The energy costs associated with separating tightly bound excitons (photoinduced electron-hole pairs) and extracting free charges from highly disordered low-mobility networks represent fundamental losses for many low-cost photovoltaic technologies. We report a low-cost, solution-processable solar cell, based on a highly crystalline perovskite absorber with intense visible to near-infrared absorptivity, that has a power conversion efficiency of 10.9% in a single-junction device under simulated full sunlight. This "meso-superstructured solar cell" exhibits exceptionally few fundamental energy losses; it can generate open-circuit photovoltages of more than 1.1 volts, despite the relatively narrow absorber band gap of 1.55 electron volts. The functionality arises from the use of mesoporous alumina as an inert scaffold that structures the absorber and forces electrons to reside in and be transported through the perovskite.

https://science.sciencemag.org/content/sci/early/2012/10/03/science.1228604.full.pdf

Efficient Hybrid Solar Cells Based on Meso-Superstructured Organometal Halide Perovskites

Dye-sensitized solar cells (DSCs) offer the possibilities to design solar cells with a large flexibility in shape, color, and transparency. DSC research groups have been established around the worl ...

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Dye-Sensitized Solar Cells

Many different photovoltaic technologies are being developed for large-scale solar energy conversion. The wafer-based first-generation photovoltaic devices have been followed by thin-film solid semiconductor absorber layers sandwiched between two charge-selective contacts and nanostructured (or mesostructured) solar cells that rely on a distributed heterojunction to generate charge and to transport positive and negative charges in spatially separated phases. Although many materials have been used in nanostructured devices, the goal of attaining high-efficiency thin-film solar cells in such a way has yet to be achieved. Organometal halide perovskites have recently emerged as a promising material for high-efficiency nanostructured devices. Here we show that nanostructuring is not necessary to achieve high efficiencies with this material: a simple planar heterojunction solar cell incorporating vapour-deposited perovskite as the absorbing layer can have solar-to-electrical power conversion efficiencies of over 15 per cent (as measured under simulated full sunlight). This demonstrates that perovskite absorbers can function at the highest efficiencies in simplified device architectures, without the need for complex nanostructures.

Efficient planar heterojunction perovskite solar cells by vapour deposition

Within the space of a few years, hybrid organic–inorganic perovskite solar cells have emerged as one of the most exciting material platforms in the photovoltaic sector. This review describes the rapid progress that has been made in this area.

The emergence of perovskite solar cells

Organic electronics are beginning to make significant inroads into the commercial world, and if the field continues to progress at its current, rapid pace, electronics based on organic thin-film materials will soon become a mainstay of our technological existence. Already products based on active thin-film organic devices are in the market place, most notably the displays of several mobile electronic appliances. Yet the future holds even greater promise for this technology, with an entirely new generation of ultralow-cost, lightweight and even flexible electronic devices in the offing, which will perform functions traditionally accomplished using much more expensive components based on conventional semiconductor materials such as silicon.

The path to ubiquitous and low-cost organic electronic appliances on plastic

Measurement techniques which rely on the exact knowledge of the actual generation rate within a silicon sample (such as quasi-steady-state photoconductance measurements) are significantly affected by spectral variations of the illumination source. This is especially the case when using supplementary long-pass filters, in order to ensure a more symmetrical excess carrier profile within low- lifetime silicon samples. In this contribution the effect of different illumination spectra on photoconductance-based lifetime measurements will be investigated in detail. The calculations are based on actual measurements of the optical properties of the samples and the reference cell, as well as the used photo flash spectra. Two different simple approaches to calculate the excess carrier generation rate are presented and compared. Evaluations are exemplarily performed on a set of unpassivated thickness- varied silicon samples, revealing generation rate deviations as high as 21 % for different sample thicknesses and illumination spectra. Additionally, the effect of the different excitation spectra on the measured effective lifetime will be shown.

