Quantifying the Absorption Onset in the Quantum Efficiency of Emerging Photovoltaic Devices

Abstract

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.