Abstract
AbstractOpen‐circuit voltages of lead‐halide perovskite solar cells are improving rapidly and are approaching the thermodynamic limit. Since many different perovskite compositions with different bandgap energies are actively being investigated, it is not straightforward to compare the open‐circuit voltages between these devices as long as a consistent method of referencing is missing. For the purpose of comparing open‐circuit voltages and identifying outstanding values, it is imperative to use a unique, generally accepted way of calculating the thermodynamic limit, which is currently not the case. Here a meta‐analysis of methods to determine the bandgap and a radiative limit for open‐circuit voltage is presented. The differences between the methods are analyzed and an easily applicable approach based on the solar cell quantum efficiency as a general reference is proposed.
Highlights
Introduction mental data coexistIn particular in organic solar cells, the topic of comparing open-circuit voltages and referencing those toThe efficient conversion of solar radiation into electrical power different definitions of bandgap has been the subject by a solar cell requires absorbing the photons, creating charge of several recent publications.[7,8,9]carriers, collecting them at the junction and doing so atIn the case of the emerging technology of lead-halide a nonzero free energy per extracted charge carrier.[1,2,3] In order perovskites, the challenge of defining a bandgap initially to compare the ability of a solar cell to generate a high free seems less severe
We find that thanks to the sharp band edge and the small variations in Urbach tail slope, the radiative open-circuit voltage can always be determined for perovskite solar cells as long as an external photovoltaic quantum efficiency is available for a specific device
We find that if current highefficiency perovskite solar cells are compared with state-of-theart devices from other photovoltaic technologies, their resistive losses stand out as providing the highest potential for further improvement
Summary
The SQ model defines the maximum power-conversion efficiency of a solar cell consisting of a semiconducting absorber with a single bandgap EgSQ, using the basic thermodynamic principle of detailed balance.[16]. It is possible to use a measurement of the electroluminescence (EL) spectrum φEL(E) to obtain the missing values for the quantum efficiency of the solar cell for the low energy range and to combine them with the directly measured quantum efficiency QeEQE(E).[18,28] The extension of the photovoltaic quantum efficiency using electroluminescence data via Equation (6) has previously been used for perovskite solar cells[29,30] and other solution processable semiconductors.[31,32] in many cases only the bandgap or the bandgap derived is used.[12,13,14,33,34,35] Part of the reason for the absence of may be that the luminescence spectrum has to be measured with a setup that is at least calibrated for spectral shape (but not necessarily for absolute intensity) With this analysis we obtain two loss terms for the actual open-circuit voltage Voc, namely, the difference. This extended quantum efficiency can be obtained by applying the optoelectronic reciprocity theorem, which connects the electroluminescent emission of a solar cell with its photovoltaic quantum efficiency[24] and the voltage V via φEL exp qV kT (6)
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