Photoconductance-Based Excess Carrier Lifetime Measurements on Unpassivated Silicon Samples

The economical relevance of a shift of several percent in the produced output of a PV factory is obvious. Basic for the assessment of cell performance in the cell sorter measurements at the end of a production line are calibrated references. We report on the leading-edge achievements of a cooperation project between most relevant German cell and test equipment manufacturers with Fraunhofer ISE CalLab PV Cells and the PTB in this research field. A significant reduction in the uncertainty of the calibration of large area industrial cells without cell inter-connectors has been achieved. Uncertainty in the short circuit current was reduced from previously 2.5 % to now 1.8 %. A series of measures to assure long term comparability of calibration results was established. Criteria for the selection of reference cells were agreed upon. Optical features of industrial cell testers were assessed on the basis of a complete uncertainty calculation for the attribution to a simulator class. Some progress steps in the complex metrology of a light sensitive device are exemplified in the paper.

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Precise Measurement of Solar Cell Performance in Production

Illuminated Lock-In Thermography (ILIT) is a versatile tool for spatially resolved detection of power losses in silicon solar cells close to real operation conditions. In this paper, quantitative analysis of different power loss mechanisms contributing to the ILIT-signal will be presented by means of ILIT-measurements. First, the appearance of heat due to energy losses of free carriers after photon absorption and energy losses of carriers crossing the p-n-junction will be verified in ILIT-measurements. Further, two different methods of quantifying ohmic type shunts with ILIT-measurements will be compared. It will be shown, that it is possible to determine a reliable global value for the parallel resistance with ILIT under certain assumptions. At last, an assumption used for the determination of shunt resistances with ILIT is checked.

Verification of power loss mechanisms contributing to the illuminated lock-in thermography (ilit) signal

The characterization of silicon as-cut wafers is important for process control in solar cell production, since it can serve as starting material quality inspection and give information about a change of material properties caused by different process steps. In particular, spatially resolved characterization tools such as Photoluminescence Imaging (PLI) are useful as an information source. Due to the low signal in a luminescence image of an as-cut wafer a major problem is superimposed laser reflection light if the detection occurs from the illuminated side of the wafer. We present a method which eliminates the spurious reflection contribution by a special image correction technique. The image correction is based on a separate measurement of a reflection topography of the as-cut wafer surface. Additionally we show that for non calibrated luminescence images of as-cut material the bulk lifetime in low quality areas can be estimated by relating PL-intensity in these areas to a saturated PL-intensity value that can be assigned to high quality areas via a simulated curve of relative PL-intensity over minority carrier bulk lifetime. Copyright # 2008 John Wiley & Sons, Ltd.

Spatially Resolved Characterisation of Silicon As-cut Wafers with Photoluminescence Imaging

In order to enhance the passivation quality of thin Al 2 O 3 layers an appropriate pre-deposition cleaning is expected to play an important role In this study we present findings on the influence of the pre-deposition cleaning, post-deposition treatment and surface roughness on the passivation quality of thin ALD Al 2 O 3 layers in an Al 2 O 3 /SiN x stack Especially for 05 nm layers of Al 2 O 3 we found that there is a distinct influence of the cleaning on the passivation quality With RCA cleaning surface recombination values below 10 cm/s on p-type 1 Ω cm Si could be reached for Al 2 O 3 layers of 5 nm as well as of 05 nm thickness Also the influence of surface roughness was examined With smoothed wafers we found an influence of the surface morphology on all process parameters especially the post-deposition treatment Additionally a slight trend towards decreasing surface recombination velocity with decreasing nano-roughness could be seen

Wilhelm Warta

Papers

Photoconductance-Based Excess Carrier Lifetime Measurements on Unpassivated Silicon Samples

Precise Measurement of Solar Cell Performance in Production

Verification of power loss mechanisms contributing to the illuminated lock-in thermography (ilit) signal

Spatially Resolved Characterisation of Silicon As-cut Wafers with Photoluminescence Imaging

Impact of wet-chemical cleaning on the passivation quality of Al 2 O 3 layers