Post-deposition annealing and interfacial atomic layer deposition buffer layers of Sb2Se3/CdS stacks for reduced interface recombination and increased open-circuit voltages

in Progress in Photovoltaics (2022)

How band tail recombination influences the open-circuit voltage of solar cells.

in Progress in Photovoltaics (2021)

Absorber composition: A critical parameter for the effectiveness of heat treatments in chalcopyrite solar cells

in Progress in Photovoltaics (2020)

Post-device heat treatment (HT) in chalcopyrite [Cu(In,Ga)(S,Se)2] solar cells is known to improve the performance of the devices. However, this HT is only beneficial for devices made with absorbers grown ... [more ▼]

Post-device heat treatment (HT) in chalcopyrite [Cu(In,Ga)(S,Se)2] solar cells is known to improve the performance of the devices. However, this HT is only beneficial for devices made with absorbers grown under Cu-poor conditions but not under Cu excess.. We present a systematic study to understand the effects of HT on CuInSe2 and CuInS2 solar cells. The study is performed for CuInSe2 solar cells grown under Cu-rich and Cu-poor chemical potential prepared with both CdS and Zn(O,S) buffer layers. In addition, we also study Cu-rich CuInS2 solar cells prepared with the suitable Zn(O,S) buffer layer. For Cu-poor selenide device low-temperature HT leads to passivation of bulk, whereas in Cu-rich devices no such passivation was observed. The Cu-rich devices are hampered by a large shunt. The HT decreases shunt resistance in Cu-rich selenides, whereas it increases shunt resistance in Cu-rich sulfides.. The origin of these changes in device performance was investigated with capacitance-voltage measurement which shows the considerable decrease in carrier concentration with HT in Cu-poor CuInSe2, and temperature dependent current-voltage measurements show the presence of barrier for minority carriers. Together with numerical simulations, these findings support a highly-doped interfacial p+ layer device model in Cu-rich selenide absorbers and explain the discrepancy between Cu-poor and Curich device performance. Our findings provide insights into how the same treatment can have a completely different effect on the device depending on the composition of the absorber. [less ▲]

High‐performance low bandgap thin film solar cells for tandem applications

in Progress in Photovoltaics (2018)

Thin film tandem solar cells provide a promising approach to achieve high efficiencies. These tandem cells require at least a bottom low bandgap and an upper high bandgap solar cell. In this contribution ... [more ▼]

Thin film tandem solar cells provide a promising approach to achieve high efficiencies. These tandem cells require at least a bottom low bandgap and an upper high bandgap solar cell. In this contribution, 2 high‐performance Cu(In,Ga)Se2 cells with bandgaps as low as 1.04 and 1.07 eV are presented. These cells have shown certified efficiencies of 15.7% and 16.6% respectively. Measuring these cells under a 780‐nm longpass filter, corresponding to the bandgap of a typical top cell in tandem applications (1.57 eV), they achieved efficiencies of 7.9% and 8.3%. Admittance measurements showed no recombination active deep defects. One additional high‐performance CuInSe2 thin film solar cell with bandgap of 0.95 eV and efficiency of 14.1% is presented. All 3 cells have the potential to be integrated as bottom low bandgap cells in thin film tandem applications achieving efficiencies around 24% stacked with an efficient high bandgap top cell. [less ▲]

Visualizing the performance loss of solar cells by IR thermography — an evaluation study on CIGS with artificially induced defects

in Progress in Photovoltaics (2016), 24(7), 1001-1008

Local electric defects may result in considerable performance losses in solar cells. Infrared (IR) thermography is one im- portant tool to detect these defects on photovoltaic modules. Qualitative ... [more ▼]

