Optical Optimization of Thin-Film Polymer Solar Cells

Tiwari, Sanjay; Gebauer, Ralph

doi:10.1007/978-981-15-6116-0_17

Cited by 1 publication

(1 citation statement)

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“…[92,93] Reflection and interference (both constructive and destructive) by the metal electrodes (more so for vacuum deposited than printed electrodes) as well as by electron/holetransport layers, mostly affect thinner films while they show no significant influence on the thicker ones (>300 nm), which usually exhibit saturation in absorption and consequently in short-circuit current (J sc ). The strong J sc dependence on the optical effects, derived from the active-layer thickness, limits the choice of materials, the range of employable thicknesses, as well as the usable printing techniques for electrodes and interfaces required to fully solution process OPV devices; [93,94] ii) Thickness coating window: Tight precision is required when coating/printing OPV active layer materials that must be thin (≈100 nm), due to low charge mobilities), as a small delta can greatly influence performance through the fill factor (FF) dependence on thickness. The higher charge mobilities exhibited by OPV active-layer materials that can be coated thicker-with the fill factor being not significantly affected by thickness change-allows for a broader process window in terms of precision during coating/printing; iii) Shunt resistance: Thick films allow for better shunt resistance, especially in large-area devices.…”

Section: Thickness Requirements For Printabilitymentioning

confidence: 99%

Polymer Solar Cells with Active Layer Thickness Compatible with Scalable Fabrication Processes: A Meta‐Analysis

et al. 2023

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a series of reasons. First of all, the power conversion efficiencies (PCEs) are still low compared to silicon photovoltaics or perovskite photovoltaics. At the laboratory level, the PCEs of small area devices are improving, [9] but with their best still below 20%, [10,11] despite the fact that the recent breakthrough discovery of non-fullerene acceptors (NFAs) [12,13] has almost doubled the values achieved within the last four years. Second, although important progress on controlling degradation has been made, [14] the device stability still needs to be improved to provide reliable and marketable products. Third, the synthetic complexity [15][16][17][18] of the best performing active layer materials (both donor and acceptors) is usually relatively high, which translates into high material's production costs. Fourth, the interfacial engineering is still at the research stage [19] and a defined scalable device architecture has not yet been fully established. Last, but not least, the scalability of cells to modules with continuous printing/coating techniques has been demonstrated, [20,21] but in practice, formulating the active inks at an industrial level is not an easy task. Problems related to photoactive materials solubility, solution viscosities, and films' wettability have to be carefully approached to achieve optimal process conditions, suitable for roll-to-roll (R2R) manufacturing.One issue in particular is worth considering: to achieve homogeneous, pinhole-free film over large areas and at high printing speed, the active-layer thickness needs to be high enough. A thickness above 200 nm is considered suitable, [22,23] but this point is in conflict with the possibility for the charge carriers to effectively reach the electrode contacts while avoiding recombinations. Charge-carrier mobilities of organic semiconductors are in fact not very high, even in the best of cases. It is known that optimal PCEs of NFA-based polymer solar cells are achieved with thicknesses of around 90-120 nm, [24] and then decrease when thickness is increased (Figure 1). Together with the limitations in annealing temperatures and durations, the need to substitute evaporated interlayers and electrodes with printable alternatives and the need for a high thickness of the active (absorbing) layer is one of the main reasons for the PCE decrease in the transition from small-area laboratory devices to large-area modules by R2R processes.Organic photovoltaics (OPV) has been considered for a long time a promising emerging solar technology. Currently, however, market shares of OPV are practically non-existent. A detailed meta-analysis of the literature published until mid-2021 is presented, focusing on one of the remaining issues that need to be addressed to translate the recent remarkable progress, obtained in devices' performance at lab-scale level, into the requirements able to boost the manufacturing-scale production. Namely, the active layer's thickness is referred to, which, together with device efficiency and stability, represents one of th...

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