Integration of a Solution-Processed Perovskite Solar Cell with a Battery-Peltier Cooling System for Portable Medical Refrigeration
SUMMARY
Access to medical care in remote and off-grid regions remains a global challenge, especially in developing nations and disaster-affected areas. One key problem is the cold chain. Many vaccines and medicines must be kept within a narrow temperature range, which is hard to maintain without reliable electricity. Silicon solar panels are one possible power source, but their manufacturing requires high-vacuum equipment and processing temperatures above 1,000 °C, which makes local production difficult. Here, we test whether a solution-processed perovskite solar cell (PSC), which can be made at room pressure by spin-coating, can power a portable cooling system instead. We hypothesized that a PSC paired with a lithium-ion battery and a 12 W Peltier cooler could maintain the WHO vaccine cold-chain range of 2-8 °C inside an insulated container. We fabricated a PSC and measured an open-circuit voltage of 0.95 V, a short-circuit current of 84 µA, and a fill factor of 48 % under LED illumination. After pre-cooling the chamber to 10 °C, the battery-driven Peltier held the interior at 12-13 °C. Although the prototype did not reach the 2-8 °C target, a larger PSC array, an expanded battery pack, and a two-stage Peltier should bring the system into the cold-chain range.
INTRODUCTION
The COVID-19 pandemic underscored the need for resilient medical infrastructure that reaches every community, not just urban centers. One of the hardest logistical challenges is the cold chain: many vaccines and medicines must be kept within a narrow temperature range during storage and transport [1,2]. The World Health Organization (WHO) recommends that most routine vaccines be kept between 2 °C and 8 °C. In regions without reliable electricity, maintaining this range is very difficult, which limits vaccine access and worsens health inequality. Solutions for these regions need to follow the principles of appropriate technology. Low-cost, decentralized, maintainable by local communities, and adapted to local conditions. Solar power is a strong candidate because sunlight is available almost everywhere.
Crystalline silicon (c-Si) currently makes up roughly 95 % of the global photovoltaic (PV) market [3]. Silicon cells are stable and have reached commercial efficiencies of 20-24 %, with laboratory records approaching the Shockley-Queisser limit of about 29 % [4,5]. These properties make silicon ideal for utility-scale power plants and urban grids. However, producing high-purity silicon wafers requires specialized facilities, high-vacuum equipment, and processing temperatures above 1,000 °C. This level of industrial infrastructure is hard to set up in remote regions, which means silicon panels usually have to be manufactured elsewhere and shipped in. There is therefore an opportunity to complement silicon with alternative photovoltaic technologies whose fabrication is better matched to small-scale, local deployment.
Perovskite solar cells (PSCs) are one such alternative. Perovskites are crystals with the formula ABX₃, where A, B, and X are different ions. In this study, we used a lead-halide perovskite. Unlike silicon, perovskite layers can be deposited from a liquid precursor at room pressure using techniques such as spin-coating, slot-die coating, or inkjet printing [6,7]. These methods avoid high-vacuum, high-temperature equipment, which lowers cost and makes the technology a better fit for resource-constrained settings. Most PSC research, however, has focused on pushing efficiency in small-area lab devices (typically less than 0.1 cm²) using compositional engineering and interface passivation, with reported efficiencies above 25 % [8,9].
In this study, we built and tested a prototype in which a fabricated PSC charges a lithium-ion battery, which then powers a Peltier thermoelectric cooler inside an insulated container. We hypothesized that this integrated system could maintain the WHO vaccine cold-chain range of 2-8 °C. If the PSC array delivered enough current to offset the Peltier's discharge rate, the system would hold the target temperature. By measuring the actual performance of the system, we aimed to test whether the PSC-battery-Peltier architecture is a viable basis for a portable cold-chain device, and to identify the specific component-level scaling needed to reach the target range.
Student Authors
Daniel Chung, KIS (High School)
Co-authors
Seokho Kim, University of Virginia, VA
Hui Joon Park, Hanyang University, Seoul, RoK
RESULT
The prototype provides decentralized refrigeration by harvesting solar energy with a perovskite solar cell. The system has three modules, including energy harvesting, energy storage, and thermoelectric cooling (Figure 1). These modules form a portable design intended for use in off-grid or resource-limited environments.
