Search

37th European Photovoltaic Solar Energy Conference and Exhibition; 596-600, In this paper, the complete formation of various perovskite thin films during spin-coating and subsequent annealing is monitored in-situ by high-speed optical reflectance spectroscopy. Furthermore, first results for anti-solvent drip processes and the deposition of perovskite semiconductors on top of CIGS-based samples for tandem applications are presented. It is shown, that a complete “fingerprint” of the film formation process can be obtained and crucial properties like the absorption edge and its evolution during film formation can be deduced. The method also allows for real-time measurements of the amount of the remaining precursor wet-film. All this information is well-suited for tailoring film properties and identifying new paths for the optimization of performance or yield. Hence, this technology can enable and accelerate process development for perovskite thin films. This paper focuses on the experimental implementation of the in-situ measurements and presents first results on absorption edge evolution monitoring, spincoating kinetics and annealing phase transformations.

The metal ion chelating property was conferred onto silicon (Si) and gold (Au) surfaces by direct electrografting of the 4-[(carboxymethyl)thio]benzenediazonium cation (4-CMTBD). Infrared spectroscopic ellipsometry showed the presence of characteristic phenyl and carbonyl vibrational bands on the functionalized surfaces as a proof of existence of surface-bound organic units of 4-carboxymethl)thio]benzene, (4-CMTB). The loss of diazonium group (N N+) upon electrografting of 4-CMTBD was investigated using IR spectroscopy. A Faradaic efficiency of about 18.8-20.0% was realized in mass deposition experiments for grafting 4-CMTB on the Au surface using an electrochemical quartz crystal microbalance technique. Raman spectroscopy performed on the Si-(4-CMTB) surface after treatment with topper (Cu) ion solution provided evidence of metal ion chelation based on an observed v(Cu-O) peak at about 487 cm(-1) and a v(Ou-S) signal at about 267 cm(-1). The binding of Cu ions by the chelating ligands also caused a red shift of about 10 cm(-1) in the Raman spectrum of the Si-(4-CMTB)-Cu surface within the spectral region, characteristic of the v(C-O) signal. X-ray photoelectron spectroscopy investigations showed indications of the Cu(II) ion species chelated by the surface-bound carboxymethylthio ligands. The functionalized surface, Si-(4-CMTB), constitutes an alternative metal ion chelating surface that may potentially be developed for applications in trace-level trapping of Cu ions.

Electrografting of gold and graphene surfaces by functional p-(N-maleimido)phenyl groups was performed by reduction of p-(N-maleimido)phenyldiazonium tetrafluoroborate. The reduction was carried out using cyclic voltammetry coupled with micro-gravimetric measurements by means of electrochemical quartz crystal microbalance (EQCM). The overall deposited mass on gold was higher than on graphene. However, the Faradaic efficiency was lower on Au (14%) compared to graphene (22%) after the first potential scan. Subsequently, the maleimide functional groups have been tested for immobilization of terminal thiols using (4-nitrobenzyl)mercaptan for the functionalized graphene surface and a cysteine-modified peptide for the functionalized gold surface. The functionalization by p-(N-maleimido)phenyl groups and the following thiol coupling of the particular surface was proven by infrared spectroscopic ellipsometry (IRSE). In addition, the interaction of the tetrabutylammonium and tetrafluoroborate ions present in the electrolyte with the Au and graphene electrodes was investigated by EQCM and revealed less electrostatic interaction of graphene with these ions in solution compared to the metal (Au) surface.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 1104-1107, The diffusion or transport length (L) of photo-generated charge carriers has been measured directly in CH3NH3PbI3 powders by applying the surface photovoltage (SPV) method after Goodman. The average size of crystallites in the powder was changed between tens of μm and about 1 mm. The values of L ranged between 3 and 30 μm and decreased to 0.6 μm in some cases after light soaking. It was shown that light soaking does not necessarily lead to a degradation of L. An instability of L was observed under certain conditions depending on conditioning of CH3NH3PbI3 crystallites, the value of the constant SPV signal and light soaking. The results have consequences for the further development of solar cells based on CH3NH3PbI3.

Tandem solar cells consisting of perovskite and silicon absorbers have the potential to outperform respective state of the art single junction efficiencies. However, their development requires the gentle deposition of a transparent electrode onto the hybrid perovskite and its organic layers. Implementation of large area graphene obtained by chemical vapor deposition seems to be an excellent solution. In this paper, we present the impact of graphene on perovskite solar cells and their organic layers. Direct application of graphene on CH3NH3PbI3 is limited by a highly defective interface but insertion of spiro OMeTAD enables a defect free implementation. Solar cells containing transparent graphene contacts approach identical electrical performance compared to devices with standard Au contacts. Hall effect measurements of graphene on various organic thin films, revealed the importance of field effect doping. Gained knowledge enabled the development of a strategy to increase the charge carrier density in graphene by 60 , while lowering graphene sheet resistance by 24 . This combined route of spiro OMeTAD and stabilized adsorbent doping is an important step toward the targeted application in high performance monolithic perovskite silicon tandem solar cells