Blade-coating serving as a prototype tool for slot-die coating can be very compatible with large-area roll-to-roll coating. Using blade-coating in an ambient environment, an average power conversion efficiency (PCE) of 10.03% is achieved in nonfullerene organic solar cells, which is higher than that of the optimal spin-coated device with a PCE of 9.41%. It is demonstrated that blade-coating can induce a higher degree of molecular packing for both conjugated polymer donors and small-molecular acceptors as it helps to produce a seeding film containing numerous crystal grains, subsequently providing nucleation sites for the residual solution when the motion of the blade exposes a liquid front. Due to this effect, blade-coating can partially replace the role of the additive 1,8-diiodooctane (DIO) and thus achieves the optimized morphology with fewer additives. Moreover, it is found that the blade-coated film with 0.25% DIO possesses not only a smaller domain size but also higher domain purity, suggesting more D/A (donor/acceptor) interfaces and a purer phase domain as compared to the spin-coated film with 1% DIO. Encouragingly, the blade-coated device with less DIO (0.25%) exhibits much better stability than the spin-coated device with 1% DIO, showing excellent prospects.
As a prototype tool for slot‐die coating, blade‐coating exhibits excellent compatibility with large‐area roll‐to‐roll coating. A ternary organic solar cell based on PBDB‐T:PTB7‐Th:FOIC blends is fabricated by blade‐coating and exhibits a power conversion efficiency of 12.02%, which is one of the highest values for the printed organic solar cells in ambient environment. It is demonstrated that blade‐coating can enhance crystallization of these three materials, but the degree of induction is different (FOIC > PBDB‐T > PTB7‐Th). Thus, the blade‐coated PBDB‐T:FOIC device presents much higher electron mobility than hole mobility due to the very high crystallinity of FOIC. Upon the addition of PTB7‐Th into the blade‐coated PBDB‐T:FOIC blends, the crystallinity of FOIC decreases together with the corresponding electron mobility, due to the better miscibility between PTB7‐Th and FOIC. The ternary strategy not only maintains the well‐matched crystallinity and mobilities, but also increases the photocurrent with complementary light absorption as well as the Förster resonant energy transfer. Furthermore, small domains with homogeneously distributed nanofibers are observed in favor of the exciton dissociation and charge transport. This combination of blade‐coating and ternary strategies exhibits excellent synergistic effect in optimizing morphology, showing great potential in the large‐area fabrication of highly efficient organic solar cells.
The progress in efficiency improvements of blade-coated two-dimensional perovskite solar cells (PSCs) lags behind that of spin-coated ones. Pinholes and voids are two important structural defects hiding in blade-coated large-area perovskite films to deteriorate device efficiency and stability. However, the formation of pinholes and voids is still difficult to predict. On substrates with moderate wettability, Dion–Jacobson perovskite films can be blade-coated with good coverage, but we highlight that the formation of nanoscale voids buried at the bottom side of perovskite films can occur frequently, depending critically on the wettability of substrates. It is revealed that super hydrophilic NiOx substrates with contact angle θ < 5° possesses strong bubble repellent property, which thermal dynamically prevents the retraction of precursor solution and plays an important role to suppress the attachment and growth of bubbles on its surface. The probabilities of forming both pinholes and buried voids in perovskite films on super hydrophilic NiOx substrates are one order of magnitude lower than that on hydrophilic PTAA and poly-TPD substrates. The blade-coated (BDA)MA4Pb5I16 films on NiOx substrate offer PSCs with excellent interfacial hole extraction and reduced leakage current, contributing a significant power conversion efficiency improvement from ∼10% to 16.26%.
Organic solar cells (OSC) have great potential for flexible and wearable electronics due to their significant energy supply. However, the brittleness of inorganic electron transport layers (ETL) and their large-area production make it difficult to use them in flexible inverted OSCs. Herein, an organic–inorganic hybrid cathode interlayer of incorporating poly(4-vinylphenol) (P4VP) into the ZnO precursor solution was developed. The addition of P4VP improves the conductibility of ETL and facilitates the favorable vertical component distribution of active layer on the ZnO:P4VP substrate. Thus, the blade-coated OSC based on ZnO:P4VP performs better than the ZnO-based OSC in terms of photovoltaic performance and thickness insensitivity. The P4VP acts as an adhesive in ZnO grain boundaries and eliminates cracks in the bent ETL, leading to a significantly improved mechanical flexibility. Consequently, the ZnO:P4VP-based large-area flexible OSC achieves a power conversion efficiency of 14.05% and retains 80% of its initial efficiency after 1000 bending cycles, which is much better than that based on pristine ZnO (12.26%, 44%). Furthermore, flexible inverted organic solar modules were fabricated and achieved a considerable efficiency of 12.01%. These findings provide a general approach for using inorganic materials in flexible and wearable electronics.
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