Temperature dependent transient surface photovoltage spectroscopy of a Cu1.95Zn1.1Sn0.96Se4 kesterite single phase powder

An off-stoichiometric but single phase Cu1.95Zn1.1Sn0.96Se4 kesterite powder was investigated by temperature dependent transient surface photovoltage (SPV) spectroscopy. SPV signals excited at different wavelengths were transformed into SPV spectra that depended on the response time of measurement. Shallow electronic states and states with transition energies at 0.83 eV or 0.78… 0.9 eV were distinguished. The temperature dependence of the band gap of Cu1.95Zn1.1Sn0.96Se4 was obtained. Results were discussed on the basis of defects in Cu-poor and Zn-rich kesterite

Photoinduced charge dissociation and transport at P3HT ITO interfaces studied by modulated surface spec troscopy

Results of a temperature dependence study of photoinduced charge separation across P3HT nanocrystals at P3HT ITO interfaces have been investigated by modulated surface photovoltage SPV spectroscopy in a fixed capacitor arrangement. The SPV measurements were correlated with the crystalline sizes of P3HT nanocrystals determined by grazing incidence X ray diffraction GIXRD . The crystalline sizes of P3HT nanocrystals were varied systematically by progressive heating cooling cycles identical for SPV and GIXRD measurements. Photovoltage signals, indication of photoinduced charge dissociation in space, at the P3HT ITO interface were collected, and electrons were separated across the first monolayer of P3HT nanocrystals at the P3HT ITO interface due to band bending. The activation energies for quenching of the inphase and phase shifted by 90 SPV signals were 0.7 and 0.6 eV, respectively. Thermal activation of the formation of P3HT nanocrystals was of the same order as the enthalpy of fusion of ideal crystals from regioregular P3HT. A schematic drawing of photoinduced charge separation at the P3HT ITO is propose

An analytical approach to CH3NH3PbI3 perovskite solar cells based on different hole transport materials

Organic halide perovskite solar cells PSC s have achieved high efficiencies in a relatively short amount of time. In order to attain efficiency in the neighborhood of the Shockley Queisser SQ limit, additional modifications are continuously being made. A simple lumped circuit model, which had been previously used to investigate organic and inorganic thin film solar cells, is used in this study to gain more insight into the effects of these modifications on the performance related factors. It is examined that the changes in the lumped circuit parameters associated with the deviceperformances when different hole transpor t mater ials HTM s such as PEDOT PSS, NiOx,and PTAA or when different underneath substrates areemployed. The reason for this interest is the well accepted fact that the defect formation greatly hinders the formation of photo generated charge carriers. Using the time resolved surface photovoltage measurements, we show that the photo induced charge sep ration and charge migration are greatly influenced by the HTM s. The resulting changes were analyzed in detail. Unlike what occurs when CH3NH3PbI3 is deposited onto bare ITO or PEDOT PSS, the long lived from micro millisecond charge separations are observed when the NiOx is used as the HTL. These observations point to the need to examine other low cost HLM s or combinations of them for use to improve the solar energy conversion efficiencies of the PSC

Understanding the Interplay of Transport-Morphology-Performance in PBDB-T-Based Polymer Solar Cells

Polymer–polymer blends have been reported to exhibit exceptional thermal and ambient stability. However, power conversion efficiencies (PCEs) from devices using polymeric acceptors have been recorded to be significantly lower than those based on conjugated molecular acceptors. Herein, two organic nonfullerene bulk heterojunction (BHJ) blends ITIC:PBDB-T and N2200:PBDB-T, together with their fullerene counterpart, PCBM:PBDB-T, are adopted to understand the effect of electron acceptors on device performance. Free charge carrier properties using time-resolved microwave conductivity (TRMC) measurements are comprehensively investigated. The nonfullerene devices show an improved PCE of 10.06% and 6.65% in the ITIC- and N2200-based cells, respectively. In comparison, the PCBM:PBDB-T-based devices yield a PCE of 5.88%. The optimal N2200:PBDB-T produced the highest TRMC mobility, longest lifetime, and greatest free-carrier diffusion length. It is found that such phenomena can be associated with the unfavorable morphology of the all-polymer BHJ microstructure. In contrast, the solar cells using either the PCBM or ITIC acceptors display a more balanced donor and acceptor phase separation, leading to more efficient free-carrier separation and transport in the operating device. By sacrificing efficiency for superior stability, it is shown that the improved structure in all-polymer blend can deliver a more stable morphology under thermal stress