The external quantum efficiency (EQE), also known as incident-photon-to-collected-electron spectra are typically used to access the energy dependent photocurrent losses for photovoltaic devices. The integral over the EQE spectrum results in the theoretical short-circuit current under a given incident illumination spectrum. Additionally, one can also estimate the photovoltaic bandgap energy (Eg) from the inflection point in the absorption threshold region. The latter has recently been implemented in the "Emerging PV reports," where the highest power conversion efficiencies are listed for different application categories, as a function of Eg. Furthermore, the device performance is put into perspective thereby relating it to the corresponding theoretical limit in the Shockley–Queisser (SQ) model. Here, the evaluation of the EQE spectrum through the sigmoid function is discussed and proven to effectively report the Eg value and the sigmoid wavelength range λs, which quantifies the steepness of the absorption onset. It is also shown how EQE spectra with large λs indicate significant photovoltage losses and present the corresponding implications on the photocurrent SQ model. Similarly, the difference between the photovoltaic and optical bandgap is analyzed in terms of λs. ; O.A. acknowledges the financial support from the VDI/VD Innovation + Technik GmbH (Project-title: PV-ZUM), the SAOT funded by the German Research Foundation (DFG) in the framework of the German excellence initiative, and the Horizon 2020 project (grant number 871336-PEROXIS). J.G.C. gratefully acknowledges the financial support of the Deutscher Akademischer Austauschdienst (DAAD) through a doctoral scholarship. C.J.B. acknowledges funding from DFG within INST 90/917-1 FUGG, the SFB 953 (DFG, project no. 182849149) and the IGK 2495 (Energy Conversion Systems—from Materials to Devices). C.J.B. further acknowledges the grants "ELF-PV – Design and development of solution processed functional materials for the next generations of PV technologies" (No. 44–6521a/20/4) and "Solar Factory of the Future" (FKZ 20.2-3410.5-4-5) and the SolTech Initiative by the Bavarian State Government. Open access funding enabled and organized by Projekt DEAL.
AbstractA critical bottleneck for improving the performance of organic solar cells (OSC) is minimising non-radiative losses in the interfacial charge-transfer (CT) state via the formation of hybrid energetic states. This requires small energetic offsets often detrimental for high external quantum efficiency (EQE). Here, we obtain OSC with both non-radiative voltage losses (0.24 V) and photocurrent losses (EQE > 80%) simultaneously minimised. The interfacial CT states separate into free carriers with ≈40-ps time constant. We combine device and spectroscopic data to model the thermodynamics of charge separation and extraction, revealing that the relatively high performance of the devices arises from an optimal adjustment of the CT state energy, which determines how the available overall driving force is efficiently used to maximize both exciton splitting and charge separation. The model proposed is universal for donor:acceptor (D:A) with low driving forces and predicts which D:A will benefit from a morphology optimization for highly efficient OSC. ; N.G. acknowledges the Imperial College Research Fellowship scheme. C.J.B. gratefully acknowledge funding from the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation), Project no. 182849149-SFB 953. C.J.B. gratefully acknowledges financial support through the "Aufbruch Bayern" initiative of the state of Bavaria (EnCN and SFF) and the Bavarian Initiative "Solar Technologies go Hybrid" (SolTech) and funding from DFG project DFG INST 90/917. C.C.L. thanks the European Union for the financial support. G.C. acknowledges the support from the PRIN 2017 Project 201795SBA3—HARVEST.
Emerging photovoltaics (PVs) focus on a variety of applications complementing large scale electricity generation. Organic, dye-sensitized, and some perovskite solar cells are considered in building integration, greenhouses, wearable, and indoor applications, thereby motivating research on flexible, transparent, semitransparent, and multi-junction PVs. Nevertheless, it can be very time consuming to find or develop an up-to-date overview of the state-of-the-art performance for these systems and applications. Two important resources for recording research cells efficiencies are the National Renewable Energy Laboratory chart and the efficiency tables compiled biannually by Martin Green and colleagues. Both publications provide an effective coverage over the established technologies, bridging research and industry. An alternative approach is proposed here summarizing the best reports in the diverse research subjects for emerging PVs. Best performance parameters are provided as a function of the photovoltaic bandgap energy for each technology and application, and are put into perspective using, e.g., the Shockley–Queisser limit. In all cases, the reported data correspond to published and/or properly described certified results, with enough details provided for prospective data reproduction. Additionally, the stability test energy yield is included as an analysis parameter among state-of-the-art emerging PVs. ; O.A. acknowledges the financial support from the VDI/VD Innovation + Technik GmbH (Project-title: PV-ZUM) and the SAOT funded by the German Research Foundation (DFG) in the framework of the German excellence initiative. C.J.B. acknowledges funding from DFG within INST 90/917-1 FUGG, the SFB 953 (DFG, project no. 182849149) and the IGK 2495 (Energy Conversion Systems—from Materials to Devices). C.J.B. further acknowledges the grants "ELF-PV—Design and development of solution processed functional materials for the next generations of PV technologies" (No. 44-6521a/20/4) and "Solar Factory of the Future" (FKZ 20.2-3410.5-4-5) and the SolTech Initiative by the Bavarian State Government. A.F.N. acknowledges support from FAPESP (Grant 2017/11986-5), Shell and the strategic importance of the support given by ANP (Brazil's National Oil, Natural Gas and Biofuels Agency) through the R&D levy regulation. R.R.L. gratefully acknowledges support from the National Science Foundation under grant CBET-1702591. N.K. acknowledges funding by the US Department of Energy, Office of Energy Efficiency and Renewable Energy, Solar Energy Technologies Office, Agreement Number 34351. J.N. thanks the European Research Council for support under the European Union's Horizon 2020 research and innovation program (grant agreement No 742708).
