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Williams, Spencer T.

Publications and source records attributed to Williams, Spencer T..

6 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Improved efficiency and stability of Pb–Sn binary perovskite solar cells by Cs substitution

Partially replacing Pb with Sn in organic–inorganic lead halide perovskites has been proven as a promising approach to reduce environmental toxicity and develop low bandgap (as low as 1.20 eV) perovskite solar cells (PVSCs) beneficial for constructing perovskite-based tandem solar cells. In this work, we demonstrated that partially replacing MA + or FA + with Cs + in a Pb–Sn binary perovskite system can effectively retard the associated crystallization rate to facilitate homogenous film formation, subsequently resulting in enhanced device performance and stability, especially for high Sn-containing compositions. Here, the representative MA 0.9 Cs 0.1 Pb 0.5 Sn 0.5 I 3 PVSC with a low Eg of 1.28 eV not only achieves an improved efficiency up to 10.07% but also possesses much improved thermal and ambient stability as compared to the pristine MAPb0.5Sn0.5I3 PVSC showing poorer efficiency (6.36%) and stability. Similarly, when Cs was introduced into FAPb 1-x Sn x I 3 perovskite, enhanced performance was observed, affirming its general applicability and beneficial role in mediating the crystal growth and film formation of Pb–Sn binary perovskites.

14 SOLAR ENERGY↗
DOE OSTI2016

Design rules for the broad application of fast (<1 s) methylamine vapor based, hybrid perovskite post deposition treatments

While organo-metal halide perovskite photovoltaics have seen rapid development, growth of high quality material remains a challenge. Herein, we report a facile post deposition treatment utilizing coordination between methylamine (CH 3 NH 2 ) vapor and CH 3 NH 3 PbI 3 perovskite that rapidly improves film quality, enhancing power conversion efficiency (PCE) by ~9%. We further comprehensively analyze the physical impact of this process with regard to the material's optoelectronic properties and its detailed microstructural changes. Connecting this with an analysis of the source of organo-metal halide perovskite reactivity toward the vapor as well as phase behavior as a function of CH 3 NH 2 vapor pressure and time, we provide design rules for the broad, rational extension of this process to new systems and scales.

14 SOLAR ENERGY↗
DOE OSTI2016

Abnormal Current–Voltage Hysteresis Induced by Reverse Bias in Organic–Inorganic Hybrid Perovskite Photovoltaics

In this study, reverse bias (RB)-induced abnormal hysteresis is investigated in perovskite solar cells (PVSCs) with nickel oxide (NiOx)/methylammonium lead iodide (CH 3 NH 3 PbI 3 ) interfaces. Through comprehensive current-voltage (I-V) characterization and bias-dependent external quantum efficiency (EQE) measurements, we demonstrate that this phenomenon is caused by the interfacial ion accumulation intrinsic to CH 3 NH 3 PbI 3 . Subsequently, via systematic analysis we discover that the abnormal I-V behavior is remarkably similar to tunnel diode I-V characteristics and is due to the formation of a transient tunnel junction at NiO x /CH 3 NH 3 PbI 3 interfaces under RB. The detailed analysis navigating the complexities of I-V behavior in CH 3 NH 3 PbI 3 -based solar cells provided here ultimately illuminates possibilities in modulating ion motion and hysteresis via interfacial engineering in PVSCs. Moreover, this work shows that RB can alter how CH 3 NH 3 PbI 3 contributes to the functional nature of devices and provides the first steps toward approaching functional perovskite interfaces in new ways for metrology and analysis of complex transient processes.

14 SOLAR ENERGY↗
DOE OSTI2016

Current Challenges and Prospective Research for Upscaling Hybrid Perovskite Photovoltaics

Organic-inorganic hybrid perovskite photovoltaics (PSCs) are poised to push toward technology translation, but significant challenges complicating commercialization remain. Though J-V hysteresis and ecotoxicity are uniquely imposing issues at scale, CH 3 NH 3 PbI 3 degradation is by far the sharpest limitation to the technology’s potential market contribution. Herein, we offer a perspective on the practical market potential of PSCs, the nature of fundamental PSC challenges at scale, and an outline of prospective solutions for achieving module scale PSC production tailored to intrinsic advantages of CH 3 NH 3 PbI 3 . Although integrating PSCs into the energy grid is complicated by CH 3 NH 3 PbI 3 degradation, the ability of PSCs to contribute to consumer electronics and other niche markets like those organic photovoltaics have sought footing in rests primarily upon the technology’s price point. Thus, slot die, roll-to-roll processing has the greatest potential to enable PSC scale-up, and herein, we present a perspective on the research necessary to realize fully printable PSCs at scale.

14 SOLAR ENERGY↗
DOE OSTI2015

Room-temperature, solution-processable organic electron extraction layer for high-performance planar heterojunction perovskite solar cells

Here in this work, we describe a room-temperature, solution-processable organic electron extraction layer (EEL) for high-performance planar heterojunction perovskite solar cells (PHJ PVSCs). This EEL is composed of a bilayered fulleropyrrolidinium iodide (FPI)-polyethyleneimine (PEIE) and PC 61 BM, which yields a promising power conversion efficiency (PCE) of 15.7% with insignificant hysteresis. We reveal that PC 61 BM can serve as a surface modifier of FPI-PEIE to simultaneously facilitate the crystallization of perovskite and the charge extraction at FPI-PEIE/CH 3 NH 3 PbI 3 interface. Furthermore, the FPI-PEIE can also tune the work function of ITO and dope PC 61 BM to promote the efficient electron transport between ITO and PC 61 BM. Based on the advantages of room-temperature processability and decent electrical property of FPI-PEIE/PC 61 BM EEL, a high-performance flexible PVSC with a PCE ~10% is eventually demonstrated. Lastly, this study shows the potential of low-temperature processed organic EEL to replace transition metal oxide-based interlayers for highly printing compatible PVSCs with high-performance.

14 SOLAR ENERGY↗