Local electric defects may result in considerable performance losses in solar cells. Infrared (IR) thermography is one im- portant tool to detect these defects on photovoltaic modules. Qualitative interpretation of IR images has been carried out successfully, but quantitative interpretation has been hampered by the lack of “calibration” defects. The aims of this study are to (i) establish methods to induce well-defined electric defects in thin-film solar cells serving as “calibration” defects and to (ii) assess the accuracy of IR imaging methods by using these artificially induced defects. This approach paves the way for improving quality control methods based on imaging in photovoltaic. We created ohmic defects (“shunts”) by using a focused ion beam and weak diodes (“interface shunts”) by applying a femto-second laser at rather low power on copper indium gallium selenide cells. The defects can be induced precisely and reproducibly, and the severity of the defects on the electrical performance can be well adjusted by focused ion beam/laser parameters. The successive assess- ment of the IR measurement (ILIT-Voc) revealed that this method can predict the losses in Pmpp (maximal power extract- able) with a mean error of below 10%. [less ▲]

Highly conductive ZnO films with high near infrared transparency

in Progress in Photovoltaics (2015)

We present an approach for deposition of highly conductive nominally undoped ZnO films that are suitable for the n-type window of low band gap solar cells. We demonstrate that low-voltage radio frequency ... [more ▼]

We present an approach for deposition of highly conductive nominally undoped ZnO films that are suitable for the n-type window of low band gap solar cells. We demonstrate that low-voltage radio frequency (RF) biasing of growing ZnO films during their deposition by non-reactive sputtering makes them as conductive as when doped by aluminium (ρ≤1·10−3Ω cm). The films prepared with additional RF biasing possess lower free-carrier concentration and higher free-carrier mobility than Al-doped ZnO (AZO) films of the same resistivity, which results in a substantially higher transparency in the near infrared region (NIR). Furthermore, these films exhibit good ambient stability and lower high-temperature stability than the AZO films of the same thickness. We also present the characteristics of Cu(InGa)Se2, CuInSe2 and Cu2ZnSnSe4-based solar cells prepared with the transparent window bilayer formed of the isolating and conductive ZnO films and compare them to their counterparts with a standard ZnO/AZO bilayer. We show that the solar cells with nominally undoped ZnO as their transparent conductive oxide layer exhibit an improved quantum efficiency for λ > 900 nm, which leads to a higher short circuit current density JSC. This aspect is specifically beneficial in preparation of the Cu2ZnSnSe4 solar cells with band gap down to 0.85 eV; our champion device reached a JSC of nearly 39 mAcm−2, an open circuit voltage of 378 mV, and a power conversion efficiency of 8.4 %. [less ▲]

Solution-based processing of Cu(In,Ga)Se2 absorber layers for 11% efficiency solar cells via a metallic intermediate

in Progress in Photovoltaics (2014)

In this work, a low cost solution-based method for the deposition of uniform Cu-In-Ga layers compatible with roll-to-roll processing is described. As ink system we use metal carboxylates dissolved in a ... [more ▼]

In this work, a low cost solution-based method for the deposition of uniform Cu-In-Ga layers compatible with roll-to-roll processing is described. As ink system we use metal carboxylates dissolved in a mixture of a nitrogen containing base and an alcohol. This solution can be coated homogeneously under inert atmosphere using a doctor blade technique. With this method and appropriate precursor concentrations, crack-free metal layers with dry-film thicknesses of more than 700 nm can be deposited in one fast step. For the controlled film formation during the drying of the solvents a flow channel has been used to improve the evaporative mass transport and the convective gas flows of any unwanted organic species. Due to the absence of organic binders with high molecular weight, this step allows the formation of virtually pure metal layers. Elementary analyses of the dried thin films reveal less than 5 wt% of carbon residues at 200°C. In situ X-ray diffraction data of the drying step show the formation of Cu-In-Ga alloys. The subsequent processing of Cu(In,Ga)Se2 chalcopyrites with evaporated elemental selenium takes place in a separate tube oven under inert atmosphere. Photoelectric measurements of cells with CdS buffer and ZnO window layer reveal a short-circuit current of 29 mA/cm2, an open-circuit voltage of 533 mV, and a fill factor of 0.69 under standard conditions. Thus efficiencies of up to 11% on 0.5 cm2 area without antireflective coating have been achieved. [less ▲]

Kesterites - a challenging material for solar cells.

in Progress in Photovoltaics (2012), 20

Cu2ZnSnSe4 thin film solar cells produced by selenisation of magnetron sputtered precursors

in Progress in Photovoltaics (2009), 17(5), 315-319