Perceiving the temperature coefficients of carbon-based perovskite solar cells

Abstract

Perovskite solar cells (PSCs) have emerged in a “catfish effect” of other established photovoltaic technologies with the rapid development of high-power conversion efficiency (PCE) and low-cost fabrication. Among various kinds of PSCs, organic hole transport layer (HTL)-free carbon-based PSCs (c-PSCs) have been considered as the most promising devices due to their excellent stability. However, temperature becomes one of the crucial factors in determining the pace of PSC commercialization. Temperature stress at the interface between the perovskite film and the charge transport layer is an essential factor in determining the performance of c-PSCs. This work assesses the correlation between the temperature coefficient (T_C) and different photovoltaic parameters for HTL-free c-PSCs. To evaluate different photovoltaic parameters of the c-PSC as a function of temperature, two different testing approaches namely under steady temperature (S_T) and transient temperature (T_T) conditions have been considered across a wide temperature window (5–75 °C) under 1 Sun 1.5 AM. Here T_T testing involves subjecting a single c-PSC to a continuous temperature treatment, whereas S_T testing consists of specific temperature treatment of an individual c-PSC. The maximum efficiency achieved at 25 °C for T_T testing devices is ∼14.5%, which is ∼11% higher than that of S_T testing devices (PCE ∼ 13%). Moreover, the efficiency temperature coefficient (ETC) for S_T testing was found to be 3.5 × 10⁻² (5 °C ≤ T ≤ 25 °C) and −2.1 × 10⁻² (25 °C ≤ T ≤ 75 °C), whereas the ETC values of T_T testing devices were +2.5 × 10⁻² (5 °C ≤ T ≤ 25 °C) and −1.8 × 10⁻² (25 °C ≤ T ≤ 75 °C), respectively. The outcome of temperature stress transmitting through different interfacial layers was further investigated by thermal imaging of T_T devices. On the other hand, X-ray diffraction and scanning electron microscopy structural analyses were performed to understand the effect of thermal stress on the overall performance of S_T devices. It has been observed that T_C values obtained under T_T testing conditions are reversible, whereas in the case of S_T testing the T_C values are irreversible which shows degradation of the device.