Structure–Property Correlation: A Comparison of Charge Carrier Kinetics and Recombination Dynamics in All-Polymer Solar Cells

Abstract

We report a comparison of charge carrier kinetics and recombination dynamics correlated with the device performances of PBDTTT-C and PBDTTT-CT in nonfullerene P­(NDI2OD-T2) solar cells. The nanoscale morphological characteristics are found to be remarkably different for these two polymers in all-polymer bulk heterojunction (BHJ) blends. Important insights into the carrier dynamics and crystalline packing features of these different donor materials are provided in detail. The higher device performance of the PBDTTT-CT:P­(NDI2OD-T2) device [2.78% compared to 1.56% for the PBDTTT-C:P­(NDI2OD-T2) cell] is shown to result from efficient charge generation and faster carrier separation, reducing nongeminate recombination during charge collection, which is attributed to the perfect intermixing between the donor and acceptor polymer networks.

Critical Role of Pendant Group Substitution on the Performance of Efficient All-Polymer Solar Cells

“…A common feature of high-efficiency APSCs is the use of donors with bulky pendant units such as thiophene or phenyl units in the polymer side chains. − A dramatic example of the efficacy of such bulky side groups is the comparison of solar cell efficiencies achieved using either PTB7 or PTB7-Th as donor. PTB7 and PTB7-Th are identical polymers except for the substitution of thiophene for oxygen in the pendant side chains attached to the benzodithiophene units (see Figure for chemical structures).…”

Photo-Carrier Multi-Dynamical Imaging at the Nanometer Scale in Organic and Inorganic Solar Cells

“…In solution-processed polymer or small-molecule bulk heterojunction (BHJ) solar cells, excitons are dissociated into free charges at the interfaces between electron donor (D) and acceptor (A) materials, which are processed to form interpenetrated networks phase-segregated at the 10 nm scale. Despite a tremendous amount of studies, the complex interplay between the D–A phases composition, interfaces morphology, photocarrier dynamics and transport remains intensively investigated. ,− It is also crucial to address how the photocarrier recombination can be impacted by grain boundaries, chemical impurities, and other local defects in polycrystalline or nanostructured films of silicon, , CdTe, CuInxGa (1– x ) Se 2 (CIGS), Cu 2 ZnSnS 4 (CZTS,) and hybrid organic–inorganic perovskites. , …”

Disentanglement of Degradation Mechanisms by Analyzing Aging Dynamics of Environmentally Friendly Processed Polymer Solar Cells

“…There might be some external or internal influences responsible for such degradation such as 1) a very intimate mixing of the donor and acceptor components upon aging, hampering the charge percolation, 2) hampered charge injection as well as extraction due to the formation of blocking layers near the electrodes by preferential segregation, and 3) photo-oxidation in the bulk material and interfacial oxidation at the electrodes via ingress of water and oxygen into the device (extrinsic degradation). [16,[39][40][41][42] Figure 5 shows the spectral response of PBDTTT-CT:PC 70 BM solar cells processed without (solid line) and with o-vanilline (dashed line). First of all, the additive red shifts the polymer contribution at from about 470 to about 500 nm, which remains stable against aging.…”

“…There might be some external or internal influences responsible for such degradation such as 1) a very intimate mixing of the donor and acceptor components upon aging, hampering the charge percolation, 2) hampered charge injection as well as extraction due to the formation of blocking layers near the electrodes by preferential segregation, and 3) photo‐oxidation in the bulk material and interfacial oxidation at the electrodes via ingress of water and oxygen into the device (extrinsic degradation). [ 16,39,40,41,42 ]…”