Ming Zhu

This paper presents the development and implementation of a high-sensitivity external quantum efficiency (sEQE) measurement system designed to characterize optoelectronic devices, particularly solar cells and photodetectors. Our setup enables precise measurement of the conversion efficiency of photons into free charge carriers, providing crucial insights into device performance and underlying physical mechanisms. The measurement setup is based on a white-light source coupled to a monochromator for wavelength selection, with the diffracted beam focused onto either a calibrated photodiode or the device under test. Mea- surements can be performed at room temperature using a custom sample holder or across a range of temperatures using a cryostat. Signal detection is achieved through Lock-In amplifi- cation, enabling high sensitivity in noisy environments. The incorporation of spectral filters and multiple photodiodes with extended calibration ranges enables a dynamic range span- ning six orders of magnitude, allowing detection of sub-bandgap signals. Beyond describing component modularity and hardware specifications, we provide open-source Python-based control and analysis software to control the sEQE setup and analyze the resulting data. This comprehensive documentation of both hardware and software components contributes to an ongoing effort to increase transparency, standardization, and reproducibility in experimental research and aims to ease access to an important characterization technique for solar cells and photodetectors.

The record power conversion efficiency of solution-processed organic solar cells (OSCs) has almost doubled since non-fullerene acceptors (NFAs) replaced fullerene derivatives as the best-performing acceptor molecules. The successful transition from C60 to NFAs is still pending for vacuum-thermal evaporated (VTE) OSCs, not least because most NFAs are too large to be evaporated without breaking. Due to VTE’s relevance in terms of industrial manufacturing, discovering high-performing VTE NFAs is a major opportunity for OSCs. Here, we fabricate evaporated OSCs based on the NFA BTIC-H known from solution processing. This A–D–A molecule has an unfused bithiophene core, 1,1-dicyanomethylene-3-indanone end groups, and hexyl side chains, making it small enough to be evaporated well. We pair BTIC-H with four commonly used evaporated donors—DCV5T-Me(3,3), DTDCPB, HB194, and SubNc—in planar heterojunctions. We observe appreciable photocurrents and a voltage loss of ∼0.8 V, matching that of corresponding C60 devices. Donor:BTIC-H bulk heterojunctions likely face charge collection issues due to unfavorable microstructure. Our work demonstrates one of few NFA based evaporated OSCs with encouraging performance results and gives one potential starting point for molecule design of further NFAs suitable for VTE.