High‐Performance and Stable All‐Polymer Solar Cells Using Donor and Acceptor Polymers with Complementary Absorption

Abstract

To explore the advantages of emerging all‐polymer solar cells (all‐PSCs), growing efforts have been devoted to developing matched donor and acceptor polymers to outperform fullerene‐based PSCs. In this work, a detailed characterization and comparison of all‐PSCs using a set of donor and acceptor polymers with both conventional and inverted device structures is performed. A simple method to quantify the actual composition and light harvesting contributions from the individual donor and acceptor is described. Detailed study on the exciton dissociation and charge recombination is carried out by a set of measurements to understand the photocurrent loss. It is unraveled that fine‐tuned crystallinity of the acceptor, matched donor and acceptor with complementary absorption and desired energy levels, and device architecture engineering can synergistically boost the performance of all‐PSCs. As expected, the PBDTTS‐FTAZ:PNDI‐T10 all‐PSC attains a high and stable power conversion efficiency of 6.9% without obvious efficiency decay in 60 d. This work demonstrates that PNDI‐T10 can be a potential alternative acceptor polymer to the widely used acceptor N2200 for high‐performance and stable all‐PSCs.

8.0% Efficient All‐Polymer Solar Cells with High Photovoltage of 1.1 V and Internal Quantum Efficiency near Unity

“…The PBDTS-TPD:PNDI-T all-PSC shows a slightly lower η BR of 4.2% than that of 5.3% for the PBDT-TPD:PNDI-T all-PSC. In fact, these η BR values are relatively small as compared to our previous reports, [24,36,41] indicating that only negligible bimolecular recombination occurs at the short-circuit condition in the two all-PSCs. Importantly, we have to point out that bimolecular recombination usually becomes more agitated at the maximum power point of solar cells, which can be one of the key factors that constrains the photocurrent at the maximum power point in this work.…”

“…The geminate recombination loss can be estimated from η G = 1 − (J sat /J max ). [41] In this case, it can be concluded that the geminate recombination in both the all-PSCs is negligible at the short-circuit condition, where the PBDTS-TPD:PNDI-T all-PSC presents a lower η G of ≈0.8%, compared to the PBDT-TPD:PNDI-T all-PSC with a η G of ≈3.1%. It reflects that almost all the generated excitons in the PBDTS-TPD:PNDI-T films can efficiently diffuse to the D/A interface and dissociate into free charges, which is associated with the high quenching efficiencies and the more desired morphology of the PBDTS-TPD:PNDI-T blend.…”

“…High η A over 73% are also recorded from the acceptor PNDI-T in the two polymer:polymer blends, which are superior to the η A of the acceptor polymers that we measured in several all-PSC systems. [24,41] Since the donor polymers do emit and contribute to the quantum yield in each blend film, we should point out that the actual η A should be higher than these minimal values. Both the high η D and η A reveal that the generated excitons in both the donor and acceptor polymers can dissociate efficiently in each of the two polymer:polymer blends, which are in reasonable agreement with the high internal quantum efficiency (IQE), as we discuss in the next section.…”

“…In both solution and thin films, much higher absorption coefficients are recorded for the two donor polymers as compared to the acceptor, implying that the two donor polymers contribute more to light absorption ( Figure S3, Supporting Information). [41] Compared to PBDT-TPD, PBDTS-TPD presents slightly broader absorption spectrum with a higher absorption coefficient in almost the whole absorption wavelength. This is probably due to the linear alkylthio side chains, which can promote the packing of polymer chains.…”

“…[72,73] Recently, we have successfully used this method to quantify bimolecular recombination in some all-PSCs. [24,36,41] In this scenario, the EQE responses with and without illumination of a bias light (530 nm) were measured ( Figure S14, Supporting Information). The PBDTS-TPD:PNDI-T all-PSC shows a slightly lower η BR of 4.2% than that of 5.3% for the PBDT-TPD:PNDI-T all-PSC.…”