A consistent mathematical approach is presented that connects the Shockley-Queisser (SQ) theory to the analysis of real-world devices. We demonstrate that the external photovoltaic quantum efficiency Q PV e of a solar cell results from a distribution of SQ-type band-gap energies and how this distribution is derived from experimental data. This leads us to the definition of a photovoltaic band-gap energy E PV g as a reference value for the analysis of the device performance. For a variety of solar-cell devices, we show that the combination of Q PV e and electroluminescence measurements allows for a detailed loss analysis that is fully compatible with the principle of detailed balance.

The success of recently discovered absorber materials for photovoltaic applications has been generating an increasing interest in systematic materials screening over the last years. However, the key for a successful materials screening is a suitable selection metric that goes beyond the Shockley-Queisser theory that determines the thermodynamic efficiency limit of an absorber material solely by its band gap energy. In this work, we develop a selection metric to quantify the potential photovoltaic efficiency of a material. Our approach is compatible with detailed balance and applicable in computational and experimental materials screening. We use the complex refractive index to calculate radiative and nonrradiative efficiency limits and the respective optimal thickness in the high mobility limit. We compare our model to the widely applied selection metric by Yu and Zunger [Phys Rev Lett 108, 068701 (2012)] with respect to their dependency on thickness, internal luminescence quantum efficiency and refractive index. Finally the model is applied to complex refractive indices calculated via electronic structure theory.2

CuSbS2 is a promising nontoxic and earth-abundant photovoltaic absorber that is chemically simpler than the widely studied Cu2ZnSnS4. However, CuSbS2 photovoltaic (PV) devices currently have relatively low efficiency and poor reproducibility, often due to suboptimal material quality and insufficient optoelectronic properties. To address these issues, here we develop a thermochemical treatment (TT) for CuSbS2 thin films, which consists of annealing in Sb2S3 vapor followed by a selective KOH surface chemical etch. The annealed CuSbS2 films show improved structural quality and optoelectronic properties, such as stronger band-edge photoluminescence and longer photoexcited carrier lifetime. These improvements also lead to more reproducible CuSbS2 PV devices, with performance currently limited by a large cliff-type interface band offset with CdS contact. Overall, these results point to the potential avenues to further increase the performance of CuSbS2 thin film solar cell, and the findings can be transferred to other thin film photovoltaic technologies.

We present a meaningful characterization method for tandem solar cells. The experimental method allows for optimizing the output power instead of the current. Furthermore, it enables the extraction of the approximate AM1.5g efficiency when working with noncalibrated spectra. Current matching of tandem solar cells under short-circuit condition maximizes the output current but is disadvantageous for the overall fill factor and as a consequence does not imply an optimization of the output power of the device. We apply the matching condition to the maximum power output; that is, a stack of solar cells is power matched if the power output of each subcell is maximal at equal subcell currents. The new measurement procedure uses additional light-emitting diodes as bias light in theJVcharacterization of tandem solar cells. Using a characterized reference tandem solar cell, such as a hydrogenated amorphous/microcrystalline silicon tandem, it is possible to extract the AM1.5g efficiency from tandems of the same technology also under noncalibrated spectra.

No abstract

No abstract

In thin-film tandem solar cells the sub cells are usually connected in series. The inherent current-limitation needs to be considered when optimizing the efficiency, but furthermore leads to challenges when comparing the sub cells performances of differently matched tandem cells. We have introduced the PowerMatching-Method that characterizes the device not only under one standard spectrum but under various spectral distributions. By this method, the same tandem cell can be characterized under various matching conditions. Based on simulations, we demonstrate a convenient way to compare differently matched tandem solar cells. Moreover, our simulations show that the method allows distinguishing between matching effects and changes in the sub-cells properties, e.g. changes due to the Staebler-Wronski-Effect.

No abstract