| 초록 |
Recently, solution-processed polymer solar cells and perovskite solar cells have emerged as a promising class of photovoltaic devices because of record-breaking progress in the device performance with maintaining their many advantages, including flexibility and a low cost fabrication. The power conversion efficiency (PCE) has been steeply improved during the past several years and currently exceeded 16% for polymer solar cells and 24% for perovskite solar cells. However, there is still room for further improvements in PCE when taking into account the Shockley–Queisser (SQ) limit (30–33%) for single junction photovoltaic devices with a bandgap of absorber (1.0–1.6 eV). To achieve such an upper limit of PCE, it is of key importance to suppress voltage loss (photon energy loss, Eloss = Eg − qVOC) in both devices because it is much larger than the loss (0.25–0.30 eV) that is only driven by an inevitable radiative recombination. Thus, one of the issues emerging is how much Eloss can be reduced for both solar cells in this community. In this talk, I will address the origin of Eloss in both polymer solar cells and perovskite solar cells.1,2 By measuring the temperature dependence of VOC, we found that there are temperature-independent and -dependent voltage losses in polymer solar cells while there is only a temperature-dependent voltage loss in perovskite solar cells. This discrepancy is ascribed to different charge generation and recombination mechanisms between them. In particular, for polymer solar cells, I will focus on a comparison of Eloss for the devices based on a fullerene derivative PCBM and a non-fullerene acceptor ITIC with almost the same LUMO level. The impact of charge recombination mechanism on Eloss, and thus on photovoltaic performance, will be addressed on the basis of cyclic voltammetry and temperature dependence of VOC measurements. Finally, I will try to highlight a primary loss mechanism in Eloss for these two classes of solar cells and how we can suppress this. (1) H. D. Kim et al., ACS Appl. Mater. Interfaces, 9, 19988 (2017). (2) H. D. Kim et al., Chem. Lett., 46, 253 (2017). |
