• Energy Research

Light soaking under “1 sun” is performed on planar p–i–n perovskite solar cells with a Cs0.05MA0.10FA0.85Pb(I0.95Br0.05)3 absorber while measuring current and voltage transients simultaneously to spectral photoluminescence (PL). From theory a tenfold increase in PL intensity is expected for every 60 mV rise in VOC (at 300 K). However, the solar cells investigated show a reversible VOC increase from as low as 0.5 up to 1.05 V during light soaking, whereas the PL intensity hardly changes. A model is developed based on mobile ions in combination with a nonideal contact. It reproduces the decoupling of the VOC and PL as well as the transient behavior in great detail. Using state‐of‐the‐art materials and passivation layers shows that light soaking is still a relevant feature of high‐efficiency perovskite solar cells. The ionic liquid additive 1‐butyl‐3‐methylimidazolium tetrafluoroborate slows down the light‐soaking behavior, giving an example of how ionic motion in perovskite solar cells can be influenced.

This paper presents an alternative approach to obtain, from experimental measurements, physical parameters of organic solar cells associated with a given model. In order to get rid of the limitations of common fitting methods, we use a specific Markov chain Monte Carlo technique. This method is applied to a two-dimensional model of an organic solar cell. Measurements carried out under dark and one sun conditions, from two complementary cells, allow access to more reliable values of the active layer parameters. The corresponding set of parameters generates JV -curves in excellent agreement with the measurements for a range of different illumination intensities. Similar extractions are applied on temperature-dependent parameters, from experimental data acquired at various temperatures. As the simulation results reproduce the measurement data rather well, we show that this approach can also be useful to test or determine the governing law associated with some of the temperature-dependent parameters. In addition, analyzing the simulated responses of the model allows the identification of model limitations. The approach discussed in this paper, not specific to organic solar cells, can be applied to a large range of condensed matter topics.

In order to systematically improve perovskite-based solar cell technologies, it is crucial to identify performance limits and determine both global and local loss mechanisms quantitatively. One of the most important steps toward competitiveness is the upscaling of perovskite solar cells, which can be achieved, e.g., via solution-based blade coating processes. Cells with an active area of 1.1 cm² and efficiencies approaching 12% are presented and a comprehensive analysis based on spatially resolved measurements including photoluminescence, light beam-induced current, and dark lock-in thermography is demonstrated. We quantitatively reveal the losses of such solar cells by analyzing recombination, voltage, and pseudo-fill-factor losses across the whole cell area, correlate defects to individual process steps, and give an estimation of attainable efficiencies for improved solar cells without specific local defects.

Abstract An accurate electrical device characterization of hybrid organic-inorganic halide perovskite solar cells (PSCs) is an important prerequisite for further improvement and industrial transfer of this promising photovoltaic technology. In this work, we study the nonlinearity of current versus irradiance as well as the temperature dependence of PSCs in a spectrally resolved manner by highly accurate differential external quantum efficiency (EQE) measurements. We investigate three different types of PSCs fabricated by different research groups. The nonlinearity of all samples is found to be spectrally invariant, which significantly simplifies spectral mismatch corrections. We demonstrate that misinterpretation of EQE measurements can result in a more than 10% relative error in efficiency measurements, if solar simulators are adjusted to photocurrents determined from differential EQEs. For obtaining an accurate integrated photocurrent from EQEs, we introduce a new, convenient approach that accounts for cell nonlinearities but avoids the time-consuming full analysis of spectrally resolved nonlinearity. Moreover, for the samples investigated here, it is shown that the differential EQE measured at 0.35 suns bias irradiance represents a reasonably good estimate of the actual EQE at 1 sun. Furthermore, we determine spectrally resolved temperature coefficients (TCs) and show how the band gap blue shift varies with perovskite absorber and temperature.

Phenylguanidine, a strong ligand in the precursor solution, retards crystallization to enlarge grain sizes and reduce defect density of a perovskite film, demonstrating excellent universality across various compositions.

Abstract Highest published power conversion efficiencies of organic solar cells have mostly been achieved on substrates bearing a transparent indium tin oxide (ITO) electrode. However, the incorporation of ITO is not suited for future industrial production processes of organic solar cells, which will rely on a high-throughput of flexible substrates in order to achieve low cost of the final product. In this manuscript we present an alternative transparent electrode consisting of a layer stack of aluminum doped zinc oxide and a thin silver layer. Substrates with these electrodes have a transparency of above 75% in the wavelength range in which the photoactive layer absorbs light. Solar cells with a bulk-heterojunction of PTB7 and PC 71 BM in an inverted device architecture achieved a power conversion efficiency of 6.1%, which is the highest reported value for polymer solar cells free from both ITO and PEDOT:PSS. The sheet resistance of the novel electrodes increased only marginally after repeated bending which shows their full compatibility with future reel-to-reel processes or flexible products.

Abstract Silicon-based tandem solar cells can overcome the efficiency limit of single junction silicon solar cells. Perovskite solar cells are particularly promising as a top cell in monolithic tandem devices due to their rapid development towards high efficiencies, a tunable band gap with a sharp optical absorption edge and a simple production process. In monolithic tandem devices, the perovskite solar cell is deposited directly on the silicon cell, requiring low-temperature processes ( 2 ) scaffold - a structure yielding the highest efficiencies for single-junction perovskite solar cells. We show that evaporation of the compact TiO 2 hole blocking layer and ultra-violet (UV) curing for the mesoporous TiO 2 layer allows for good performance, comparable to high-temperature (> 500°C) processes. With both manufacturing routes, we obtain short-circuit current densities (J SC ) of about 20 mA/cm², open-circuit voltages (V OC ) over 1 V, fill factors (FF) between 0.7 and 0.8 and efficiencies (η) of more than 15%. We further show that the evaporated TiO 2 layer is suitable for the application in tandem devices. The series resistance of the layer itself and the contact resistance to an indium doped tin oxide (ITO) interconnection layer between the two sub-cells are low. In addition, the low parasitic absorption for wavelengths above the perovskite band gap allow a higher absorption in the silicon bottom solar cell, which is essential to achieve high tandem efficiencies.