Recent progress in thick-film organic photovoltaic devices:Materials,devices,and processing

A successful transfer of organic photovoltaic technologies from lab to fab has to overcome a range of critical challenges such as developing high-mobility light-harvesting materials,minimizing the upscaling losses,designing advanced solar modules,controlling film quality,decreasing overall cost,and extending long-operation lifetime.To realize large-area devices toward practical applications,much effort has been devoted to understanding the fundamental mechanism of how molecular structures,device architectures,interfacial engineering,and light management and carrier dynamics affect photovoltaic performance.Such studies addressed various fundamental issues of charge carrier behavior in organic heterojunctions primarily in terms of exciton generation dependence upon light incidence,charge transportation dependence on built-in electric field,and charge extraction versus recombination.In consideration of high-throughput roll-to-roll process for large-scale fabrication of organic photovoltaic devices,it is highly appreciable to realize high power conversion efficiencies that are highly tolerable to the film thickness.Herein we summarize the recent progress in developing thick-film organic photovoltaic devices from the perspective of efficiency-loss mechanisms,material design,and device optimization strategies,proposing guidelines for designing high-efficiency thickness-insensitive devices toward mass production.

Deciphering the Origins of P1-Induced Power Losses in Cu(In_(x),Ga_(1–x))Se2(CIGS)Modules Through Hyperspectral Luminescence

In this report,we show that hyperspectral high-resolution photoluminescence mapping is a powerful tool for the selection and optimiz1ation of the laser ablation processes used for the patterning interconnections of subcells on Cu(Inx,Ga1-x)Se2(CIGS)modules.In this way,we show that in-depth monitoring of material degradation in the vicinity of the ablation region and the identification of the underlying mechanisms can be accomplished.Specifically,by analyzing the standard P1 patterning line ablated before the CIGS deposition,we reveal an anomalous emission-quenching effect that follows the edge of the molybdenum groove underneath.We further rationalize the origins of this effect by comparing the topography of the P1 edge through a scanning electron microscope(SEM)cross-section,where a reduction of the photoemission cannot be explained by a thickness variation.We also investigate the laser-induced damage on P1 patterning lines performed after the deposition of CIGS.We then document,for the first time,the existence of a short-range damaged area,which is independent of the application of an optical aperture on the laser path.Our findings pave the way for a better understanding of P1-induced power losses and introduce new insights into the improvement of current strategies for industry-relevant module interconnection schemes.

Solution-processed tandem organic solar cells

Organic solar cells(OSCs)show great potential in non-grid energy supply due to its unique properties including light-weight,flexibility,semi-transparency,design flexibility,low cost and so on.Thanks to researchers'tremendous efforts in materials development and device engineering,the power con-version efficiency(PCE)for single-junction OSCs(SJ-OSCs)has exceeded 18%[1,2].

High-performance all-polymer solar cells with only 0.47 eV energy loss

The field of all-polymer solar cells(all-PSCs)has experienced rapid development during the past few years,mainly driven by the development of efficient polymer acceptors.However,the power conversion efficiencies(PCEs)of the all-PSCs are still limited by insufficient light absorption of the donor/acceptor blend and large energy loss in devices.We herein designed a polymer acceptor PYT1 constructed n-type molecular acceptor Y5-C20 as the key building block and blended it with a polymer donor PM6 to obtain an all-polymer photoactive layer.The optimized PM6:PYT1 all-PSCs achieved a record higher PCE of 13.43%with a very low energy loss of 0.47 eV and a photoresponse of up to 900 nm compared with the Y5-C20 based device with a best PCE of 9.42%.Furthermore,the PCEs of the PM6:PYT1 all-PSCs are relatively insensitive to the 1-chloronaphthalene(CN)additive contents and active layer thickness.Our results also highlight the effect of CN additive on PM6:PYT1 morphology,i.e.,charge generation,and transport find an optimized balance,and radiative and non-radiative loss is simultaneously reduced in the blend.This work promotes the development of high-performance polymer acceptors and heralds a brighter future of all-PSCs for commercial applications.

