On the Interplay between CT and Singlet Exciton Emission in Organic Solar Cells with Small Driving Force and Its Impact on Voltage Loss
On the Interplay between CT and Singlet Exciton Emission in Organic Solar Cells with Small Driving Force and Its Impact on Voltage Loss
复制标题
DOI：
10.1002/aenm.202200641
复制
发表时间：
2022-06-28
影响因子：
27.8
通讯作者：
Neher, Dieter
中科院分区：
文献类型：
--
作者：
Fritsch, Tobias;Kurpiers, Jona;Neher, Dieter
自由载流子、电荷转移(CT)态和单重态激子(S-1)之间的相互作用决定了有机太阳能电池的复合途径和由此产生的开路电压(V-OC)。通过将具有不同共混比例的聚集态低禁带聚合物PCBM和ICBA结合在一起，CT态的能量(E-CT)变化了130meV，而聚合物的S-1能量(Es1[{E{Rm{S}]不受影响)。结果表明，当ECT值接近Es1时，聚合物激子主导了共混物的辐射性能，而V-OC仍受CT态的非辐射衰变的限制。结果表明，有机太阳电池光谱中激子强度的增加通常会降低非辐射电压损失，因为它降低了辐射的V-OC极限(V-OC，V-rad)，而不是因为它的发射性更强。分析进一步表明，CT态与S一号之间的电子耦合不会提高V-OC，反而会降低V-OC、V-rad。预计只有在非常低的CT态吸收和相当高的CT辐射效率的情况下，太阳能电池才能受益于单重态激子的辐射特性。
The interplay between free charge carriers, charge transfer (CT) states and singlet excitons (S-1) determines the recombination pathway and the resulting open circuit voltage (V-OC) of organic solar cells. By combining a well-aggregated low bandgap polymer with different blend ratios of the fullerenes PCBM and ICBA, the energy of the CT state (E-CT) is varied by 130 meV while leaving the S-1 energy of the polymer (ES1\[{E_{{{\rm{S}}_1}}}\]) unaffected. It is found that the polymer exciton dominates the radiative properties of the blend when ECT\[{E_{{\rm{CT}}}}\] approaches ES1\[{E_{{{\rm{S}}_1}}}\], while the V-OC remains limited by the non-radiative decay of the CT state. It is concluded that an increasing strength of the exciton in the optical spectra of organic solar cells will generally decrease the non-radiative voltage loss because it lowers the radiative V-OC limit (V-OC,V-rad), but not because it is more emissive. The analysis further suggests that electronic coupling between the CT state and the S-1 will not improve the V-OC, but rather reduce the V-OC,V-rad. It is anticipated that only at very low CT state absorption combined with a fairly high CT radiative efficiency the solar cell benefit from the radiative properties of the singlet excitons.