The performance of the electron transport layer (ETL) plays a critical role in extending the operational lifespan of organic photovoltaic devices. ZnO is an excellent electron transport layer used in the printable organic photovoltaic cells. A comparison of Ca and ZnO as the ETL in encapsulated bulk heterojunction OPV devices has been undertaken with the device stability dependence on light soaking, temperature, irradiance, and thermal cycling recorded. It was observed that the OPV devices using Ca ETL decayed faster than the ZnO ETL devices under the same light illumination. The degradation in a Ca ETL device is ascribed to the formation of an insulating calcium oxide layer at the ETL interfaces. Photoluminescence (PL) spectroscopy revealed a higher PL signal for the degraded Ca ETL devices compared to the ZnO ETL devices. Power conversion efficiency (PCE) of the ZnO ETL devices was found to be much more stable than the Ca devices. The PCE for ZnO ETL devices still retained 40% of their initial value while the Ca ETL devices failed completely over the period of 18 days in the study, leading to a clear outcome of the study.

The optical design, fabrication, and evaluation of a low-cost solar simulator for photovoltaic device testing are presented in this article. Ten different high-power light-emitting diodes (LEDs) in the range 350–1100 nm are arrayed in a hexagonal geometry, enabling excellent spatial nonuniformity of irradiance (< 2%) while minimizing the number of LEDs required for solar emission spectral match. The solar simulator design demonstrates Class AAA performance at 100 mW / cm ² output irradiance over 70 cm ² with < 0.05% temporal instability of irradiance. The low total material cost of the solar simulator (< $700 USD) ensures an economic LED-based Class AAA solar simulator for electrical performance testing of photovoltaic devices.

The solar simulator has allowed all photovoltaic devices to be developed and tested under laboratory conditions. Filtered xenon arc lamps were the gold-standard source for solar simulation of small-area silicon photovoltaic devices; however, scaling these devices to illuminate large areas is neither efficient nor practical. Large-area solar simulation to meet appropriate spectral content and spatial nonuniformity of irradiance (SNI) standards has traditionally been difficult and expensive to achieve, partly due to the light sources employed. LED-based solar simulation allows a better electrical efficiency and uniformity of irradiance while meeting spectral intensity requirements with better form factors. This work details the design based on optical modeling of a scalable, large-area, LED-based, solar simulator meeting Class AAA performance standards formed for inline testing of printed solar cells. The modular design approach employed enables the illuminated area to be expanded in quanta of ~260 cm² to any preferred illumination area. A 640 cm² area illuminated by two adjacent PCB units has a measured total emission of 100 mW/cm², with a SNI of 1.7% and an excellent approximation to the AM1.5G spectrum over the wavelength range of 350–1100 nm. The measured long-term temporal instability of irradiance (TIE) is <0.5% for a 550-min continuous run. This work identifies the design steps and details the development and measurement of a scalable large-area LED-based solar simulator of interest to the PV testing community, and others using solar simulators.