Improving, characterizing and predicting the lifetime of organic photovoltaics

Abstract

This review summarizes the recent progress in the stability and lifetime of organic photovoltaics (OPVs). In particular, recently proposed solutions to failure mechanisms in different layers of the device stack are discussed comprising both structural and chemical modifications. Upscaling is additionally discussed from the perspective of stability presenting the challenges associated with device packaging and edge protection. An important part of device stability studies is the characterization and the review provides a short overview of the most advanced techniques for stability characterization reported recently. Lifetime testing and determination is another challenge in the field of organic solar cells and the final chapters discuss the testing protocols as well as the generic marker for device lifetime and the methodology for comparing all the lifetime landmarks in one common diagram. These tools were used to determine the baselines for OPV lifetime tested under different ageing conditions. Finally, the current status of lifetime for organic solar cells is presented and predictions are made for the progress in near future.

Impact of P3HT materials properties and layer architecture on OPV device stability

“…Various published reports demonstrated extrapolated operational lifetimes of OPV for several years 4,5,7,8,11 . A recently published review 3,6,9 revealed an increase in publication activities on OPV stability research and an increase in average reported lifetimes over the recent years, clearly demonstrating progress in the field. The observed experimental lifetimes range up to 2 years 8,10 , when no extrapolations to T80 (corresponding to efficiency drop to 80% of the initial efficiency value) or TS,80 (corresponding to efficiency drop to 80% after stabilization) were considered 11,12 .…”

“…Power conversion efficiencies of 13-14% were obtained in single junction, bulk-heterojunction organic solar cells (BHJ OSC) 1,2 and operational lifetimes in the range of 10 years [3][4][5] were estimated on the basis of exclusively intrinsic degradation processes. Roll-to-roll processed flexible modules have already demonstrated outdoor stabilities of several years 6 . While this is very encouraging and promising, more understanding is required in terms of how materials properties impact the device stability.…”

“…Transport layers can be quite diverse, ranging from small molecules to polymers to amorphous or nanocrystalline metal oxides to hybrids of these materials 41 . A commonly used hole transport layer, PEDOT:PSS, is well known to be a potential weak point for stability, due to its hygroscopic and acidic properties 6,42 . Metal oxides have become very common as transport layers due to their capability to be solution processable 36 and their rather good stability 37,[43][44][45] .…”

“…The most commonly studied material in OPV is poly(3-hexylthiophene) (P3HT) 46 , as it is relatively cheap to produce and readily available in kilogram amounts, due to easy synthetic upscaling 47 . In order to enable wide comparability among the researchers working in the field, in this study solar cells based on the classical material combination P3HT:PCBM ( [6,6]-phenyl-C61butyric acid methyl ester) were explored under variation of P3HT batches in order to assess the impact of the material parameters of P3HT on device stability. Five labs were involved in providing solar cells according to their optimized layer stack architecture and device layout, constituting the second parameter space.…”

Insights into the Failure Mechanisms of Organic Photodetectors

“…[12]- [15] To date, the lifetime of organic solar cells, defined by Ts80, [16] reached 10,000 hours (417 days), [17] [18] and the main limitation is currently attributed to a low power conversion efficiency of the organic cell.…”