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Tandem structure provides a practical way to realize high efficiency organic photovoltaic cells, it can be used to extend the wavelength coverage for light harvesting. The interconnecting layer (ICL) between subcells plays a critical role in the reproducibility and performance of tandem solar cells, yet the processability of the ICL has been a challenge. In this work the fabrication of highly reproducible and efficient tandem solar cells by employing a commercially available material, PEDOT:PSS HTL Solar (HSolar), as the hole transporting material used for the ICL is reported. Comparing with the conventional PEDOT:PSS Al 4083 (c‐PEDOT), HSolar offers a better wettability on the underlying nonfullerene photoactive layers, resulting in better charge extraction properties of the ICL. When FTAZ:IT‐M and PTB7‐Th:IEICO‐4F are used as the subcells, a power conversion efficiency (PCE) of 14.7% is achieved in the tandem solar cell. To validate the processability of these tandem solar cells, three other research groups have successfully fabricated tandem devices using the same recipe and the highest PCE obtained is 16.1%. With further development of donor polymers and device optimization, the device simulation results show that a PCE > 22% can be realized in tandem cells in the near future. [ABSTRACT FROM AUTHOR]

'Nonfullerene' acceptors are proving effective in bulk heterojunction (BHJ) solar cells when paired with selected polymer donors. However, the principles that guide the selection of adequate polymer donors for high-efficiency BHJ solar cells with nonfullerene acceptors remain a matter of some debate and, while polymer main-chain substitutions may have a direct influence on the donor-acceptor interplay, those effects should be examined and correlated with BHJ device performance patterns. This report examines a set of wide-bandgap polymer donor analogues composed of benzo[1,2- b:4,5- b′]dithiophene (BDT), and thienyl ([2H]T) or 3,4-difluorothiophene ([2F]T) motifs, and their BHJ device performance pattern with the nonfullerene acceptor 'ITIC'. Studies show that the fluorine- and ring-substituted derivative PBDT(T)[2F]T largely outperforms its other two polymer donor counterparts, reaching power conversion efficiencies as high as 9.8%. Combining several characterization techniques, the gradual device performance improvements observed on swapping PBDT[2H]T for PBDT[2F]T, and then for PBDT(T)[2F]T, are found to result from (i) notably improved charge generation and collection efficiencies (estimated as ≈60%, 80%, and 90%, respectively), and (ii) reduced geminate recombination (being suppressed from ≈30%, 25% to 10%) and bimolecular recombination (inferred from recombination rate constant comparisons). These examinations will have broader implications for further studies on the optimization of BHJ solar cell efficiencies with polymer donors and a wider range of nonfullerene acceptors. [ABSTRACT FROM AUTHOR]

Organic Solar Cells: High-Performance Tandem Organic Solar Cells Using HSolar as the Interconnecting Layer (Adv. Keywords: interconnecting layers; organic photovoltaics; tandem solar cells EN interconnecting layers organic photovoltaics tandem solar cells 1 1 1 07/09/20 20200707 NES 200707 In article number 2000823, Carr Hoi Yi Ho, Franky So and co-workers presented a simple yet highly compatible interconnecting layer for organic tandem solar cells. In addition, most of the tandem devices achieve more than 40% enhancement from the single-junction solar cell. [Extracted from the article]