron mobility of their ETLs. Therefore, an attempt is made to improve the PCE of an inverted‐structured PSC by using indium gallium zinc oxide (IGZO) with optimized amount of indium (In), gallium (Ga), and zinc (Zn). Inverted PSCs with ZnO or IGZO (having various molar ratios of In, Ga, and Zn) as ETL with the structure ITO/ETL/PTB7:PC71BM/MoO3/Al are constructed. The PCE of the inverted PSC can be increased from 6.22% to 8.72% by using IGZO with an optimized weight ratio of In, Ga, and Zn as an ETL.

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