Improving the long-term stability of perovskite solar cells is critical to the deployment of this technology. Despite the great emphasis laid on stability-related investigations, publications lack consistency in experimental procedures and parameters reported. It is therefore challenging to reproduce and compare results and thereby develop a deep understanding of degradation mechanisms. Here, we report a consensus between researchers in the field on procedures for testing perovskite solar cell stability, which are based on the International Summit on Organic Photovoltaic Stability (ISOS) protocols. We propose additional procedures to account for properties specific to PSCs such as ion redistribution under electric fields, reversible degradation and to distinguish ambient-induced degradation from other stress factors. These protocols are not intended as a replacement of the existing qualification standards, but rather they aim to unify the stability assessment and to understand failure modes. Finally, we identify key procedural information which we suggest reporting in publications to improve reproducibility and enable large data set analysis. ; This article is based upon work from COST Action StableNextSol MP1307 supported by COST (European Cooperation in Science and Technology). M.V.K., E.A.K., V.B. and A.O. thank the financial support of the United States – Israel Binational Science Foundation (grant no. 2015757). E.A.K., A.A. and I.V.-F. acknowledge partial support from the SNaPSHoTs project in the framework of the German-Israeli bilateral R&D cooperation in the field of applied nanotechnology. M.S.L. thanks the financial support of National Science Foundation (ECCS, award #1610833). S.C., M.Manceau and M.Matheron thank the financial support of European Union's Horizon 2020 research and innovation programme under grant agreement no 763989 (APOLO project). F.D.R. and T.M.W. would like to acknowledge the support from the Engineering and Physical Sciences Research Council (EPSRC) through the SPECIFIC Innovation and Knowledge Centre (EP/N020863/1) and express their gratitude to the Welsh Government for their support of the Ser Solar programme. P.A.T. acknowledges financial support from the Russian Science Foundation (project No. 19-73-30020). J.K. acknowledges the support by the Solar Photovoltaic Academic Research Consortium II (SPARC II) project, gratefully funded by WEFO. M.K.N. acknowledges financial support from Innosuisse project 25590.1 PFNM-NM, Solaronix, Aubonne, Switzerland. C.-Q.M. would like to acknowledge The Bureau of International Cooperation of Chinese Academy of Sciences for the support of ISOS11 and the Ministry of Science and Technology of China for the financial support (no. 2016YFA0200700). N.G.P. acknowledges financial support from the National Research Foundation of Korea (NRF) grants funded by the Ministry of Science, ICT Future Planning (MSIP) of Korea under contracts NRF-2012M3A6A7054861 and NRF-2014M3A6A7060583 (Global Frontier R&D Program on Center for Multiscale Energy System). CSIRO's contribution to this work was conducted with funding support from the Australian Renewable Energy Agency (ARENA) through its Advancing Renewables Program. A.F.N gratefully acknowledges support from FAPESP (Grant 2017/11986-5) and Shell and the strategic importance of the support given by ANP (Brazil's National Oil, Natural Gas and Biofuels Agency) through the R&D levy regulation. Y.-L.L. and Q.B. acknowledge support from the National Science Foundation Division of Civil, Mechanical and Manufacturing Innovation under award no. 1824674. S.D.S. acknowledges the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (HYPERION, grant agreement no. 756962), and the Royal Society and Tata Group (UF150033). The work at the National Renewable Energy Laboratory was supported by the US Department of Energy (DOE) under contract DE-AC36-08GO28308 with Alliance for Sustainable Energy LLC, the manager and operator of the National Renewable Energy Laboratory. The authors (J.J.B, J.M.L., M.O.R, K.Z.) acknowledge support from the 'De-risking halide perovskite solar cells' program of the National Center for Photovoltaics, funded by the US Department of Energy, Office of Energy Efficiency and Renewable Energy, Solar Energy Technology Office. The views expressed in the article do not necessarily represent the views of the DOE or the US Government. H.J.S. acknowledges the support of EPSRC UK, Engineering and Physical Sciences Research Council. V.T. and M.Madsen acknowledge 'Villum Foundation' for funding of the project CompliantPV, under project no. 13365. M.Madsen acknowledges Danmarks Frie Forskningsfond, DFF FTP for funding of the project React-PV, no. 8022-00389B. M.G. and S.M.Z. thank the King Abdulaziz City for Science and technology (KACST) for financial support. S.V. acknowledges TKI-UE/Ministry of Economic Affairs for financial support of the TKI-UE toeslag project POP-ART (no. 1621103). RC thanks the grants for Development of New Faculty Staff, Ratchadaphiseksomphot Endowment Fund. A.D.C. gratefully acknowledges funding from the European Union's Horizon 2020 Research and Innovation Program (grant agreement no. 785219-GrapheneCore2 and no. 764047-ESPResSo). M.L.C. and H.X. acknowledges the support from Spanish MINECO for the grant GraPErOs (ENE2016-79282-C5-2-R), the OrgEnergy Excellence Network CTQ2016-81911- REDT, the Agència de Gestiód'Ajuts Universitaris i de Recerca (AGAUR) for the support to the consolidated Catalonia research group 2017 SGR 329 and the Xarxa de Referència en Materials Avançats per a l'Energia (Xarmae). ICN2 is supported by the Severo Ochoa program from Spanish MINECO (Grant no. SEV-2017-0706) and is funded by the CERCA Programme/Generalitat de Catalunya. ; Peer reviewed
