Multi-Source/Component Spray Coating for Polymer Solar Cells

Abstract

A multi-source/component spray coating process to fabricate the photoactive layers in polymer solar cells is demonstrated. Well-defined domains consisting of polymer:fullerene heterojunctions are constructed in ambient conditions using an alternating spray deposition method. This approach preserves the integrity of the layer morphology while forming an interpenetrating donor (D)/acceptor (A) network to facilitate charge transport. The formation of multi-component films without the prerequisite of a common solvent overcomes the limitations in conventional solution processes for polymer solar cells and enables us to process a wide spectrum of materials. Polymer solar cells based on poly(3-hexylthiophene):[6,6]-phenyl C(61) butyric acid methyl ester spray-coated using this alternating deposition method deliver a power conversion efficiency of 2.8%, which is comparable to their blend solution counterparts. More importantly, this approach offers the versatility to independently select the optimal solvents for the donor and acceptor materials that will deliver well-ordered nanodomains. This method also allows the direct stacking of multiple photoactive polymers with controllable absorption in a tandem structure even without an interconnecting junction layer. The introduction of multiple photoactive materials through multisource/component spray coating offers structural flexibility and tenability of the photoresponse for future polymer solar cell applications.

Fundamental Study on the Effect of Spray Parameters on Characteristics of P3HT:PCBM Active Layers Made by Spray Coating

“…In a similar series of images, Figure 6 shows the effect of carrier air pressure on the film morphology for the films deposited using a single spray pass. In images shown in Figures 5 and 6, atop the P3HT:PCBM film, stacked disk-like splats are observed, a phenomenon which is often observed in similar works, e.g., [26][27][28][30][31][32][33][34][35][36][37][38]. Spray droplets impact the substrate by aid of the carrier air, spread on the substrate, and if the precursor flow rate is high enough, the substrate is wettable, and the drying time is long enough, droplets may merge or coalesce, forming a liquid film and a thin solid film after solvent evaporation.…”

“…The PCEs of spray-on devices based on P3HT: PCBM are usually around 2%-3%, lower than those of devices made by spin coating [26][27][28][29][30][31][32][33][34][35][36][37]. This is because, the typical spray-on films are not uniform and under unfavorable spraying conditions may consist of stacks of dried solution droplets or so-called splats [26][27][28][30][31][32][33][34][35][36][37][38]. Also, the lower PCEs of the spray-on devices may be attributed to excessive roughness, although the device performance is seemingly more related to the film nano-structure, which requires adequate process understanding and controlling.…”

The Critical Role of Processing and Morphology in Determining Degradation Rates in Polymer Solar Cells

“…The obtained decay was as reported earlier in literature. [ 42 ] A mono-exponential decay function ( Δ OD = At − α , where A is the pre-exponential function, t the time and α the power law component) was used to fi t the decay.…”

Connecting physical properties of spin-casting solvents with morphology, nanoscale charge transport, and device performance of poly(3-hexylthiophene):phenyl-C₆₁-butyric acid methyl ester bulk heterojunction solar cells

“…24,45,46 Different physical properties of CB and 1,2-DCB are summarized in Table 1. Fullerene is less soluble in CB than in 1,2-DCB, 47 and larger clusters of PCBM in CB-based films may be a result of poor solubility leading to early precipitation of PCBM during solvent evaporation, especially during the thermal annealing process when the residual solvent evaporates quickly from the blend.…”