Understanding the correlation between energy-state mismatching and open-circuit voltage loss in bulk heterojunction solar cells Hyun‐Seock Yang, Danbi Kim, Chang‐Mok Oh, Vellaiappillai Tamilavan, Pesi M. Hangoma, Hojun Yi, Bo R. Lee, Insoo Shin, In‐Wook Hwang, Sung Heum Park Carbon Energy, 2024 Photoinduced intermolecular charge transfer (PICT) determines the voltage loss in bulk heterojunction (BHJ) organic photovoltaics (OPVs), and this voltage loss can be minimized by inducing efficient PICT, which requires energy‐state matching between the donor and acceptor at the BHJ interfaces. Thus, both geometrically and energetically accessible delocalized state matching at the hot energy level is crucial for achieving efficient PICT. In this study, an effective method for quantifying the hot state matching of OPVs was developed. The degree of energy‐state matching between the electron donor and acceptor at BHJ interfaces was quantified using a mismatching factor (MF) calculated from the modified optical density of the BHJ. Furthermore, the correlation between the open‐circuit voltage (Voc) of the OPV device and energy‐state matching at the BHJ interface was investigated using the calculated MF. The OPVs with small absolute MF values exhibited high Voc values. This result clearly indicates that the energy‐state matching between the donor and acceptor is crucial for achieving a high Voc in OPVs. Because the MF indicates the degree of energy‐state matching, which is a critical factor for suppressing energy loss, it can be used to estimate the Voc loss in OPVs.
Enhanced photovoltaic performance for quinoxaline-based polymeric donor via backbone engineering for non-fullerene organic solar cells Rajalingam Agneeswari, Yoomi Ahn, Vellaiappillai Tamilavan, Danbi Kim, Insoo Shin, Hojun Yi, Chnan‐gi Shin, Sung Heum Park, Youngeup Jin Bulletin of the Korean Chemical Society, 2022 Herein, we demonstrate a facile technique for transforming a low‐energy‐converting quinoxaline‐based polymer into an efficient polymeric donor for non‐fullerene acceptor‐based organic solar cells (NFA‐OSCs). Alternating copolymers, namely P(BDTSi‐DTfQ), incorporating electron‐rich 4,8‐bis(triisopropylsilylethynyl)‐benzo[1,2‐b:4,5‐′]dithiophene (BDTSi) and electron‐deficient 2,3‐didodecyl‐6‐fluoro‐5,8‐di(thiophen‐2‐yl)quinoxaline (DTfQ) units were synthesized. The properties of P(BDTSi‐DTfQ) were thoroughly studied and briefly compared to those of the reported polymers, namely P(BDTSi‐DTffQ), made up of BDTSi and 2,3‐didodecyl‐6,7‐difluoro‐5,8‐di(thiophen‐2‐yl)quinoxaline (DTffQ) units. Polymer P(BDTSi‐DTfQ) exhibited a lower bandgap (Eg) and higher highest occupied and lowest unoccupied energy levels (HOMO and LUMO) than P(BDTSi‐DTffQ). The estimated Eg and HOMO/LUMO for P(BDTSi‐DTfQ) were 1.90 eV and −5.46 eV/−3.56 eV, respectively, and for P(BDTSi‐DTffQ) the same were 1.94 eV and −5.58 eV/−3.64 eV, respectively. Interestingly, the NFA‐OSCs made from P(BDTSi‐DTfQ) as the donor and NFA, namely ITIC, as the acceptor, gave a power conversion efficiency (PCE) of 3.68%, which is much higher than the PCE obtained (⁓0.75%) for the OSCs prepared by using the P(BDTSi‐DTffQ):ITIC blend. Noticeably, the energy levels of P(BDTSi‐DTfQ) were found to be favorable for efficient charge separation when it was blended with ITIC. This blend not only allowed a better charge separation at the donor/acceptor interfaces but also significantly lowered bimolecular recombination. The overall effect was to provide a higher PCE. However, P(BDTSi‐DTffQ) showed mismatched energy levels with ITIC resulting in a higher bimolecular recombination and lower PCE.
RECENT SCHOLAR PUBLICATIONS
Understanding the correlation between energy‐state mismatching and open‐circuit voltage loss in bulk heterojunction solar cells HS Yang, D Kim, CM Oh, V Tamilavan, PM Hangoma, H Yi, BR Lee, I Shin, ... Carbon Energy 6 (5), e433 , 2024 2024 Citations: 6
Enhanced photovoltaic performance for quinoxaline‐based polymeric donor via backbone engineering for non‐fullerene organic solar cells R Agneeswari, Y Ahn, V Tamilavan, D Kim, I Shin, H Yi, C Shin, SH Park, ... Bulletin of the Korean Chemical Society 43 (11), 1262-1270 , 2022 2022 Citations: 6
MOST CITED SCHOLAR PUBLICATIONS
Understanding the correlation between energy‐state mismatching and open‐circuit voltage loss in bulk heterojunction solar cells HS Yang, D Kim, CM Oh, V Tamilavan, PM Hangoma, H Yi, BR Lee, I Shin, ... Carbon Energy 6 (5), e433 , 2024 2024 Citations: 6
Enhanced photovoltaic performance for quinoxaline‐based polymeric donor via backbone engineering for non‐fullerene organic solar cells R Agneeswari, Y Ahn, V Tamilavan, D Kim, I Shin, H Yi, C Shin, SH Park, ... Bulletin of the Korean Chemical Society 43 (11), 1262-1270 , 2022 2022 Citations: 6
