Temperature Coefficients of Perovskite Photovoltaics for Energy Yield Calculations.

Temperature coefficients for maximum power (T PCE), open circuit voltage (V OC), and short circuit current (J SC) are standard specifications included in data sheets for any commercially available photovoltaic module. To date, there has been little work on determining the T PCE for perovskite photovoltaics (PV). We fabricate perovskite solar cells with a T PCE of -0.08 rel %/°C and then disentangle the temperature-dependent effects of the perovskite absorber, contact layers, and interfaces by comparing different device architectures and using drift-diffusion modeling. A main factor contributing to the small T PCE of perovskites is their low intrinsic carrier concentrations with respect to Si and GaAs, which can be explained by its wider band gap. We demonstrate that the unique increase in E g with increasing temperatures seen for perovskites results in a reduction in J SC but positively influences V OC. The current limiting factors for the T PCE in perovskite PV are identified to originate from interfacial effects.

Triple-halide wide-band gap perovskites with suppressed phase segregation for efficient tandems.

Wide-band gap metal halide perovskites are promising semiconductors to pair with silicon in tandem solar cells to pursue the goal of achieving power conversion efficiency (PCE) greater than 30% at low cost. However, wide-band gap perovskite solar cells have been fundamentally limited by photoinduced phase segregation and low open-circuit voltage. We report efficient 1.67-electron volt wide-band gap perovskite top cells using triple-halide alloys (chlorine, bromine, iodine) to tailor the band gap and stabilize the semiconductor under illumination. We show a factor of 2 increase in photocarrier lifetime and charge-carrier mobility that resulted from enhancing the solubility of chlorine by replacing some of the iodine with bromine to shrink the lattice parameter. We observed a suppression of light-induced phase segregation in films even at 100-sun illumination intensity and less than 4% degradation in semitransparent top cells after 1000 hours of maximum power point (MPP) operation at 60°C. By integrating these top cells with silicon bottom cells, we achieved a PCE of 27% in two-terminal monolithic tandems with an area of 1 square centimeter.

Understanding Degradation Mechanisms and Improving Stability of Perovskite Photovoltaics.

This review article examines the current state of understanding in how metal halide perovskite solar cells can degrade when exposed to moisture, oxygen, heat, light, mechanical stress, and reverse bias. It also highlights strategies for improving stability, such as tuning the composition of the perovskite, introducing hydrophobic coatings, replacing metal electrodes with carbon or transparent conducting oxides, and packaging. The article concludes with recommendations on how accelerated testing should be performed to rapidly develop solar cells that are both extraordinarily efficient and stable.