Achieving Efficient Thick Film All-polymer Solar Cells Using a Green Solvent Additive

Adva nces in orga nic photovoltaic tech no logies have been geared toward industrial high-throughput printing manufacturing,which requires in sensitivity of photovoltaic performance reg a rd i ng to the light-harvesting layer thickness.However,the thickness of light-harvesti ng layer for all polymer solar cells(all-PSCs)is often limited to about 100 nm due to the dramatically decreased fill factor upon increasing film thickness,which hampers the light harvesting capability to in crease the power con versio n efficie ncy,and is un favorable for fabricating large-area devices.Here we dem on strate that by tuning the bulk heterojuncti on morphology using a non-halogenated solvent,cyclopentyl methyl ether,in the presence of a gree n solve nt additive of dibenzyl ether,the power con versio n efficie ncy of all-PSCs with photoactive layer thick nesses of over 500 nm reached an impressively high value of 9%.The gen eric applicability of this gree n solvent additive to boost the power conversion efficiency of thick-film devices is also validated in various bulk heterojunction active layer systems,thus representing a promising approach for the fabrication of all-PSCs toward industrial production,as well as further commercialization.

The fabrication of color-tunable organic light-emitting diode displays via solution processing

Electroluminescent devices based on organic semiconductors have attracted significant attention owing to their promising applications in flat-panel displays.The conventional display pixel consisting of side-by-side arrayed red,green and blue subpixels represents the mature technology but bears an intrinsic deficiency of a low pixel density.Constructing an individual color-tunable pixel that comprises vertically stacked subpixels is considered an advanced technology.Although color-tunable organic light-emitting diodes(OLEDs)have been fabricated using the vacuum deposition of small molecules,the solution processing of conjugated polymers would enable a much simpler and inexpensive manufacturing process.Here we present the all-solution processing of color-tunable OLEDs comprising two vertically stacked polymer emitters.A thin layer of highly conducting and transparent silver nanowires is introduced as the intermediate charge injection contact,which allows the emission spectrum and intensity of the tandem devices to be seamlessly manipulated.To demonstrate a viable application of this technology,a 4-by-4 pixelated matrix color-tunable display was fabricated.

Embedding physics domain knowledge into a Bayesian network enables layer-by-layer process innovation for photovoltaics

Process optimization of photovoltaic devices is a time-intensive,trial-and-error endeavor,which lacks full transparency of the underlying physics and relies on user-imposed constraints that may or may not lead to a global optimum.Herein,we demonstrate that embedding physics domain knowledge into a Bayesian network enables an optimization approach for gallium arsenide(GaAs)solar cells that identifies the root cause(s)of underperformance with layer-by-layer resolution and reveals alternative optimal process windows beyond traditional black-box optimization.Our Bayesian network approach links a key GaAs process variable(growth temperature)to material descriptors(bulk and interface properties,e.g.,bulk lifetime,doping,and surface recombination)and device performance parameters(e.g.,cell efficiency).For this purpose,we combine a Bayesian inference framework with a neural network surrogate device-physics model that is 100×faster than numerical solvers.With the trained surrogate model and only a small number of experimental samples,our approach reduces significantly the time-consuming intervention and characterization required by the experimentalist.As a demonstration of our method,in only five metal organic chemical vapor depositions,we identify a superior growth temperature profile for the window,bulk,and back surface field layer of a GaAs solar cell,without any secondary measurements,and demonstrate a 6.5%relative AM1.5G efficiency improvement above traditional grid search methods.

Branched side chains improve molecular packing of non-fullerene acceptors

As one of the promising emerging photovoltaic technologies(PVs),organic solar cells(OSCs)have received extensive attention from both scientific and industry communities.The advantages of OSCs,such as low toxicity,high power-toweight ratio,and easy manufacturing and upscaling,guarantee their contribution to versatile applications powered by clean and renewable solar energy,for instance.