Charge Transfer in Ternary Solar Cells Employing Two Fullerene Derivatives: Where do Electrons Go?
Charge Transfer in Ternary Solar Cells Employing Two Fullerene Derivatives: Where do Electrons Go?
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DOI：
10.1002/ijch.202100064
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发表时间：
2021-10
影响因子：
3.2
通讯作者：
A. Sperlich;Michael Auth;V. Dyakonov
中科院分区：
文献类型：
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作者：
A. Sperlich;Michael Auth;V. Dyakonov
早期的报道表明，由供体聚合物（D）与富勒烯受体（A：A）的不同混合物混合制成的三元有机太阳能电池（OSC）表现非常相似。这一发现令人惊讶，因为相应的富勒烯LUMO能级略有不同，这可能导致电荷转移步骤的决定性差异。我们研究了三元OSC（D：A：A）的供体聚合物P3HT与不同的富勒烯衍生物的化学计量混合物，PC60BM：PC70BM和PC70BM：IC60BA，分别。使用定量电子顺磁共振（EPR），我们可以区分正和负极化子，定位在特定的分子。我们发现，在初始的电荷转移步骤后，电子重新分布在两个附近的受体在协议与他们的化学计量和他们的相对LUMO能量差。值得注意的是，与原始材料相比，富勒烯混合物中测得的Δ LUMO差异降低了一个数量级，即，低于1meV的PC60BM：PC70BM和（20 ± 5）meV的PC70BM：IC60BA。此外，我们发现这种降低的Δ LUMO解释了D：A：A有机太阳能电池开路电压的变化。我们将这些发现归因于杂交，导致有效的富勒烯LUMO。因此，多受体共混物确实是光电探测器和太阳能电池的可行选择，因为它们联合收割机最好的电子受体和光吸收性能。
Earlier reports demonstrated that ternary organic solar cells (OSC) made of donor polymers (D) blended with different mixtures of fullerene acceptors (A:A) performed very similarly. This finding is surprising, as the corresponding fullerene LUMO levels are slightly different, which might result in decisive differences in the charge transfer step. We investigate ternary OSC (D:A:A) made of the donor polymer P3HT with stoichiometric mixtures of different fullerene derivatives, PC60BM:PC70BM and PC70BM:IC60BA, respectively. Using quantitative electron paramagnetic resonance (EPR) we can distinguish between positive and negative polarons, localized on the specific molecules. We found that after the initial charge transfer step, the electrons are re-distributed over two nearby acceptors in agreement with their stoichiometry and their relative LUMO energy difference. Remarkably, the measured ∆LUMO differences in fullerene mixtures are reduced by an order of magnitude compared to that of the pristine materials, i.e., below 1 meV for PC60BM:PC70BM and (20 ± 5) meV for PC70BM:IC60BA. Furthermore, we found that this reduced ∆LUMO explains the shift in open circuit voltage for D:A:A organic solar cells. We attribute these findings to hybridization, leading to an effective fullerene LUMO. Consequently, multi-acceptor blends are indeed a viable option for photodetectors and solar cells, as they combine the best electron acceptor and light absorbing properties.