The introduction of a KF post-deposition treatment (KF PDT) of Cu(In,Ga)Se 2 (CIGS) thin films has led to the achievement of several consecutive new world record efficiencies up to 21.7% for the CIGS solar cell technology. The beneficial effect of the KF PDT on the photovoltaic parameters was observed by several groups in spite of differing growth methods of the CIGS layer. For CIGS evaporated at lower temperature on alkali-free, flexible plastic substrates, a postdeposition treatment to add Na was already successfully applied. However with the introduction of additional KF under comparable conditions, distinctly different influences on the final absorber alkali content as well as surface properties are observed. In this work we discuss in more details the intrinsically different role of both alkali-treatments by combining several microstructural and compositional analysis methods. The ion exchange of Na by K in the bulk of the absorber is carefully analyzed, and further evidences for the formation of a K-containing layer on the CIGS surface with increased surface reactivity are given. These results shall serve as a basis for the further understanding of the effects of alkali PDT on CIGS and help identifying research needs to achieve even higher efficiencies.

This review summarizes the current status of Cu(In,Ga)(S,Se) 2 (CIGS) thin film solar cell technology with a focus on recent advancements and emerging concepts intended for higher efficiency and novel applications. The recent developments and trends of research in laboratories and industrial achievements communicated within the last years are reviewed, and the major developments linked to alkali post deposition treatment and composition grading in CIGS, surface passivation, buffer, and transparent contact layers are emphasized. Encouraging results have been achieved for CIGS-based tandem solar cells and for improvement in low light device performance. Challenges of technology transfer of lab's record high efficiency cells to average industrial production are obvious from the reported efficiency values. One section is dedicated to development and opportunities offered by flexible and lightweight CIGS modules.

Recent years have shown the importance of tunable semiconductor lasers in optical sensing. We describe the status quo concerning DFB laser diodes between 760 nm and 3,000 nm as well as new developments aiming for up to 80 nm tuning range in this spectral region. Furthermore we report on QCL between 3 μm and 16 μm and present new developments. An overview of the most interesting applications using such devices is given at the end of this paper.

Solution processing of inorganic thin fi lms has become an important thrust in material research community because it offers low-cost and high-throughput deposition of various functional coatings and devices. Especially inorganic thin fi lm solar cells -macroelectronic devices that rely on consecutive deposition of layers on large-area rigid and fl exible substrates -could benefi t from solution approaches in order to realize their low-cost nature. This article critically reviews existing deposition approaches of functional layers for chalcogenide solar cells with an extension to other thin fi lm technologies. Only true solutions of readily available metal salts in appropriate solvents are considered without the need of pre-fabricated nanoparticles. By combining three promising approaches, an air-stable Cu(In,Ga)Se 2 thin fi lm solar cell with effi ciency of 13.8% is demonstrated where all constituent layers (except the metal back contact) are processed from solutions. Notably, water is employed as the solvent in all steps, highlighting the potential for safe manufacturing with high utilization rates. remarkable improvements in conversion effi ciency. [ 1 ] The highest effi ciency of 21.0% has been achieved for two thin fi lm technologies so far: Cu(In,Ga)Se 2 (CIGS) [ 2 ] and CdTe. [ 3 ] Remarkably, both CIGS and CdTe records are exceeding the highest value of 20.4% for the market leading polycrystalline silicon wafer technology. Kesterite Cu 2 ZnSn(S,Se) 4 (CZTSSe) solar cells are often considered as low-cost alternatives to CIGS and CdTe because they consist of only earth-abundant and nontoxic elements although the effi ciency is currently limited to 12.6% (12.7% not certifi ed). [ 4 ] Well-established dye-sensitized solar cell (DSSC) and amorphous silicon (a-Si) technology peak at 12.3% and 13.4%, respectively. [ 1 ] The most recent boom in TFPV -organometallic halide perovskite cells -has shown an incredible spurt by advancing effi ciency from below 5% to 17.9%(!) within just 3 years. [ 5 ] On the border to classical TFSC is the thin crystalline silicon technology that employs liftoff of 50-micrometer-thick Si wafers to yield up to 21.2%-efficient solar cells. [ 6 ] These massive research and development efforts in the fi eld of TFSC clearly refl ect their commercial value for manufacturing inexpensive effi cient solar modules -rigid or fl exible. Functional layers for the high effi ciency devices are deposited mostly in a batch-to-batch manner using vacuum-based methods such as evaporation, sputtering, or chemical vapor deposition. For example, Figure 1 exhibits a cross-section of a >20% effi cient CIGS solar cell in the so-called substrate confi guration, where 5 out of 6 functional layers are deposited by evaporation or sputtering. In this respect, non-vacuum deposition methods are often promoted as alternative approaches to reduce capital investment costs, offer fast roll-to-roll (R2R) processing and eventually reduce the PV module prices. Particularly desirable among non-vacuum approaches are solutionb...