The energy-harvesting module is a multilayer PSC (Figure 1, left). The active layer is a perovskite absorber (ABX₃) sandwiched between a hole transport layer (HTL) and an electron transport layer (ETL). When sunlight strikes the perovskite, it generates electron-hole pairs. The ETL carries electrons toward the cathode, and the HTL carries holes toward the anode, producing a direct current (DC) at the electrodes. Compared with silicon photovoltaics, PSCs are attractive for low-cost and portable applications because they can be solution-processed, are lightweight, and have a tunable band gap.
As shown in the left schematic of Figure 1, the power generation unit utilizes a multilayer PSC structure. The device is composed of a perovskite absorber layer (ABX3) between a Hole Transport Layer (HTL) and an Electron Transport Layer (ETL). When incident solar energy strikes the perovskite layer, photoexcitation occurs, generating electron–hole pairs. The ETL selectively facilitates the transport of electrons toward the cathode, while the HTL directs holes toward the anode. This directed movement of charge carriers minimizes recombination losses and creates a direct current (DC), which is extracted through the electrodes to power the system. Compared with conventional silicon photovoltaics, PSCs offer high efficiency, low-cost fabrication, lightweight flexibility, and tunable band gaps, making them particularly suitable for portable medical applications.
The PSC is mounted on the exterior of a portable, high-insulation styrofoam container so that it is exposed to sunlight during transport or field use. The harvested DC is regulated by an internal charge-controller circuit and stored in a lithium-ion battery pack inside the container. The battery is important because solar input is intermittent. The cooler needs a buffered energy source to keep running when irradiance drops or at night. The thermal insulation of container reduces external heat ingress, which lowers the cooling load that the Peltier has to meet. The interior of the chamber is the storage space for vaccines or other temperature-sensitive medicines.
The cooling module is a Peltier thermoelectric device. When DC from the battery passes through it, a temperature gradient develops across its two faces. Heat is absorbed from the interior of the container (cold side) and rejected to the outside through a heatsink (hot side). The cooling rate can be adjusted by controlling the current. Unlike compressor-based refrigerators, Peltier coolers have no moving parts, which makes them quiet and low-maintenance, useful properties for portable medical hardware [10].
he PSC, lithium-ion battery, and Peltier cooler form an integrated architecture intended to operate without an external power source. Whether this design can hold the WHO vaccine cold-chain range of 2-8 °C, and what component-level scaling would be needed to do so reliably, is what we test in the rest of this study.
We fabricated the PSC in three stages. First, the transparent anode and hole transport layer (HTL) were deposited. Second, the perovskite absorber and a surface passivation layer were formed. Third, the electron transport layer (ETL) and top cathode were deposited. The first two stages used spin-coating from solution; the third used vacuum thermal evaporation.For the first stage, we used ITO-coated glass as the transparent anode. We then spin-coated nickel oxide (NiOₓ) followed by [4-(3,6-dimethyl-9H-carbazol-9-yl)butyl]phosphonic acid (Me-4PACz) to form the HTL. Spin-coating produces thin and uniform layers whose thickness can be controlled by the spin speed and solution concentration. After deposition, we annealed the films at 100 °C for 10 min to drive off residual solvent and improve adhesion to the substrate, both of which support hole extraction at the HTL/perovskite interface [11].For the second stage, we deposited the perovskite active layer using a two-step spin-coating program. A low-speed step to spread the precursor evenly across the substrate, followed by a high-speed step to set the final film thickness. This two-step approach helps control nucleation and grain growth during crystallization. We annealed the resulting film at 100 °C for 10 min to crystallize the perovskite phase. We then spin-coated a PDAI₂ passivation layer on top of the perovskite and annealed it under the same conditions. The passivation layer reduces surface defects, which lowers non-radiative recombination at the perovskite/ETL interface and improves device stability [8].For the third stage, we deposited the remaining layers by vacuum thermal evaporation, which allows precise thickness control through quartz-crystal monitoring and avoids solvent damage to the underlying perovskite. We evaporated C60 as the ETL, then a thin bathocuproine (BCP) buffer layer to improve energy-level alignment between C60 and the cathode, and finally a silver (Ag) cathode to complete the device [12]. The combination of solution processing for the bottom layers and vacuum evaporation for the top layers is a standard architecture for inverted (p-i-n) perovskite solar cells
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