Showing papers by "Stefan W. Glunz published in 2016"

UV Degradation and Recovery of Perovskite Solar Cells

Abstract: Although the power conversion efficiency of perovskite solar cells has increased from 3.81% to 22.1% in just 7 years, they still suffer from stability issues, as they degrade upon exposure to moisture, UV light, heat, and bias voltage. We herein examined the degradation of perovskite solar cells in the presence of UV light alone. The cells were exposed to 365 nm UV light for over 1,000 h under inert gas at <0.5 ppm humidity without encapsulation. 1-sun illumination after UV degradation resulted in recovery of the fill factor and power conversion efficiency. Furthermore, during exposure to consecutive UV light, the diminished short circuit current density (Jsc) and EQE continuously restored. 1-sun light soaking induced recovery is considered to be caused by resolving of stacked charges and defect state neutralization. The Jsc and EQE bounce-back phenomenon is attributed to the beneficial effects of PbI2 which is generated by the decomposition of perovskite material.

Impact of the firing temperature profile on light induced degradation of multicrystalline silicon

Abstract: Light- and elevated temperature-induced degradation in multicrystalline silicon can reduce the efficiency of solar cells significantly In this work, the influence of the firing process and its temperature profile on the degradation behaviour of neighbouring mc-Si wafers is analysed Five profiles with measured high peak temperatures ≥800 °C and varying heating and cooling ramps are examined With spatially resolved and lifetime calibrated photoluminescence images, normalized defect concentrations N*t are calculated to determine the degradation intensity Wafers that underwent a fast firing process typical for industrial solar cell production show a significantly stronger degradation than samples that were subjected to the same peak temperature but with slower heating and cooling rates A spatially resolved analysis of the carrier lifetime in the whole wafer shows that the degradation begins in low lifetime areas around dislocation clusters, spreading into good grains after several hours By the use of optimized ramp-up and/or ramp-down rates during the firing even at very high peak temperatures, light and elevated temperature induced degradation can be suppressed (© 2016 WILEY-VCH Verlag GmbH &Co KGaA, Weinheim)

Comprehensive simulation study of industrially relevant silicon solar cell architectures for an optimal material parameter choice

Abstract: Solar cell production always requires a tradeoff between cell efficiency and production costs. This also concerns the choice of the silicon base material. In general, a long base lifetime is beneficial to achieve high conversion efficiency, but it strongly depends on the cell concept to which extent the cell performance is improved and whether a payback of the higher material costs can be expected. Therefore, in this comprehensive simulation study of various industrially relevant solar cell architectures, we present an investigation of the influence of the bulk lifetime and the resistivity of the base material on the cell performance. A consistent set of cell and simulation parameters is chosen to allow for a direct quantitative comparison of the different cell types. The parameters were chosen rather conservatively in order to describe realistic industrial cells and not record laboratory cells. The observed trends are analyzed using detailed loss breakdowns and are compared with experimental results. For various cell concepts, critical lifetimes τcrit can be observed for which the optimal material parameters change with increasing bulk lifetime when comparing materials of different base resistivity. The underlying physical reasons are explained in detail to accomplish two major aims: (i) generating a better understanding of limitations and challenges concerning different solar cell concepts and (ii) serving as a guide for an optimal material parameter choice for different cell architectures. Copyright © 2016 John Wiley & Sons, Ltd.

High work function metal oxides for the hole contact of silicon solar Cells

Abstract: The applicability of molybdenum, tungsten and vanadium oxide as a hole contact for silicon wafer based solar cells is explored. The Si heterojunctions for which these materials are in direct contact with the c-Si absorber, featuring an additional a-Si:H passivation layer or where these materials are used as an additional contact layer in-between the TCO / a-Si:H(p) Schottky contact are addressed. Compared to the standard TCO / a-Si:H(p) / a-Si:H(i) / c-Si heterojunction an efficiency (1 % abs ) and fill factor gain (1.5 % abs ) is obtained if a-Si:H(p) is replaced by molybdenum and if tungsten oxide is applied as an additional contact layer at the TCO / a-Si:H(p) contact. For the simple structure without intrinsic and doped a-Si:H and tungsten or vanadium oxide in direct contact to the c-Si absorber, efficiencies comparable to the reference were obtained.

Theoretical and experimental investigation of aluminum-boron codoping of silicon

Abstract: We present a detailed study on aluminum-boron codoping of silicon by alloying from screen-printed aluminum pastes containing boron additives (Al–B pastes). We derive an analytical model for the formation of the Al–B acceptor profiles by quantitatively describing (i) the composition of the Al–B–Si melt and (ii) the incorporation of Al and B acceptor atoms into the recrystallizing Si lattice. We show that measured Al–B dopant profiles can be excellently described by this model, which therefore offers a straightforward method for the comprehensive investigation of alloying from Al–B pastes. The formation of a characteristic kink in the Al–B dopant profile curve can thus be ascribed to the exhaustion of the B additive dissolution during alloying. By intentionally adding elemental B powder to an Al paste, we demonstrate that only a low percentage of the B powder actually dissolves into the melt. We show that this incomplete dissolution of the B additive strongly affects the recombination characteristics of Al–B–p+ regions and, thus, is an important element of alloying from Al–B pastes. This study therefore provides improved understanding of aluminum-boron codoping of silicon. Copyright © 2015 John Wiley & Sons, Ltd.

Monolithic Perovskite Silicon Tandem Solar Cells with Advanced Optics

Abstract: To realize high efficiency monolithic perovskite silicon tandem solar cells, we develop low-temperature processes for the perovskite top cell, rear-side light trapping, optimized perovskite growth, transparent contacts and recombination interconnection layers, and adapted characterization methods.